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1 | \input texinfo |
2 | @setfilename stabs.info | |
3 | ||
4 | @c @finalout | |
5 | ||
6 | @ifinfo | |
7 | @format | |
8 | START-INFO-DIR-ENTRY | |
9 | * Stabs: (stabs). The "stabs" debugging information format. | |
10 | END-INFO-DIR-ENTRY | |
11 | @end format | |
12 | @end ifinfo | |
13 | ||
14 | @ifinfo | |
15 | This document describes the stabs debugging symbol tables. | |
16 | ||
17 | Copyright 1992, 93, 94, 95, 97, 1998 Free Software Foundation, Inc. | |
18 | Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon, | |
19 | and David MacKenzie. | |
20 | ||
21 | Permission is granted to make and distribute verbatim copies of | |
22 | this manual provided the copyright notice and this permission notice | |
23 | are preserved on all copies. | |
24 | ||
25 | @ignore | |
26 | Permission is granted to process this file through Tex and print the | |
27 | results, provided the printed document carries copying permission | |
28 | notice identical to this one except for the removal of this paragraph | |
29 | (this paragraph not being relevant to the printed manual). | |
30 | ||
31 | @end ignore | |
32 | Permission is granted to copy or distribute modified versions of this | |
33 | manual under the terms of the GPL (for which purpose this text may be | |
34 | regarded as a program in the language TeX). | |
35 | @end ifinfo | |
36 | ||
37 | @setchapternewpage odd | |
38 | @settitle STABS | |
39 | @titlepage | |
40 | @title The ``stabs'' debug format | |
41 | @author Julia Menapace, Jim Kingdon, David MacKenzie | |
42 | @author Cygnus Support | |
43 | @page | |
44 | @tex | |
45 | \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$ | |
46 | \xdef\manvers{\$Revision$} % For use in headers, footers too | |
47 | {\parskip=0pt | |
48 | \hfill Cygnus Support\par | |
49 | \hfill \manvers\par | |
50 | \hfill \TeX{}info \texinfoversion\par | |
51 | } | |
52 | @end tex | |
53 | ||
54 | @vskip 0pt plus 1filll | |
55 | Copyright @copyright{} 1992, 93, 94, 95, 97, 1998 Free Software Foundation, Inc. | |
56 | Contributed by Cygnus Support. | |
57 | ||
58 | Permission is granted to make and distribute verbatim copies of | |
59 | this manual provided the copyright notice and this permission notice | |
60 | are preserved on all copies. | |
61 | ||
62 | @end titlepage | |
63 | ||
64 | @ifinfo | |
65 | @node Top | |
66 | @top The "stabs" representation of debugging information | |
67 | ||
68 | This document describes the stabs debugging format. | |
69 | ||
70 | @menu | |
71 | * Overview:: Overview of stabs | |
72 | * Program Structure:: Encoding of the structure of the program | |
73 | * Constants:: Constants | |
74 | * Variables:: | |
75 | * Types:: Type definitions | |
76 | * Symbol Tables:: Symbol information in symbol tables | |
77 | * Cplusplus:: Stabs specific to C++ | |
78 | * Stab Types:: Symbol types in a.out files | |
79 | * Symbol Descriptors:: Table of symbol descriptors | |
80 | * Type Descriptors:: Table of type descriptors | |
81 | * Expanded Reference:: Reference information by stab type | |
bd79f757 | 82 | * Questions:: Questions and anomalies |
c906108c SS |
83 | * Stab Sections:: In some object file formats, stabs are |
84 | in sections. | |
85 | * Symbol Types Index:: Index of symbolic stab symbol type names. | |
86 | @end menu | |
87 | @end ifinfo | |
88 | ||
449f3b6c AC |
89 | @c TeX can handle the contents at the start but makeinfo 3.12 can not |
90 | @iftex | |
91 | @contents | |
92 | @end iftex | |
c906108c SS |
93 | |
94 | @node Overview | |
95 | @chapter Overview of Stabs | |
96 | ||
97 | @dfn{Stabs} refers to a format for information that describes a program | |
98 | to a debugger. This format was apparently invented by | |
99 | Peter Kessler at | |
100 | the University of California at Berkeley, for the @code{pdx} Pascal | |
101 | debugger; the format has spread widely since then. | |
102 | ||
103 | This document is one of the few published sources of documentation on | |
104 | stabs. It is believed to be comprehensive for stabs used by C. The | |
105 | lists of symbol descriptors (@pxref{Symbol Descriptors}) and type | |
106 | descriptors (@pxref{Type Descriptors}) are believed to be completely | |
107 | comprehensive. Stabs for COBOL-specific features and for variant | |
108 | records (used by Pascal and Modula-2) are poorly documented here. | |
109 | ||
110 | @c FIXME: Need to document all OS9000 stuff in GDB; see all references | |
111 | @c to os9k_stabs in stabsread.c. | |
112 | ||
113 | Other sources of information on stabs are @cite{Dbx and Dbxtool | |
114 | Interfaces}, 2nd edition, by Sun, 1988, and @cite{AIX Version 3.2 Files | |
115 | Reference}, Fourth Edition, September 1992, "dbx Stabstring Grammar" in | |
116 | the a.out section, page 2-31. This document is believed to incorporate | |
117 | the information from those two sources except where it explicitly directs | |
118 | you to them for more information. | |
119 | ||
120 | @menu | |
121 | * Flow:: Overview of debugging information flow | |
122 | * Stabs Format:: Overview of stab format | |
123 | * String Field:: The string field | |
124 | * C Example:: A simple example in C source | |
125 | * Assembly Code:: The simple example at the assembly level | |
126 | @end menu | |
127 | ||
128 | @node Flow | |
129 | @section Overview of Debugging Information Flow | |
130 | ||
131 | The GNU C compiler compiles C source in a @file{.c} file into assembly | |
132 | language in a @file{.s} file, which the assembler translates into | |
133 | a @file{.o} file, which the linker combines with other @file{.o} files and | |
134 | libraries to produce an executable file. | |
135 | ||
136 | With the @samp{-g} option, GCC puts in the @file{.s} file additional | |
137 | debugging information, which is slightly transformed by the assembler | |
138 | and linker, and carried through into the final executable. This | |
139 | debugging information describes features of the source file like line | |
140 | numbers, the types and scopes of variables, and function names, | |
141 | parameters, and scopes. | |
142 | ||
143 | For some object file formats, the debugging information is encapsulated | |
144 | in assembler directives known collectively as @dfn{stab} (symbol table) | |
145 | directives, which are interspersed with the generated code. Stabs are | |
146 | the native format for debugging information in the a.out and XCOFF | |
147 | object file formats. The GNU tools can also emit stabs in the COFF and | |
148 | ECOFF object file formats. | |
149 | ||
150 | The assembler adds the information from stabs to the symbol information | |
151 | it places by default in the symbol table and the string table of the | |
152 | @file{.o} file it is building. The linker consolidates the @file{.o} | |
153 | files into one executable file, with one symbol table and one string | |
154 | table. Debuggers use the symbol and string tables in the executable as | |
155 | a source of debugging information about the program. | |
156 | ||
157 | @node Stabs Format | |
158 | @section Overview of Stab Format | |
159 | ||
160 | There are three overall formats for stab assembler directives, | |
161 | differentiated by the first word of the stab. The name of the directive | |
162 | describes which combination of four possible data fields follows. It is | |
163 | either @code{.stabs} (string), @code{.stabn} (number), or @code{.stabd} | |
164 | (dot). IBM's XCOFF assembler uses @code{.stabx} (and some other | |
165 | directives such as @code{.file} and @code{.bi}) instead of | |
166 | @code{.stabs}, @code{.stabn} or @code{.stabd}. | |
167 | ||
168 | The overall format of each class of stab is: | |
169 | ||
170 | @example | |
171 | .stabs "@var{string}",@var{type},@var{other},@var{desc},@var{value} | |
172 | .stabn @var{type},@var{other},@var{desc},@var{value} | |
173 | .stabd @var{type},@var{other},@var{desc} | |
174 | .stabx "@var{string}",@var{value},@var{type},@var{sdb-type} | |
175 | @end example | |
176 | ||
177 | @c what is the correct term for "current file location"? My AIX | |
178 | @c assembler manual calls it "the value of the current location counter". | |
179 | For @code{.stabn} and @code{.stabd}, there is no @var{string} (the | |
180 | @code{n_strx} field is zero; see @ref{Symbol Tables}). For | |
181 | @code{.stabd}, the @var{value} field is implicit and has the value of | |
182 | the current file location. For @code{.stabx}, the @var{sdb-type} field | |
183 | is unused for stabs and can always be set to zero. The @var{other} | |
184 | field is almost always unused and can be set to zero. | |
185 | ||
186 | The number in the @var{type} field gives some basic information about | |
187 | which type of stab this is (or whether it @emph{is} a stab, as opposed | |
188 | to an ordinary symbol). Each valid type number defines a different stab | |
189 | type; further, the stab type defines the exact interpretation of, and | |
190 | possible values for, any remaining @var{string}, @var{desc}, or | |
191 | @var{value} fields present in the stab. @xref{Stab Types}, for a list | |
192 | in numeric order of the valid @var{type} field values for stab directives. | |
193 | ||
194 | @node String Field | |
195 | @section The String Field | |
196 | ||
197 | For most stabs the string field holds the meat of the | |
198 | debugging information. The flexible nature of this field | |
199 | is what makes stabs extensible. For some stab types the string field | |
200 | contains only a name. For other stab types the contents can be a great | |
201 | deal more complex. | |
202 | ||
203 | The overall format of the string field for most stab types is: | |
204 | ||
205 | @example | |
206 | "@var{name}:@var{symbol-descriptor} @var{type-information}" | |
207 | @end example | |
208 | ||
209 | @var{name} is the name of the symbol represented by the stab; it can | |
210 | contain a pair of colons (@pxref{Nested Symbols}). @var{name} can be | |
211 | omitted, which means the stab represents an unnamed object. For | |
212 | example, @samp{:t10=*2} defines type 10 as a pointer to type 2, but does | |
213 | not give the type a name. Omitting the @var{name} field is supported by | |
214 | AIX dbx and GDB after about version 4.8, but not other debuggers. GCC | |
215 | sometimes uses a single space as the name instead of omitting the name | |
216 | altogether; apparently that is supported by most debuggers. | |
217 | ||
218 | The @var{symbol-descriptor} following the @samp{:} is an alphabetic | |
219 | character that tells more specifically what kind of symbol the stab | |
220 | represents. If the @var{symbol-descriptor} is omitted, but type | |
221 | information follows, then the stab represents a local variable. For a | |
222 | list of symbol descriptors, see @ref{Symbol Descriptors}. The @samp{c} | |
223 | symbol descriptor is an exception in that it is not followed by type | |
224 | information. @xref{Constants}. | |
225 | ||
226 | @var{type-information} is either a @var{type-number}, or | |
227 | @samp{@var{type-number}=}. A @var{type-number} alone is a type | |
228 | reference, referring directly to a type that has already been defined. | |
229 | ||
230 | The @samp{@var{type-number}=} form is a type definition, where the | |
231 | number represents a new type which is about to be defined. The type | |
232 | definition may refer to other types by number, and those type numbers | |
233 | may be followed by @samp{=} and nested definitions. Also, the Lucid | |
234 | compiler will repeat @samp{@var{type-number}=} more than once if it | |
235 | wants to define several type numbers at once. | |
236 | ||
237 | In a type definition, if the character that follows the equals sign is | |
238 | non-numeric then it is a @var{type-descriptor}, and tells what kind of | |
239 | type is about to be defined. Any other values following the | |
240 | @var{type-descriptor} vary, depending on the @var{type-descriptor}. | |
241 | @xref{Type Descriptors}, for a list of @var{type-descriptor} values. If | |
242 | a number follows the @samp{=} then the number is a @var{type-reference}. | |
243 | For a full description of types, @ref{Types}. | |
244 | ||
245 | A @var{type-number} is often a single number. The GNU and Sun tools | |
246 | additionally permit a @var{type-number} to be a pair | |
247 | (@var{file-number},@var{filetype-number}) (the parentheses appear in the | |
248 | string, and serve to distinguish the two cases). The @var{file-number} | |
bd79f757 ND |
249 | is 0 for the base source file, 1 for the first included file, 2 for the |
250 | next, and so on. The @var{filetype-number} is a number starting with | |
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251 | 1 which is incremented for each new type defined in the file. |
252 | (Separating the file number and the type number permits the | |
253 | @code{N_BINCL} optimization to succeed more often; see @ref{Include | |
254 | Files}). | |
255 | ||
256 | There is an AIX extension for type attributes. Following the @samp{=} | |
257 | are any number of type attributes. Each one starts with @samp{@@} and | |
258 | ends with @samp{;}. Debuggers, including AIX's dbx and GDB 4.10, skip | |
259 | any type attributes they do not recognize. GDB 4.9 and other versions | |
260 | of dbx may not do this. Because of a conflict with C++ | |
261 | (@pxref{Cplusplus}), new attributes should not be defined which begin | |
262 | with a digit, @samp{(}, or @samp{-}; GDB may be unable to distinguish | |
263 | those from the C++ type descriptor @samp{@@}. The attributes are: | |
264 | ||
265 | @table @code | |
266 | @item a@var{boundary} | |
267 | @var{boundary} is an integer specifying the alignment. I assume it | |
268 | applies to all variables of this type. | |
269 | ||
270 | @item p@var{integer} | |
271 | Pointer class (for checking). Not sure what this means, or how | |
272 | @var{integer} is interpreted. | |
273 | ||
274 | @item P | |
275 | Indicate this is a packed type, meaning that structure fields or array | |
276 | elements are placed more closely in memory, to save memory at the | |
277 | expense of speed. | |
278 | ||
279 | @item s@var{size} | |
280 | Size in bits of a variable of this type. This is fully supported by GDB | |
281 | 4.11 and later. | |
282 | ||
283 | @item S | |
284 | Indicate that this type is a string instead of an array of characters, | |
285 | or a bitstring instead of a set. It doesn't change the layout of the | |
286 | data being represented, but does enable the debugger to know which type | |
287 | it is. | |
288 | @end table | |
289 | ||
290 | All of this can make the string field quite long. All versions of GDB, | |
291 | and some versions of dbx, can handle arbitrarily long strings. But many | |
292 | versions of dbx (or assemblers or linkers, I'm not sure which) | |
293 | cretinously limit the strings to about 80 characters, so compilers which | |
294 | must work with such systems need to split the @code{.stabs} directive | |
295 | into several @code{.stabs} directives. Each stab duplicates every field | |
296 | except the string field. The string field of every stab except the last | |
297 | is marked as continued with a backslash at the end (in the assembly code | |
298 | this may be written as a double backslash, depending on the assembler). | |
299 | Removing the backslashes and concatenating the string fields of each | |
300 | stab produces the original, long string. Just to be incompatible (or so | |
301 | they don't have to worry about what the assembler does with | |
302 | backslashes), AIX can use @samp{?} instead of backslash. | |
303 | ||
304 | @node C Example | |
305 | @section A Simple Example in C Source | |
306 | ||
307 | To get the flavor of how stabs describe source information for a C | |
308 | program, let's look at the simple program: | |
309 | ||
310 | @example | |
311 | main() | |
312 | @{ | |
313 | printf("Hello world"); | |
314 | @} | |
315 | @end example | |
316 | ||
317 | When compiled with @samp{-g}, the program above yields the following | |
318 | @file{.s} file. Line numbers have been added to make it easier to refer | |
319 | to parts of the @file{.s} file in the description of the stabs that | |
320 | follows. | |
321 | ||
322 | @node Assembly Code | |
323 | @section The Simple Example at the Assembly Level | |
324 | ||
325 | This simple ``hello world'' example demonstrates several of the stab | |
326 | types used to describe C language source files. | |
327 | ||
328 | @example | |
329 | 1 gcc2_compiled.: | |
330 | 2 .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0 | |
331 | 3 .stabs "hello.c",100,0,0,Ltext0 | |
332 | 4 .text | |
333 | 5 Ltext0: | |
334 | 6 .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0 | |
335 | 7 .stabs "char:t2=r2;0;127;",128,0,0,0 | |
336 | 8 .stabs "long int:t3=r1;-2147483648;2147483647;",128,0,0,0 | |
337 | 9 .stabs "unsigned int:t4=r1;0;-1;",128,0,0,0 | |
338 | 10 .stabs "long unsigned int:t5=r1;0;-1;",128,0,0,0 | |
339 | 11 .stabs "short int:t6=r1;-32768;32767;",128,0,0,0 | |
340 | 12 .stabs "long long int:t7=r1;0;-1;",128,0,0,0 | |
341 | 13 .stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0 | |
342 | 14 .stabs "long long unsigned int:t9=r1;0;-1;",128,0,0,0 | |
343 | 15 .stabs "signed char:t10=r1;-128;127;",128,0,0,0 | |
344 | 16 .stabs "unsigned char:t11=r1;0;255;",128,0,0,0 | |
345 | 17 .stabs "float:t12=r1;4;0;",128,0,0,0 | |
346 | 18 .stabs "double:t13=r1;8;0;",128,0,0,0 | |
347 | 19 .stabs "long double:t14=r1;8;0;",128,0,0,0 | |
348 | 20 .stabs "void:t15=15",128,0,0,0 | |
349 | 21 .align 4 | |
350 | 22 LC0: | |
351 | 23 .ascii "Hello, world!\12\0" | |
352 | 24 .align 4 | |
353 | 25 .global _main | |
354 | 26 .proc 1 | |
355 | 27 _main: | |
356 | 28 .stabn 68,0,4,LM1 | |
357 | 29 LM1: | |
358 | 30 !#PROLOGUE# 0 | |
359 | 31 save %sp,-136,%sp | |
360 | 32 !#PROLOGUE# 1 | |
361 | 33 call ___main,0 | |
362 | 34 nop | |
363 | 35 .stabn 68,0,5,LM2 | |
364 | 36 LM2: | |
365 | 37 LBB2: | |
366 | 38 sethi %hi(LC0),%o1 | |
367 | 39 or %o1,%lo(LC0),%o0 | |
368 | 40 call _printf,0 | |
369 | 41 nop | |
370 | 42 .stabn 68,0,6,LM3 | |
371 | 43 LM3: | |
372 | 44 LBE2: | |
373 | 45 .stabn 68,0,6,LM4 | |
374 | 46 LM4: | |
375 | 47 L1: | |
376 | 48 ret | |
377 | 49 restore | |
378 | 50 .stabs "main:F1",36,0,0,_main | |
379 | 51 .stabn 192,0,0,LBB2 | |
380 | 52 .stabn 224,0,0,LBE2 | |
381 | @end example | |
382 | ||
383 | @node Program Structure | |
384 | @chapter Encoding the Structure of the Program | |
385 | ||
386 | The elements of the program structure that stabs encode include the name | |
387 | of the main function, the names of the source and include files, the | |
388 | line numbers, procedure names and types, and the beginnings and ends of | |
389 | blocks of code. | |
390 | ||
391 | @menu | |
392 | * Main Program:: Indicate what the main program is | |
393 | * Source Files:: The path and name of the source file | |
394 | * Include Files:: Names of include files | |
395 | * Line Numbers:: | |
396 | * Procedures:: | |
397 | * Nested Procedures:: | |
398 | * Block Structure:: | |
399 | * Alternate Entry Points:: Entering procedures except at the beginning. | |
400 | @end menu | |
401 | ||
402 | @node Main Program | |
403 | @section Main Program | |
404 | ||
405 | @findex N_MAIN | |
406 | Most languages allow the main program to have any name. The | |
407 | @code{N_MAIN} stab type tells the debugger the name that is used in this | |
408 | program. Only the string field is significant; it is the name of | |
409 | a function which is the main program. Most C compilers do not use this | |
410 | stab (they expect the debugger to assume that the name is @code{main}), | |
411 | but some C compilers emit an @code{N_MAIN} stab for the @code{main} | |
412 | function. I'm not sure how XCOFF handles this. | |
413 | ||
414 | @node Source Files | |
415 | @section Paths and Names of the Source Files | |
416 | ||
417 | @findex N_SO | |
418 | Before any other stabs occur, there must be a stab specifying the source | |
419 | file. This information is contained in a symbol of stab type | |
420 | @code{N_SO}; the string field contains the name of the file. The | |
421 | value of the symbol is the start address of the portion of the | |
422 | text section corresponding to that file. | |
423 | ||
424 | With the Sun Solaris2 compiler, the desc field contains a | |
425 | source-language code. | |
426 | @c Do the debuggers use it? What are the codes? -djm | |
427 | ||
428 | Some compilers (for example, GCC2 and SunOS4 @file{/bin/cc}) also | |
429 | include the directory in which the source was compiled, in a second | |
430 | @code{N_SO} symbol preceding the one containing the file name. This | |
431 | symbol can be distinguished by the fact that it ends in a slash. Code | |
432 | from the @code{cfront} C++ compiler can have additional @code{N_SO} symbols for | |
433 | nonexistent source files after the @code{N_SO} for the real source file; | |
434 | these are believed to contain no useful information. | |
435 | ||
436 | For example: | |
437 | ||
438 | @example | |
439 | .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0 # @r{100 is N_SO} | |
440 | .stabs "hello.c",100,0,0,Ltext0 | |
441 | .text | |
442 | Ltext0: | |
443 | @end example | |
444 | ||
445 | @findex C_FILE | |
446 | Instead of @code{N_SO} symbols, XCOFF uses a @code{.file} assembler | |
447 | directive which assembles to a @code{C_FILE} symbol; explaining this in | |
448 | detail is outside the scope of this document. | |
449 | ||
450 | @c FIXME: Exactly when should the empty N_SO be used? Why? | |
451 | If it is useful to indicate the end of a source file, this is done with | |
452 | an @code{N_SO} symbol with an empty string for the name. The value is | |
453 | the address of the end of the text section for the file. For some | |
454 | systems, there is no indication of the end of a source file, and you | |
455 | just need to figure it ended when you see an @code{N_SO} for a different | |
456 | source file, or a symbol ending in @code{.o} (which at least some | |
457 | linkers insert to mark the start of a new @code{.o} file). | |
458 | ||
459 | @node Include Files | |
460 | @section Names of Include Files | |
461 | ||
462 | There are several schemes for dealing with include files: the | |
463 | traditional @code{N_SOL} approach, Sun's @code{N_BINCL} approach, and the | |
464 | XCOFF @code{C_BINCL} approach (which despite the similar name has little in | |
465 | common with @code{N_BINCL}). | |
466 | ||
467 | @findex N_SOL | |
468 | An @code{N_SOL} symbol specifies which include file subsequent symbols | |
469 | refer to. The string field is the name of the file and the value is the | |
470 | text address corresponding to the end of the previous include file and | |
471 | the start of this one. To specify the main source file again, use an | |
472 | @code{N_SOL} symbol with the name of the main source file. | |
473 | ||
474 | @findex N_BINCL | |
475 | @findex N_EINCL | |
476 | @findex N_EXCL | |
477 | The @code{N_BINCL} approach works as follows. An @code{N_BINCL} symbol | |
478 | specifies the start of an include file. In an object file, only the | |
479 | string is significant; the linker puts data into some of the other | |
480 | fields. The end of the include file is marked by an @code{N_EINCL} | |
481 | symbol (which has no string field). In an object file, there is no | |
482 | significant data in the @code{N_EINCL} symbol. @code{N_BINCL} and | |
483 | @code{N_EINCL} can be nested. | |
484 | ||
485 | If the linker detects that two source files have identical stabs between | |
486 | an @code{N_BINCL} and @code{N_EINCL} pair (as will generally be the case | |
487 | for a header file), then it only puts out the stabs once. Each | |
bd79f757 | 488 | additional occurrence is replaced by an @code{N_EXCL} symbol. I believe |
c906108c SS |
489 | the GNU linker and the Sun (both SunOS4 and Solaris) linker are the only |
490 | ones which supports this feature. | |
491 | ||
492 | A linker which supports this feature will set the value of a | |
493 | @code{N_BINCL} symbol to the total of all the characters in the stabs | |
494 | strings included in the header file, omitting any file numbers. The | |
495 | value of an @code{N_EXCL} symbol is the same as the value of the | |
496 | @code{N_BINCL} symbol it replaces. This information can be used to | |
497 | match up @code{N_EXCL} and @code{N_BINCL} symbols which have the same | |
498 | filename. The @code{N_EINCL} value, and the values of the other and | |
499 | description fields for all three, appear to always be zero. | |
500 | ||
501 | @findex C_BINCL | |
502 | @findex C_EINCL | |
503 | For the start of an include file in XCOFF, use the @file{.bi} assembler | |
504 | directive, which generates a @code{C_BINCL} symbol. A @file{.ei} | |
505 | directive, which generates a @code{C_EINCL} symbol, denotes the end of | |
506 | the include file. Both directives are followed by the name of the | |
507 | source file in quotes, which becomes the string for the symbol. | |
508 | The value of each symbol, produced automatically by the assembler | |
509 | and linker, is the offset into the executable of the beginning | |
510 | (inclusive, as you'd expect) or end (inclusive, as you would not expect) | |
511 | of the portion of the COFF line table that corresponds to this include | |
512 | file. @code{C_BINCL} and @code{C_EINCL} do not nest. | |
513 | ||
514 | @node Line Numbers | |
515 | @section Line Numbers | |
516 | ||
517 | @findex N_SLINE | |
518 | An @code{N_SLINE} symbol represents the start of a source line. The | |
519 | desc field contains the line number and the value contains the code | |
520 | address for the start of that source line. On most machines the address | |
521 | is absolute; for stabs in sections (@pxref{Stab Sections}), it is | |
522 | relative to the function in which the @code{N_SLINE} symbol occurs. | |
523 | ||
524 | @findex N_DSLINE | |
525 | @findex N_BSLINE | |
526 | GNU documents @code{N_DSLINE} and @code{N_BSLINE} symbols for line | |
527 | numbers in the data or bss segments, respectively. They are identical | |
528 | to @code{N_SLINE} but are relocated differently by the linker. They | |
529 | were intended to be used to describe the source location of a variable | |
530 | declaration, but I believe that GCC2 actually puts the line number in | |
531 | the desc field of the stab for the variable itself. GDB has been | |
532 | ignoring these symbols (unless they contain a string field) since | |
533 | at least GDB 3.5. | |
534 | ||
535 | For single source lines that generate discontiguous code, such as flow | |
536 | of control statements, there may be more than one line number entry for | |
537 | the same source line. In this case there is a line number entry at the | |
538 | start of each code range, each with the same line number. | |
539 | ||
540 | XCOFF does not use stabs for line numbers. Instead, it uses COFF line | |
541 | numbers (which are outside the scope of this document). Standard COFF | |
542 | line numbers cannot deal with include files, but in XCOFF this is fixed | |
543 | with the @code{C_BINCL} method of marking include files (@pxref{Include | |
544 | Files}). | |
545 | ||
546 | @node Procedures | |
547 | @section Procedures | |
548 | ||
549 | @findex N_FUN, for functions | |
550 | @findex N_FNAME | |
551 | @findex N_STSYM, for functions (Sun acc) | |
552 | @findex N_GSYM, for functions (Sun acc) | |
553 | All of the following stabs normally use the @code{N_FUN} symbol type. | |
554 | However, Sun's @code{acc} compiler on SunOS4 uses @code{N_GSYM} and | |
555 | @code{N_STSYM}, which means that the value of the stab for the function | |
556 | is useless and the debugger must get the address of the function from | |
557 | the non-stab symbols instead. On systems where non-stab symbols have | |
558 | leading underscores, the stabs will lack underscores and the debugger | |
559 | needs to know about the leading underscore to match up the stab and the | |
560 | non-stab symbol. BSD Fortran is said to use @code{N_FNAME} with the | |
561 | same restriction; the value of the symbol is not useful (I'm not sure it | |
562 | really does use this, because GDB doesn't handle this and no one has | |
563 | complained). | |
564 | ||
565 | @findex C_FUN | |
566 | A function is represented by an @samp{F} symbol descriptor for a global | |
567 | (extern) function, and @samp{f} for a static (local) function. For | |
568 | a.out, the value of the symbol is the address of the start of the | |
569 | function; it is already relocated. For stabs in ELF, the SunPRO | |
570 | compiler version 2.0.1 and GCC put out an address which gets relocated | |
571 | by the linker. In a future release SunPRO is planning to put out zero, | |
572 | in which case the address can be found from the ELF (non-stab) symbol. | |
573 | Because looking things up in the ELF symbols would probably be slow, I'm | |
574 | not sure how to find which symbol of that name is the right one, and | |
575 | this doesn't provide any way to deal with nested functions, it would | |
576 | probably be better to make the value of the stab an address relative to | |
577 | the start of the file, or just absolute. See @ref{ELF Linker | |
578 | Relocation} for more information on linker relocation of stabs in ELF | |
579 | files. For XCOFF, the stab uses the @code{C_FUN} storage class and the | |
580 | value of the stab is meaningless; the address of the function can be | |
581 | found from the csect symbol (XTY_LD/XMC_PR). | |
582 | ||
583 | The type information of the stab represents the return type of the | |
584 | function; thus @samp{foo:f5} means that foo is a function returning type | |
585 | 5. There is no need to try to get the line number of the start of the | |
586 | function from the stab for the function; it is in the next | |
587 | @code{N_SLINE} symbol. | |
588 | ||
589 | @c FIXME: verify whether the "I suspect" below is true or not. | |
590 | Some compilers (such as Sun's Solaris compiler) support an extension for | |
591 | specifying the types of the arguments. I suspect this extension is not | |
592 | used for old (non-prototyped) function definitions in C. If the | |
593 | extension is in use, the type information of the stab for the function | |
594 | is followed by type information for each argument, with each argument | |
595 | preceded by @samp{;}. An argument type of 0 means that additional | |
596 | arguments are being passed, whose types and number may vary (@samp{...} | |
597 | in ANSI C). GDB has tolerated this extension (parsed the syntax, if not | |
598 | necessarily used the information) since at least version 4.8; I don't | |
599 | know whether all versions of dbx tolerate it. The argument types given | |
600 | here are not redundant with the symbols for the formal parameters | |
601 | (@pxref{Parameters}); they are the types of the arguments as they are | |
602 | passed, before any conversions might take place. For example, if a C | |
603 | function which is declared without a prototype takes a @code{float} | |
604 | argument, the value is passed as a @code{double} but then converted to a | |
605 | @code{float}. Debuggers need to use the types given in the arguments | |
606 | when printing values, but when calling the function they need to use the | |
607 | types given in the symbol defining the function. | |
608 | ||
609 | If the return type and types of arguments of a function which is defined | |
610 | in another source file are specified (i.e., a function prototype in ANSI | |
611 | C), traditionally compilers emit no stab; the only way for the debugger | |
612 | to find the information is if the source file where the function is | |
613 | defined was also compiled with debugging symbols. As an extension the | |
614 | Solaris compiler uses symbol descriptor @samp{P} followed by the return | |
615 | type of the function, followed by the arguments, each preceded by | |
616 | @samp{;}, as in a stab with symbol descriptor @samp{f} or @samp{F}. | |
617 | This use of symbol descriptor @samp{P} can be distinguished from its use | |
618 | for register parameters (@pxref{Register Parameters}) by the fact that it has | |
619 | symbol type @code{N_FUN}. | |
620 | ||
621 | The AIX documentation also defines symbol descriptor @samp{J} as an | |
622 | internal function. I assume this means a function nested within another | |
623 | function. It also says symbol descriptor @samp{m} is a module in | |
624 | Modula-2 or extended Pascal. | |
625 | ||
626 | Procedures (functions which do not return values) are represented as | |
627 | functions returning the @code{void} type in C. I don't see why this couldn't | |
628 | be used for all languages (inventing a @code{void} type for this purpose if | |
629 | necessary), but the AIX documentation defines @samp{I}, @samp{P}, and | |
630 | @samp{Q} for internal, global, and static procedures, respectively. | |
631 | These symbol descriptors are unusual in that they are not followed by | |
632 | type information. | |
633 | ||
634 | The following example shows a stab for a function @code{main} which | |
635 | returns type number @code{1}. The @code{_main} specified for the value | |
636 | is a reference to an assembler label which is used to fill in the start | |
637 | address of the function. | |
638 | ||
639 | @example | |
640 | .stabs "main:F1",36,0,0,_main # @r{36 is N_FUN} | |
641 | @end example | |
642 | ||
643 | The stab representing a procedure is located immediately following the | |
644 | code of the procedure. This stab is in turn directly followed by a | |
645 | group of other stabs describing elements of the procedure. These other | |
646 | stabs describe the procedure's parameters, its block local variables, and | |
647 | its block structure. | |
648 | ||
649 | If functions can appear in different sections, then the debugger may not | |
650 | be able to find the end of a function. Recent versions of GCC will mark | |
651 | the end of a function with an @code{N_FUN} symbol with an empty string | |
652 | for the name. The value is the address of the end of the current | |
653 | function. Without such a symbol, there is no indication of the address | |
654 | of the end of a function, and you must assume that it ended at the | |
655 | starting address of the next function or at the end of the text section | |
656 | for the program. | |
657 | ||
658 | @node Nested Procedures | |
659 | @section Nested Procedures | |
660 | ||
661 | For any of the symbol descriptors representing procedures, after the | |
662 | symbol descriptor and the type information is optionally a scope | |
663 | specifier. This consists of a comma, the name of the procedure, another | |
664 | comma, and the name of the enclosing procedure. The first name is local | |
665 | to the scope specified, and seems to be redundant with the name of the | |
666 | symbol (before the @samp{:}). This feature is used by GCC, and | |
667 | presumably Pascal, Modula-2, etc., compilers, for nested functions. | |
668 | ||
669 | If procedures are nested more than one level deep, only the immediately | |
670 | containing scope is specified. For example, this code: | |
671 | ||
672 | @example | |
673 | int | |
674 | foo (int x) | |
675 | @{ | |
676 | int bar (int y) | |
677 | @{ | |
678 | int baz (int z) | |
679 | @{ | |
680 | return x + y + z; | |
681 | @} | |
682 | return baz (x + 2 * y); | |
683 | @} | |
684 | return x + bar (3 * x); | |
685 | @} | |
686 | @end example | |
687 | ||
688 | @noindent | |
689 | produces the stabs: | |
690 | ||
691 | @example | |
692 | .stabs "baz:f1,baz,bar",36,0,0,_baz.15 # @r{36 is N_FUN} | |
693 | .stabs "bar:f1,bar,foo",36,0,0,_bar.12 | |
694 | .stabs "foo:F1",36,0,0,_foo | |
695 | @end example | |
696 | ||
697 | @node Block Structure | |
698 | @section Block Structure | |
699 | ||
700 | @findex N_LBRAC | |
701 | @findex N_RBRAC | |
702 | @c For GCC 2.5.8 or so stabs-in-coff, these are absolute instead of | |
703 | @c function relative (as documented below). But GDB has never been able | |
704 | @c to deal with that (it had wanted them to be relative to the file, but | |
705 | @c I just fixed that (between GDB 4.12 and 4.13)), so it is function | |
706 | @c relative just like ELF and SOM and the below documentation. | |
707 | The program's block structure is represented by the @code{N_LBRAC} (left | |
708 | brace) and the @code{N_RBRAC} (right brace) stab types. The variables | |
709 | defined inside a block precede the @code{N_LBRAC} symbol for most | |
710 | compilers, including GCC. Other compilers, such as the Convex, Acorn | |
711 | RISC machine, and Sun @code{acc} compilers, put the variables after the | |
712 | @code{N_LBRAC} symbol. The values of the @code{N_LBRAC} and | |
713 | @code{N_RBRAC} symbols are the start and end addresses of the code of | |
714 | the block, respectively. For most machines, they are relative to the | |
715 | starting address of this source file. For the Gould NP1, they are | |
716 | absolute. For stabs in sections (@pxref{Stab Sections}), they are | |
717 | relative to the function in which they occur. | |
718 | ||
719 | The @code{N_LBRAC} and @code{N_RBRAC} stabs that describe the block | |
720 | scope of a procedure are located after the @code{N_FUN} stab that | |
721 | represents the procedure itself. | |
722 | ||
723 | Sun documents the desc field of @code{N_LBRAC} and | |
724 | @code{N_RBRAC} symbols as containing the nesting level of the block. | |
725 | However, dbx seems to not care, and GCC always sets desc to | |
726 | zero. | |
727 | ||
728 | @findex .bb | |
729 | @findex .be | |
730 | @findex C_BLOCK | |
731 | For XCOFF, block scope is indicated with @code{C_BLOCK} symbols. If the | |
732 | name of the symbol is @samp{.bb}, then it is the beginning of the block; | |
733 | if the name of the symbol is @samp{.be}; it is the end of the block. | |
734 | ||
735 | @node Alternate Entry Points | |
736 | @section Alternate Entry Points | |
737 | ||
738 | @findex N_ENTRY | |
739 | @findex C_ENTRY | |
740 | Some languages, like Fortran, have the ability to enter procedures at | |
741 | some place other than the beginning. One can declare an alternate entry | |
742 | point. The @code{N_ENTRY} stab is for this; however, the Sun FORTRAN | |
743 | compiler doesn't use it. According to AIX documentation, only the name | |
744 | of a @code{C_ENTRY} stab is significant; the address of the alternate | |
745 | entry point comes from the corresponding external symbol. A previous | |
746 | revision of this document said that the value of an @code{N_ENTRY} stab | |
747 | was the address of the alternate entry point, but I don't know the | |
748 | source for that information. | |
749 | ||
750 | @node Constants | |
751 | @chapter Constants | |
752 | ||
753 | The @samp{c} symbol descriptor indicates that this stab represents a | |
754 | constant. This symbol descriptor is an exception to the general rule | |
755 | that symbol descriptors are followed by type information. Instead, it | |
756 | is followed by @samp{=} and one of the following: | |
757 | ||
758 | @table @code | |
759 | @item b @var{value} | |
760 | Boolean constant. @var{value} is a numeric value; I assume it is 0 for | |
761 | false or 1 for true. | |
762 | ||
763 | @item c @var{value} | |
764 | Character constant. @var{value} is the numeric value of the constant. | |
765 | ||
766 | @item e @var{type-information} , @var{value} | |
767 | Constant whose value can be represented as integral. | |
768 | @var{type-information} is the type of the constant, as it would appear | |
769 | after a symbol descriptor (@pxref{String Field}). @var{value} is the | |
770 | numeric value of the constant. GDB 4.9 does not actually get the right | |
771 | value if @var{value} does not fit in a host @code{int}, but it does not | |
772 | do anything violent, and future debuggers could be extended to accept | |
773 | integers of any size (whether unsigned or not). This constant type is | |
774 | usually documented as being only for enumeration constants, but GDB has | |
775 | never imposed that restriction; I don't know about other debuggers. | |
776 | ||
777 | @item i @var{value} | |
778 | Integer constant. @var{value} is the numeric value. The type is some | |
779 | sort of generic integer type (for GDB, a host @code{int}); to specify | |
780 | the type explicitly, use @samp{e} instead. | |
781 | ||
782 | @item r @var{value} | |
783 | Real constant. @var{value} is the real value, which can be @samp{INF} | |
784 | (optionally preceded by a sign) for infinity, @samp{QNAN} for a quiet | |
785 | NaN (not-a-number), or @samp{SNAN} for a signalling NaN. If it is a | |
786 | normal number the format is that accepted by the C library function | |
787 | @code{atof}. | |
788 | ||
789 | @item s @var{string} | |
790 | String constant. @var{string} is a string enclosed in either @samp{'} | |
791 | (in which case @samp{'} characters within the string are represented as | |
792 | @samp{\'} or @samp{"} (in which case @samp{"} characters within the | |
793 | string are represented as @samp{\"}). | |
794 | ||
795 | @item S @var{type-information} , @var{elements} , @var{bits} , @var{pattern} | |
796 | Set constant. @var{type-information} is the type of the constant, as it | |
797 | would appear after a symbol descriptor (@pxref{String Field}). | |
798 | @var{elements} is the number of elements in the set (does this means | |
799 | how many bits of @var{pattern} are actually used, which would be | |
800 | redundant with the type, or perhaps the number of bits set in | |
801 | @var{pattern}? I don't get it), @var{bits} is the number of bits in the | |
802 | constant (meaning it specifies the length of @var{pattern}, I think), | |
803 | and @var{pattern} is a hexadecimal representation of the set. AIX | |
804 | documentation refers to a limit of 32 bytes, but I see no reason why | |
805 | this limit should exist. This form could probably be used for arbitrary | |
806 | constants, not just sets; the only catch is that @var{pattern} should be | |
807 | understood to be target, not host, byte order and format. | |
808 | @end table | |
809 | ||
810 | The boolean, character, string, and set constants are not supported by | |
811 | GDB 4.9, but it ignores them. GDB 4.8 and earlier gave an error | |
812 | message and refused to read symbols from the file containing the | |
813 | constants. | |
814 | ||
815 | The above information is followed by @samp{;}. | |
816 | ||
817 | @node Variables | |
818 | @chapter Variables | |
819 | ||
820 | Different types of stabs describe the various ways that variables can be | |
821 | allocated: on the stack, globally, in registers, in common blocks, | |
822 | statically, or as arguments to a function. | |
823 | ||
824 | @menu | |
825 | * Stack Variables:: Variables allocated on the stack. | |
826 | * Global Variables:: Variables used by more than one source file. | |
827 | * Register Variables:: Variables in registers. | |
828 | * Common Blocks:: Variables statically allocated together. | |
829 | * Statics:: Variables local to one source file. | |
830 | * Based Variables:: Fortran pointer based variables. | |
831 | * Parameters:: Variables for arguments to functions. | |
832 | @end menu | |
833 | ||
834 | @node Stack Variables | |
835 | @section Automatic Variables Allocated on the Stack | |
836 | ||
837 | If a variable's scope is local to a function and its lifetime is only as | |
838 | long as that function executes (C calls such variables | |
839 | @dfn{automatic}), it can be allocated in a register (@pxref{Register | |
840 | Variables}) or on the stack. | |
841 | ||
842 | @findex N_LSYM, for stack variables | |
843 | @findex C_LSYM | |
844 | Each variable allocated on the stack has a stab with the symbol | |
845 | descriptor omitted. Since type information should begin with a digit, | |
846 | @samp{-}, or @samp{(}, only those characters precluded from being used | |
847 | for symbol descriptors. However, the Acorn RISC machine (ARM) is said | |
848 | to get this wrong: it puts out a mere type definition here, without the | |
849 | preceding @samp{@var{type-number}=}. This is a bad idea; there is no | |
850 | guarantee that type descriptors are distinct from symbol descriptors. | |
851 | Stabs for stack variables use the @code{N_LSYM} stab type, or | |
852 | @code{C_LSYM} for XCOFF. | |
853 | ||
854 | The value of the stab is the offset of the variable within the | |
855 | local variables. On most machines this is an offset from the frame | |
856 | pointer and is negative. The location of the stab specifies which block | |
857 | it is defined in; see @ref{Block Structure}. | |
858 | ||
859 | For example, the following C code: | |
860 | ||
861 | @example | |
862 | int | |
863 | main () | |
864 | @{ | |
865 | int x; | |
866 | @} | |
867 | @end example | |
868 | ||
869 | produces the following stabs: | |
870 | ||
871 | @example | |
872 | .stabs "main:F1",36,0,0,_main # @r{36 is N_FUN} | |
873 | .stabs "x:1",128,0,0,-12 # @r{128 is N_LSYM} | |
874 | .stabn 192,0,0,LBB2 # @r{192 is N_LBRAC} | |
875 | .stabn 224,0,0,LBE2 # @r{224 is N_RBRAC} | |
876 | @end example | |
877 | ||
085dd6e6 | 878 | See @ref{Procedures} for more information on the @code{N_FUN} stab, and |
c906108c SS |
879 | @ref{Block Structure} for more information on the @code{N_LBRAC} and |
880 | @code{N_RBRAC} stabs. | |
881 | ||
882 | @node Global Variables | |
883 | @section Global Variables | |
884 | ||
885 | @findex N_GSYM | |
886 | @findex C_GSYM | |
887 | @c FIXME: verify for sure that it really is C_GSYM on XCOFF | |
888 | A variable whose scope is not specific to just one source file is | |
889 | represented by the @samp{G} symbol descriptor. These stabs use the | |
890 | @code{N_GSYM} stab type (C_GSYM for XCOFF). The type information for | |
891 | the stab (@pxref{String Field}) gives the type of the variable. | |
892 | ||
893 | For example, the following source code: | |
894 | ||
895 | @example | |
896 | char g_foo = 'c'; | |
897 | @end example | |
898 | ||
899 | @noindent | |
900 | yields the following assembly code: | |
901 | ||
902 | @example | |
903 | .stabs "g_foo:G2",32,0,0,0 # @r{32 is N_GSYM} | |
904 | .global _g_foo | |
905 | .data | |
906 | _g_foo: | |
907 | .byte 99 | |
908 | @end example | |
909 | ||
910 | The address of the variable represented by the @code{N_GSYM} is not | |
911 | contained in the @code{N_GSYM} stab. The debugger gets this information | |
912 | from the external symbol for the global variable. In the example above, | |
913 | the @code{.global _g_foo} and @code{_g_foo:} lines tell the assembler to | |
914 | produce an external symbol. | |
915 | ||
916 | Some compilers, like GCC, output @code{N_GSYM} stabs only once, where | |
917 | the variable is defined. Other compilers, like SunOS4 /bin/cc, output a | |
918 | @code{N_GSYM} stab for each compilation unit which references the | |
919 | variable. | |
920 | ||
921 | @node Register Variables | |
922 | @section Register Variables | |
923 | ||
924 | @findex N_RSYM | |
925 | @findex C_RSYM | |
926 | @c According to an old version of this manual, AIX uses C_RPSYM instead | |
927 | @c of C_RSYM. I am skeptical; this should be verified. | |
928 | Register variables have their own stab type, @code{N_RSYM} | |
929 | (@code{C_RSYM} for XCOFF), and their own symbol descriptor, @samp{r}. | |
930 | The stab's value is the number of the register where the variable data | |
931 | will be stored. | |
932 | @c .stabs "name:type",N_RSYM,0,RegSize,RegNumber (Sun doc) | |
933 | ||
934 | AIX defines a separate symbol descriptor @samp{d} for floating point | |
935 | registers. This seems unnecessary; why not just just give floating | |
936 | point registers different register numbers? I have not verified whether | |
937 | the compiler actually uses @samp{d}. | |
938 | ||
939 | If the register is explicitly allocated to a global variable, but not | |
940 | initialized, as in: | |
941 | ||
942 | @example | |
943 | register int g_bar asm ("%g5"); | |
944 | @end example | |
945 | ||
946 | @noindent | |
947 | then the stab may be emitted at the end of the object file, with | |
948 | the other bss symbols. | |
949 | ||
950 | @node Common Blocks | |
951 | @section Common Blocks | |
952 | ||
953 | A common block is a statically allocated section of memory which can be | |
954 | referred to by several source files. It may contain several variables. | |
955 | I believe Fortran is the only language with this feature. | |
956 | ||
957 | @findex N_BCOMM | |
958 | @findex N_ECOMM | |
959 | @findex C_BCOMM | |
960 | @findex C_ECOMM | |
961 | A @code{N_BCOMM} stab begins a common block and an @code{N_ECOMM} stab | |
962 | ends it. The only field that is significant in these two stabs is the | |
963 | string, which names a normal (non-debugging) symbol that gives the | |
964 | address of the common block. According to IBM documentation, only the | |
965 | @code{N_BCOMM} has the name of the common block (even though their | |
966 | compiler actually puts it both places). | |
967 | ||
968 | @findex N_ECOML | |
969 | @findex C_ECOML | |
970 | The stabs for the members of the common block are between the | |
971 | @code{N_BCOMM} and the @code{N_ECOMM}; the value of each stab is the | |
972 | offset within the common block of that variable. IBM uses the | |
973 | @code{C_ECOML} stab type, and there is a corresponding @code{N_ECOML} | |
974 | stab type, but Sun's Fortran compiler uses @code{N_GSYM} instead. The | |
975 | variables within a common block use the @samp{V} symbol descriptor (I | |
976 | believe this is true of all Fortran variables). Other stabs (at least | |
977 | type declarations using @code{C_DECL}) can also be between the | |
978 | @code{N_BCOMM} and the @code{N_ECOMM}. | |
979 | ||
980 | @node Statics | |
981 | @section Static Variables | |
982 | ||
983 | Initialized static variables are represented by the @samp{S} and | |
984 | @samp{V} symbol descriptors. @samp{S} means file scope static, and | |
985 | @samp{V} means procedure scope static. One exception: in XCOFF, IBM's | |
986 | xlc compiler always uses @samp{V}, and whether it is file scope or not | |
987 | is distinguished by whether the stab is located within a function. | |
988 | ||
989 | @c This is probably not worth mentioning; it is only true on the sparc | |
990 | @c for `double' variables which although declared const are actually in | |
991 | @c the data segment (the text segment can't guarantee 8 byte alignment). | |
992 | @c (although GCC | |
993 | @c 2.4.5 has a bug in that it uses @code{N_FUN}, so neither dbx nor GDB can | |
994 | @c find the variables) | |
995 | @findex N_STSYM | |
996 | @findex N_LCSYM | |
997 | @findex N_FUN, for variables | |
998 | @findex N_ROSYM | |
999 | In a.out files, @code{N_STSYM} means the data section, @code{N_FUN} | |
1000 | means the text section, and @code{N_LCSYM} means the bss section. For | |
1001 | those systems with a read-only data section separate from the text | |
1002 | section (Solaris), @code{N_ROSYM} means the read-only data section. | |
1003 | ||
1004 | For example, the source lines: | |
1005 | ||
1006 | @example | |
1007 | static const int var_const = 5; | |
1008 | static int var_init = 2; | |
1009 | static int var_noinit; | |
1010 | @end example | |
1011 | ||
1012 | @noindent | |
1013 | yield the following stabs: | |
1014 | ||
1015 | @example | |
1016 | .stabs "var_const:S1",36,0,0,_var_const # @r{36 is N_FUN} | |
1017 | @dots{} | |
1018 | .stabs "var_init:S1",38,0,0,_var_init # @r{38 is N_STSYM} | |
1019 | @dots{} | |
1020 | .stabs "var_noinit:S1",40,0,0,_var_noinit # @r{40 is N_LCSYM} | |
1021 | @end example | |
1022 | ||
1023 | @findex C_STSYM | |
1024 | @findex C_BSTAT | |
1025 | @findex C_ESTAT | |
1026 | In XCOFF files, the stab type need not indicate the section; | |
1027 | @code{C_STSYM} can be used for all statics. Also, each static variable | |
1028 | is enclosed in a static block. A @code{C_BSTAT} (emitted with a | |
1029 | @samp{.bs} assembler directive) symbol begins the static block; its | |
1030 | value is the symbol number of the csect symbol whose value is the | |
1031 | address of the static block, its section is the section of the variables | |
1032 | in that static block, and its name is @samp{.bs}. A @code{C_ESTAT} | |
1033 | (emitted with a @samp{.es} assembler directive) symbol ends the static | |
1034 | block; its name is @samp{.es} and its value and section are ignored. | |
1035 | ||
1036 | In ECOFF files, the storage class is used to specify the section, so the | |
1037 | stab type need not indicate the section. | |
1038 | ||
1039 | In ELF files, for the SunPRO compiler version 2.0.1, symbol descriptor | |
1040 | @samp{S} means that the address is absolute (the linker relocates it) | |
1041 | and symbol descriptor @samp{V} means that the address is relative to the | |
1042 | start of the relevant section for that compilation unit. SunPRO has | |
1043 | plans to have the linker stop relocating stabs; I suspect that their the | |
1044 | debugger gets the address from the corresponding ELF (not stab) symbol. | |
1045 | I'm not sure how to find which symbol of that name is the right one. | |
1046 | The clean way to do all this would be to have a the value of a symbol | |
1047 | descriptor @samp{S} symbol be an offset relative to the start of the | |
1048 | file, just like everything else, but that introduces obvious | |
1049 | compatibility problems. For more information on linker stab relocation, | |
1050 | @xref{ELF Linker Relocation}. | |
1051 | ||
1052 | @node Based Variables | |
1053 | @section Fortran Based Variables | |
1054 | ||
1055 | Fortran (at least, the Sun and SGI dialects of FORTRAN-77) has a feature | |
1056 | which allows allocating arrays with @code{malloc}, but which avoids | |
1057 | blurring the line between arrays and pointers the way that C does. In | |
1058 | stabs such a variable uses the @samp{b} symbol descriptor. | |
1059 | ||
1060 | For example, the Fortran declarations | |
1061 | ||
1062 | @example | |
1063 | real foo, foo10(10), foo10_5(10,5) | |
1064 | pointer (foop, foo) | |
1065 | pointer (foo10p, foo10) | |
1066 | pointer (foo105p, foo10_5) | |
1067 | @end example | |
1068 | ||
1069 | produce the stabs | |
1070 | ||
1071 | @example | |
1072 | foo:b6 | |
1073 | foo10:bar3;1;10;6 | |
1074 | foo10_5:bar3;1;5;ar3;1;10;6 | |
1075 | @end example | |
1076 | ||
1077 | In this example, @code{real} is type 6 and type 3 is an integral type | |
1078 | which is the type of the subscripts of the array (probably | |
1079 | @code{integer}). | |
1080 | ||
1081 | The @samp{b} symbol descriptor is like @samp{V} in that it denotes a | |
1082 | statically allocated symbol whose scope is local to a function; see | |
1083 | @xref{Statics}. The value of the symbol, instead of being the address | |
1084 | of the variable itself, is the address of a pointer to that variable. | |
1085 | So in the above example, the value of the @code{foo} stab is the address | |
1086 | of a pointer to a real, the value of the @code{foo10} stab is the | |
1087 | address of a pointer to a 10-element array of reals, and the value of | |
1088 | the @code{foo10_5} stab is the address of a pointer to a 5-element array | |
1089 | of 10-element arrays of reals. | |
1090 | ||
1091 | @node Parameters | |
1092 | @section Parameters | |
1093 | ||
1094 | Formal parameters to a function are represented by a stab (or sometimes | |
1095 | two; see below) for each parameter. The stabs are in the order in which | |
1096 | the debugger should print the parameters (i.e., the order in which the | |
1097 | parameters are declared in the source file). The exact form of the stab | |
1098 | depends on how the parameter is being passed. | |
1099 | ||
1100 | @findex N_PSYM | |
1101 | @findex C_PSYM | |
1102 | Parameters passed on the stack use the symbol descriptor @samp{p} and | |
1103 | the @code{N_PSYM} symbol type (or @code{C_PSYM} for XCOFF). The value | |
1104 | of the symbol is an offset used to locate the parameter on the stack; | |
1105 | its exact meaning is machine-dependent, but on most machines it is an | |
1106 | offset from the frame pointer. | |
1107 | ||
1108 | As a simple example, the code: | |
1109 | ||
1110 | @example | |
1111 | main (argc, argv) | |
1112 | int argc; | |
1113 | char **argv; | |
1114 | @end example | |
1115 | ||
1116 | produces the stabs: | |
1117 | ||
1118 | @example | |
1119 | .stabs "main:F1",36,0,0,_main # @r{36 is N_FUN} | |
1120 | .stabs "argc:p1",160,0,0,68 # @r{160 is N_PSYM} | |
1121 | .stabs "argv:p20=*21=*2",160,0,0,72 | |
1122 | @end example | |
1123 | ||
1124 | The type definition of @code{argv} is interesting because it contains | |
1125 | several type definitions. Type 21 is pointer to type 2 (char) and | |
1126 | @code{argv} (type 20) is pointer to type 21. | |
1127 | ||
1128 | @c FIXME: figure out what these mean and describe them coherently. | |
1129 | The following symbol descriptors are also said to go with @code{N_PSYM}. | |
1130 | The value of the symbol is said to be an offset from the argument | |
1131 | pointer (I'm not sure whether this is true or not). | |
1132 | ||
1133 | @example | |
1134 | pP (<<??>>) | |
1135 | pF Fortran function parameter | |
1136 | X (function result variable) | |
1137 | @end example | |
1138 | ||
1139 | @menu | |
1140 | * Register Parameters:: | |
1141 | * Local Variable Parameters:: | |
1142 | * Reference Parameters:: | |
1143 | * Conformant Arrays:: | |
1144 | @end menu | |
1145 | ||
1146 | @node Register Parameters | |
1147 | @subsection Passing Parameters in Registers | |
1148 | ||
1149 | If the parameter is passed in a register, then traditionally there are | |
1150 | two symbols for each argument: | |
1151 | ||
1152 | @example | |
1153 | .stabs "arg:p1" . . . ; N_PSYM | |
1154 | .stabs "arg:r1" . . . ; N_RSYM | |
1155 | @end example | |
1156 | ||
1157 | Debuggers use the second one to find the value, and the first one to | |
1158 | know that it is an argument. | |
1159 | ||
1160 | @findex C_RPSYM | |
1161 | @findex N_RSYM, for parameters | |
1162 | Because that approach is kind of ugly, some compilers use symbol | |
1163 | descriptor @samp{P} or @samp{R} to indicate an argument which is in a | |
1164 | register. Symbol type @code{C_RPSYM} is used in XCOFF and @code{N_RSYM} | |
1165 | is used otherwise. The symbol's value is the register number. @samp{P} | |
1166 | and @samp{R} mean the same thing; the difference is that @samp{P} is a | |
1167 | GNU invention and @samp{R} is an IBM (XCOFF) invention. As of version | |
1168 | 4.9, GDB should handle either one. | |
1169 | ||
1170 | There is at least one case where GCC uses a @samp{p} and @samp{r} pair | |
1171 | rather than @samp{P}; this is where the argument is passed in the | |
1172 | argument list and then loaded into a register. | |
1173 | ||
1174 | According to the AIX documentation, symbol descriptor @samp{D} is for a | |
1175 | parameter passed in a floating point register. This seems | |
1176 | unnecessary---why not just use @samp{R} with a register number which | |
1177 | indicates that it's a floating point register? I haven't verified | |
1178 | whether the system actually does what the documentation indicates. | |
1179 | ||
1180 | @c FIXME: On the hppa this is for any type > 8 bytes, I think, and not | |
1181 | @c for small structures (investigate). | |
1182 | On the sparc and hppa, for a @samp{P} symbol whose type is a structure | |
1183 | or union, the register contains the address of the structure. On the | |
1184 | sparc, this is also true of a @samp{p} and @samp{r} pair (using Sun | |
1185 | @code{cc}) or a @samp{p} symbol. However, if a (small) structure is | |
1186 | really in a register, @samp{r} is used. And, to top it all off, on the | |
1187 | hppa it might be a structure which was passed on the stack and loaded | |
1188 | into a register and for which there is a @samp{p} and @samp{r} pair! I | |
1189 | believe that symbol descriptor @samp{i} is supposed to deal with this | |
1190 | case (it is said to mean "value parameter by reference, indirect | |
1191 | access"; I don't know the source for this information), but I don't know | |
1192 | details or what compilers or debuggers use it, if any (not GDB or GCC). | |
1193 | It is not clear to me whether this case needs to be dealt with | |
1194 | differently than parameters passed by reference (@pxref{Reference Parameters}). | |
1195 | ||
1196 | @node Local Variable Parameters | |
1197 | @subsection Storing Parameters as Local Variables | |
1198 | ||
1199 | There is a case similar to an argument in a register, which is an | |
1200 | argument that is actually stored as a local variable. Sometimes this | |
1201 | happens when the argument was passed in a register and then the compiler | |
1202 | stores it as a local variable. If possible, the compiler should claim | |
1203 | that it's in a register, but this isn't always done. | |
1204 | ||
1205 | If a parameter is passed as one type and converted to a smaller type by | |
1206 | the prologue (for example, the parameter is declared as a @code{float}, | |
1207 | but the calling conventions specify that it is passed as a | |
1208 | @code{double}), then GCC2 (sometimes) uses a pair of symbols. The first | |
1209 | symbol uses symbol descriptor @samp{p} and the type which is passed. | |
1210 | The second symbol has the type and location which the parameter actually | |
1211 | has after the prologue. For example, suppose the following C code | |
1212 | appears with no prototypes involved: | |
1213 | ||
1214 | @example | |
1215 | void | |
1216 | subr (f) | |
1217 | float f; | |
1218 | @{ | |
1219 | @end example | |
1220 | ||
1221 | if @code{f} is passed as a double at stack offset 8, and the prologue | |
1222 | converts it to a float in register number 0, then the stabs look like: | |
1223 | ||
1224 | @example | |
1225 | .stabs "f:p13",160,0,3,8 # @r{160 is @code{N_PSYM}, here 13 is @code{double}} | |
1226 | .stabs "f:r12",64,0,3,0 # @r{64 is @code{N_RSYM}, here 12 is @code{float}} | |
1227 | @end example | |
1228 | ||
1229 | In both stabs 3 is the line number where @code{f} is declared | |
1230 | (@pxref{Line Numbers}). | |
1231 | ||
1232 | @findex N_LSYM, for parameter | |
1233 | GCC, at least on the 960, has another solution to the same problem. It | |
1234 | uses a single @samp{p} symbol descriptor for an argument which is stored | |
1235 | as a local variable but uses @code{N_LSYM} instead of @code{N_PSYM}. In | |
1236 | this case, the value of the symbol is an offset relative to the local | |
1237 | variables for that function, not relative to the arguments; on some | |
1238 | machines those are the same thing, but not on all. | |
1239 | ||
1240 | @c This is mostly just background info; the part that logically belongs | |
1241 | @c here is the last sentence. | |
1242 | On the VAX or on other machines in which the calling convention includes | |
1243 | the number of words of arguments actually passed, the debugger (GDB at | |
1244 | least) uses the parameter symbols to keep track of whether it needs to | |
1245 | print nameless arguments in addition to the formal parameters which it | |
1246 | has printed because each one has a stab. For example, in | |
1247 | ||
1248 | @example | |
1249 | extern int fprintf (FILE *stream, char *format, @dots{}); | |
1250 | @dots{} | |
1251 | fprintf (stdout, "%d\n", x); | |
1252 | @end example | |
1253 | ||
1254 | there are stabs for @code{stream} and @code{format}. On most machines, | |
1255 | the debugger can only print those two arguments (because it has no way | |
1256 | of knowing that additional arguments were passed), but on the VAX or | |
1257 | other machines with a calling convention which indicates the number of | |
1258 | words of arguments, the debugger can print all three arguments. To do | |
1259 | so, the parameter symbol (symbol descriptor @samp{p}) (not necessarily | |
1260 | @samp{r} or symbol descriptor omitted symbols) needs to contain the | |
1261 | actual type as passed (for example, @code{double} not @code{float} if it | |
1262 | is passed as a double and converted to a float). | |
1263 | ||
1264 | @node Reference Parameters | |
1265 | @subsection Passing Parameters by Reference | |
1266 | ||
1267 | If the parameter is passed by reference (e.g., Pascal @code{VAR} | |
1268 | parameters), then the symbol descriptor is @samp{v} if it is in the | |
1269 | argument list, or @samp{a} if it in a register. Other than the fact | |
1270 | that these contain the address of the parameter rather than the | |
1271 | parameter itself, they are identical to @samp{p} and @samp{R}, | |
1272 | respectively. I believe @samp{a} is an AIX invention; @samp{v} is | |
1273 | supported by all stabs-using systems as far as I know. | |
1274 | ||
1275 | @node Conformant Arrays | |
1276 | @subsection Passing Conformant Array Parameters | |
1277 | ||
1278 | @c Is this paragraph correct? It is based on piecing together patchy | |
1279 | @c information and some guesswork | |
1280 | Conformant arrays are a feature of Modula-2, and perhaps other | |
1281 | languages, in which the size of an array parameter is not known to the | |
1282 | called function until run-time. Such parameters have two stabs: a | |
1283 | @samp{x} for the array itself, and a @samp{C}, which represents the size | |
1284 | of the array. The value of the @samp{x} stab is the offset in the | |
1285 | argument list where the address of the array is stored (it this right? | |
1286 | it is a guess); the value of the @samp{C} stab is the offset in the | |
1287 | argument list where the size of the array (in elements? in bytes?) is | |
1288 | stored. | |
1289 | ||
1290 | @node Types | |
1291 | @chapter Defining Types | |
1292 | ||
1293 | The examples so far have described types as references to previously | |
1294 | defined types, or defined in terms of subranges of or pointers to | |
1295 | previously defined types. This chapter describes the other type | |
1296 | descriptors that may follow the @samp{=} in a type definition. | |
1297 | ||
1298 | @menu | |
1299 | * Builtin Types:: Integers, floating point, void, etc. | |
1300 | * Miscellaneous Types:: Pointers, sets, files, etc. | |
1301 | * Cross-References:: Referring to a type not yet defined. | |
1302 | * Subranges:: A type with a specific range. | |
1303 | * Arrays:: An aggregate type of same-typed elements. | |
1304 | * Strings:: Like an array but also has a length. | |
1305 | * Enumerations:: Like an integer but the values have names. | |
1306 | * Structures:: An aggregate type of different-typed elements. | |
1307 | * Typedefs:: Giving a type a name. | |
1308 | * Unions:: Different types sharing storage. | |
1309 | * Function Types:: | |
1310 | @end menu | |
1311 | ||
1312 | @node Builtin Types | |
1313 | @section Builtin Types | |
1314 | ||
1315 | Certain types are built in (@code{int}, @code{short}, @code{void}, | |
1316 | @code{float}, etc.); the debugger recognizes these types and knows how | |
1317 | to handle them. Thus, don't be surprised if some of the following ways | |
1318 | of specifying builtin types do not specify everything that a debugger | |
1319 | would need to know about the type---in some cases they merely specify | |
1320 | enough information to distinguish the type from other types. | |
1321 | ||
bd79f757 | 1322 | The traditional way to define builtin types is convoluted, so new ways |
c906108c SS |
1323 | have been invented to describe them. Sun's @code{acc} uses special |
1324 | builtin type descriptors (@samp{b} and @samp{R}), and IBM uses negative | |
1325 | type numbers. GDB accepts all three ways, as of version 4.8; dbx just | |
1326 | accepts the traditional builtin types and perhaps one of the other two | |
1327 | formats. The following sections describe each of these formats. | |
1328 | ||
1329 | @menu | |
bd79f757 | 1330 | * Traditional Builtin Types:: Put on your seat belts and prepare for kludgery |
c906108c SS |
1331 | * Builtin Type Descriptors:: Builtin types with special type descriptors |
1332 | * Negative Type Numbers:: Builtin types using negative type numbers | |
1333 | @end menu | |
1334 | ||
1335 | @node Traditional Builtin Types | |
1336 | @subsection Traditional Builtin Types | |
1337 | ||
1338 | This is the traditional, convoluted method for defining builtin types. | |
1339 | There are several classes of such type definitions: integer, floating | |
1340 | point, and @code{void}. | |
1341 | ||
1342 | @menu | |
1343 | * Traditional Integer Types:: | |
1344 | * Traditional Other Types:: | |
1345 | @end menu | |
1346 | ||
1347 | @node Traditional Integer Types | |
1348 | @subsubsection Traditional Integer Types | |
1349 | ||
1350 | Often types are defined as subranges of themselves. If the bounding values | |
1351 | fit within an @code{int}, then they are given normally. For example: | |
1352 | ||
1353 | @example | |
1354 | .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0 # @r{128 is N_LSYM} | |
1355 | .stabs "char:t2=r2;0;127;",128,0,0,0 | |
1356 | @end example | |
1357 | ||
1358 | Builtin types can also be described as subranges of @code{int}: | |
1359 | ||
1360 | @example | |
1361 | .stabs "unsigned short:t6=r1;0;65535;",128,0,0,0 | |
1362 | @end example | |
1363 | ||
1364 | If the lower bound of a subrange is 0 and the upper bound is -1, | |
1365 | the type is an unsigned integral type whose bounds are too | |
1366 | big to describe in an @code{int}. Traditionally this is only used for | |
1367 | @code{unsigned int} and @code{unsigned long}: | |
1368 | ||
1369 | @example | |
1370 | .stabs "unsigned int:t4=r1;0;-1;",128,0,0,0 | |
1371 | @end example | |
1372 | ||
1373 | For larger types, GCC 2.4.5 puts out bounds in octal, with one or more | |
1374 | leading zeroes. In this case a negative bound consists of a number | |
1375 | which is a 1 bit (for the sign bit) followed by a 0 bit for each bit in | |
1376 | the number (except the sign bit), and a positive bound is one which is a | |
1377 | 1 bit for each bit in the number (except possibly the sign bit). All | |
1378 | known versions of dbx and GDB version 4 accept this (at least in the | |
1379 | sense of not refusing to process the file), but GDB 3.5 refuses to read | |
1380 | the whole file containing such symbols. So GCC 2.3.3 did not output the | |
1381 | proper size for these types. As an example of octal bounds, the string | |
1382 | fields of the stabs for 64 bit integer types look like: | |
1383 | ||
1384 | @c .stabs directives, etc., omitted to make it fit on the page. | |
1385 | @example | |
1386 | long int:t3=r1;001000000000000000000000;000777777777777777777777; | |
1387 | long unsigned int:t5=r1;000000000000000000000000;001777777777777777777777; | |
1388 | @end example | |
1389 | ||
1390 | If the lower bound of a subrange is 0 and the upper bound is negative, | |
1391 | the type is an unsigned integral type whose size in bytes is the | |
1392 | absolute value of the upper bound. I believe this is a Convex | |
1393 | convention for @code{unsigned long long}. | |
1394 | ||
1395 | If the lower bound of a subrange is negative and the upper bound is 0, | |
1396 | the type is a signed integral type whose size in bytes is | |
1397 | the absolute value of the lower bound. I believe this is a Convex | |
1398 | convention for @code{long long}. To distinguish this from a legitimate | |
1399 | subrange, the type should be a subrange of itself. I'm not sure whether | |
1400 | this is the case for Convex. | |
1401 | ||
1402 | @node Traditional Other Types | |
1403 | @subsubsection Traditional Other Types | |
1404 | ||
1405 | If the upper bound of a subrange is 0 and the lower bound is positive, | |
1406 | the type is a floating point type, and the lower bound of the subrange | |
1407 | indicates the number of bytes in the type: | |
1408 | ||
1409 | @example | |
1410 | .stabs "float:t12=r1;4;0;",128,0,0,0 | |
1411 | .stabs "double:t13=r1;8;0;",128,0,0,0 | |
1412 | @end example | |
1413 | ||
1414 | However, GCC writes @code{long double} the same way it writes | |
1415 | @code{double}, so there is no way to distinguish. | |
1416 | ||
1417 | @example | |
1418 | .stabs "long double:t14=r1;8;0;",128,0,0,0 | |
1419 | @end example | |
1420 | ||
1421 | Complex types are defined the same way as floating-point types; there is | |
1422 | no way to distinguish a single-precision complex from a double-precision | |
1423 | floating-point type. | |
1424 | ||
1425 | The C @code{void} type is defined as itself: | |
1426 | ||
1427 | @example | |
1428 | .stabs "void:t15=15",128,0,0,0 | |
1429 | @end example | |
1430 | ||
1431 | I'm not sure how a boolean type is represented. | |
1432 | ||
1433 | @node Builtin Type Descriptors | |
1434 | @subsection Defining Builtin Types Using Builtin Type Descriptors | |
1435 | ||
1436 | This is the method used by Sun's @code{acc} for defining builtin types. | |
1437 | These are the type descriptors to define builtin types: | |
1438 | ||
1439 | @table @code | |
1440 | @c FIXME: clean up description of width and offset, once we figure out | |
1441 | @c what they mean | |
1442 | @item b @var{signed} @var{char-flag} @var{width} ; @var{offset} ; @var{nbits} ; | |
1443 | Define an integral type. @var{signed} is @samp{u} for unsigned or | |
1444 | @samp{s} for signed. @var{char-flag} is @samp{c} which indicates this | |
1445 | is a character type, or is omitted. I assume this is to distinguish an | |
1446 | integral type from a character type of the same size, for example it | |
1447 | might make sense to set it for the C type @code{wchar_t} so the debugger | |
1448 | can print such variables differently (Solaris does not do this). Sun | |
1449 | sets it on the C types @code{signed char} and @code{unsigned char} which | |
1450 | arguably is wrong. @var{width} and @var{offset} appear to be for small | |
1451 | objects stored in larger ones, for example a @code{short} in an | |
1452 | @code{int} register. @var{width} is normally the number of bytes in the | |
1453 | type. @var{offset} seems to always be zero. @var{nbits} is the number | |
1454 | of bits in the type. | |
1455 | ||
1456 | Note that type descriptor @samp{b} used for builtin types conflicts with | |
1457 | its use for Pascal space types (@pxref{Miscellaneous Types}); they can | |
1458 | be distinguished because the character following the type descriptor | |
1459 | will be a digit, @samp{(}, or @samp{-} for a Pascal space type, or | |
1460 | @samp{u} or @samp{s} for a builtin type. | |
1461 | ||
1462 | @item w | |
1463 | Documented by AIX to define a wide character type, but their compiler | |
1464 | actually uses negative type numbers (@pxref{Negative Type Numbers}). | |
1465 | ||
1466 | @item R @var{fp-type} ; @var{bytes} ; | |
1467 | Define a floating point type. @var{fp-type} has one of the following values: | |
1468 | ||
1469 | @table @code | |
1470 | @item 1 (NF_SINGLE) | |
1471 | IEEE 32-bit (single precision) floating point format. | |
1472 | ||
1473 | @item 2 (NF_DOUBLE) | |
1474 | IEEE 64-bit (double precision) floating point format. | |
1475 | ||
1476 | @item 3 (NF_COMPLEX) | |
1477 | @item 4 (NF_COMPLEX16) | |
1478 | @item 5 (NF_COMPLEX32) | |
1479 | @c "GDB source" really means @file{include/aout/stab_gnu.h}, but trying | |
1480 | @c to put that here got an overfull hbox. | |
1481 | These are for complex numbers. A comment in the GDB source describes | |
1482 | them as Fortran @code{complex}, @code{double complex}, and | |
1483 | @code{complex*16}, respectively, but what does that mean? (i.e., Single | |
bd79f757 | 1484 | precision? Double precision?). |
c906108c SS |
1485 | |
1486 | @item 6 (NF_LDOUBLE) | |
1487 | Long double. This should probably only be used for Sun format | |
1488 | @code{long double}, and new codes should be used for other floating | |
1489 | point formats (@code{NF_DOUBLE} can be used if a @code{long double} is | |
1490 | really just an IEEE double, of course). | |
1491 | @end table | |
1492 | ||
1493 | @var{bytes} is the number of bytes occupied by the type. This allows a | |
1494 | debugger to perform some operations with the type even if it doesn't | |
1495 | understand @var{fp-type}. | |
1496 | ||
1497 | @item g @var{type-information} ; @var{nbits} | |
1498 | Documented by AIX to define a floating type, but their compiler actually | |
1499 | uses negative type numbers (@pxref{Negative Type Numbers}). | |
1500 | ||
1501 | @item c @var{type-information} ; @var{nbits} | |
1502 | Documented by AIX to define a complex type, but their compiler actually | |
1503 | uses negative type numbers (@pxref{Negative Type Numbers}). | |
1504 | @end table | |
1505 | ||
1506 | The C @code{void} type is defined as a signed integral type 0 bits long: | |
1507 | @example | |
1508 | .stabs "void:t19=bs0;0;0",128,0,0,0 | |
1509 | @end example | |
1510 | The Solaris compiler seems to omit the trailing semicolon in this case. | |
1511 | Getting sloppy in this way is not a swift move because if a type is | |
1512 | embedded in a more complex expression it is necessary to be able to tell | |
1513 | where it ends. | |
1514 | ||
1515 | I'm not sure how a boolean type is represented. | |
1516 | ||
1517 | @node Negative Type Numbers | |
1518 | @subsection Negative Type Numbers | |
1519 | ||
1520 | This is the method used in XCOFF for defining builtin types. | |
1521 | Since the debugger knows about the builtin types anyway, the idea of | |
1522 | negative type numbers is simply to give a special type number which | |
1523 | indicates the builtin type. There is no stab defining these types. | |
1524 | ||
1525 | There are several subtle issues with negative type numbers. | |
1526 | ||
1527 | One is the size of the type. A builtin type (for example the C types | |
1528 | @code{int} or @code{long}) might have different sizes depending on | |
1529 | compiler options, the target architecture, the ABI, etc. This issue | |
1530 | doesn't come up for IBM tools since (so far) they just target the | |
1531 | RS/6000; the sizes indicated below for each size are what the IBM | |
1532 | RS/6000 tools use. To deal with differing sizes, either define separate | |
1533 | negative type numbers for each size (which works but requires changing | |
1534 | the debugger, and, unless you get both AIX dbx and GDB to accept the | |
1535 | change, introduces an incompatibility), or use a type attribute | |
1536 | (@pxref{String Field}) to define a new type with the appropriate size | |
1537 | (which merely requires a debugger which understands type attributes, | |
1538 | like AIX dbx or GDB). For example, | |
1539 | ||
1540 | @example | |
1541 | .stabs "boolean:t10=@@s8;-16",128,0,0,0 | |
1542 | @end example | |
1543 | ||
1544 | defines an 8-bit boolean type, and | |
1545 | ||
1546 | @example | |
1547 | .stabs "boolean:t10=@@s64;-16",128,0,0,0 | |
1548 | @end example | |
1549 | ||
1550 | defines a 64-bit boolean type. | |
1551 | ||
1552 | A similar issue is the format of the type. This comes up most often for | |
1553 | floating-point types, which could have various formats (particularly | |
1554 | extended doubles, which vary quite a bit even among IEEE systems). | |
1555 | Again, it is best to define a new negative type number for each | |
1556 | different format; changing the format based on the target system has | |
1557 | various problems. One such problem is that the Alpha has both VAX and | |
1558 | IEEE floating types. One can easily imagine one library using the VAX | |
1559 | types and another library in the same executable using the IEEE types. | |
1560 | Another example is that the interpretation of whether a boolean is true | |
1561 | or false can be based on the least significant bit, most significant | |
1562 | bit, whether it is zero, etc., and different compilers (or different | |
1563 | options to the same compiler) might provide different kinds of boolean. | |
1564 | ||
1565 | The last major issue is the names of the types. The name of a given | |
1566 | type depends @emph{only} on the negative type number given; these do not | |
1567 | vary depending on the language, the target system, or anything else. | |
1568 | One can always define separate type numbers---in the following list you | |
1569 | will see for example separate @code{int} and @code{integer*4} types | |
1570 | which are identical except for the name. But compatibility can be | |
1571 | maintained by not inventing new negative type numbers and instead just | |
1572 | defining a new type with a new name. For example: | |
1573 | ||
1574 | @example | |
1575 | .stabs "CARDINAL:t10=-8",128,0,0,0 | |
1576 | @end example | |
1577 | ||
1578 | Here is the list of negative type numbers. The phrase @dfn{integral | |
1579 | type} is used to mean twos-complement (I strongly suspect that all | |
1580 | machines which use stabs use twos-complement; most machines use | |
1581 | twos-complement these days). | |
1582 | ||
1583 | @table @code | |
1584 | @item -1 | |
1585 | @code{int}, 32 bit signed integral type. | |
1586 | ||
1587 | @item -2 | |
1588 | @code{char}, 8 bit type holding a character. Both GDB and dbx on AIX | |
1589 | treat this as signed. GCC uses this type whether @code{char} is signed | |
1590 | or not, which seems like a bad idea. The AIX compiler (@code{xlc}) seems to | |
1591 | avoid this type; it uses -5 instead for @code{char}. | |
1592 | ||
1593 | @item -3 | |
1594 | @code{short}, 16 bit signed integral type. | |
1595 | ||
1596 | @item -4 | |
1597 | @code{long}, 32 bit signed integral type. | |
1598 | ||
1599 | @item -5 | |
1600 | @code{unsigned char}, 8 bit unsigned integral type. | |
1601 | ||
1602 | @item -6 | |
1603 | @code{signed char}, 8 bit signed integral type. | |
1604 | ||
1605 | @item -7 | |
1606 | @code{unsigned short}, 16 bit unsigned integral type. | |
1607 | ||
1608 | @item -8 | |
1609 | @code{unsigned int}, 32 bit unsigned integral type. | |
1610 | ||
1611 | @item -9 | |
1612 | @code{unsigned}, 32 bit unsigned integral type. | |
1613 | ||
1614 | @item -10 | |
1615 | @code{unsigned long}, 32 bit unsigned integral type. | |
1616 | ||
1617 | @item -11 | |
1618 | @code{void}, type indicating the lack of a value. | |
1619 | ||
1620 | @item -12 | |
1621 | @code{float}, IEEE single precision. | |
1622 | ||
1623 | @item -13 | |
1624 | @code{double}, IEEE double precision. | |
1625 | ||
1626 | @item -14 | |
1627 | @code{long double}, IEEE double precision. The compiler claims the size | |
1628 | will increase in a future release, and for binary compatibility you have | |
1629 | to avoid using @code{long double}. I hope when they increase it they | |
1630 | use a new negative type number. | |
1631 | ||
1632 | @item -15 | |
1633 | @code{integer}. 32 bit signed integral type. | |
1634 | ||
1635 | @item -16 | |
1636 | @code{boolean}. 32 bit type. GDB and GCC assume that zero is false, | |
1637 | one is true, and other values have unspecified meaning. I hope this | |
1638 | agrees with how the IBM tools use the type. | |
1639 | ||
1640 | @item -17 | |
1641 | @code{short real}. IEEE single precision. | |
1642 | ||
1643 | @item -18 | |
1644 | @code{real}. IEEE double precision. | |
1645 | ||
1646 | @item -19 | |
1647 | @code{stringptr}. @xref{Strings}. | |
1648 | ||
1649 | @item -20 | |
1650 | @code{character}, 8 bit unsigned character type. | |
1651 | ||
1652 | @item -21 | |
1653 | @code{logical*1}, 8 bit type. This Fortran type has a split | |
1654 | personality in that it is used for boolean variables, but can also be | |
1655 | used for unsigned integers. 0 is false, 1 is true, and other values are | |
1656 | non-boolean. | |
1657 | ||
1658 | @item -22 | |
1659 | @code{logical*2}, 16 bit type. This Fortran type has a split | |
1660 | personality in that it is used for boolean variables, but can also be | |
1661 | used for unsigned integers. 0 is false, 1 is true, and other values are | |
1662 | non-boolean. | |
1663 | ||
1664 | @item -23 | |
1665 | @code{logical*4}, 32 bit type. This Fortran type has a split | |
1666 | personality in that it is used for boolean variables, but can also be | |
1667 | used for unsigned integers. 0 is false, 1 is true, and other values are | |
1668 | non-boolean. | |
1669 | ||
1670 | @item -24 | |
1671 | @code{logical}, 32 bit type. This Fortran type has a split | |
1672 | personality in that it is used for boolean variables, but can also be | |
1673 | used for unsigned integers. 0 is false, 1 is true, and other values are | |
1674 | non-boolean. | |
1675 | ||
1676 | @item -25 | |
1677 | @code{complex}. A complex type consisting of two IEEE single-precision | |
1678 | floating point values. | |
1679 | ||
1680 | @item -26 | |
1681 | @code{complex}. A complex type consisting of two IEEE double-precision | |
1682 | floating point values. | |
1683 | ||
1684 | @item -27 | |
1685 | @code{integer*1}, 8 bit signed integral type. | |
1686 | ||
1687 | @item -28 | |
1688 | @code{integer*2}, 16 bit signed integral type. | |
1689 | ||
1690 | @item -29 | |
1691 | @code{integer*4}, 32 bit signed integral type. | |
1692 | ||
1693 | @item -30 | |
1694 | @code{wchar}. Wide character, 16 bits wide, unsigned (what format? | |
1695 | Unicode?). | |
1696 | ||
1697 | @item -31 | |
1698 | @code{long long}, 64 bit signed integral type. | |
1699 | ||
1700 | @item -32 | |
1701 | @code{unsigned long long}, 64 bit unsigned integral type. | |
1702 | ||
1703 | @item -33 | |
1704 | @code{logical*8}, 64 bit unsigned integral type. | |
1705 | ||
1706 | @item -34 | |
1707 | @code{integer*8}, 64 bit signed integral type. | |
1708 | @end table | |
1709 | ||
1710 | @node Miscellaneous Types | |
1711 | @section Miscellaneous Types | |
1712 | ||
1713 | @table @code | |
1714 | @item b @var{type-information} ; @var{bytes} | |
1715 | Pascal space type. This is documented by IBM; what does it mean? | |
1716 | ||
1717 | This use of the @samp{b} type descriptor can be distinguished | |
1718 | from its use for builtin integral types (@pxref{Builtin Type | |
1719 | Descriptors}) because the character following the type descriptor is | |
1720 | always a digit, @samp{(}, or @samp{-}. | |
1721 | ||
1722 | @item B @var{type-information} | |
1723 | A volatile-qualified version of @var{type-information}. This is | |
1724 | a Sun extension. References and stores to a variable with a | |
1725 | volatile-qualified type must not be optimized or cached; they | |
1726 | must occur as the user specifies them. | |
1727 | ||
1728 | @item d @var{type-information} | |
1729 | File of type @var{type-information}. As far as I know this is only used | |
1730 | by Pascal. | |
1731 | ||
1732 | @item k @var{type-information} | |
1733 | A const-qualified version of @var{type-information}. This is a Sun | |
1734 | extension. A variable with a const-qualified type cannot be modified. | |
1735 | ||
1736 | @item M @var{type-information} ; @var{length} | |
1737 | Multiple instance type. The type seems to composed of @var{length} | |
1738 | repetitions of @var{type-information}, for example @code{character*3} is | |
1739 | represented by @samp{M-2;3}, where @samp{-2} is a reference to a | |
1740 | character type (@pxref{Negative Type Numbers}). I'm not sure how this | |
1741 | differs from an array. This appears to be a Fortran feature. | |
1742 | @var{length} is a bound, like those in range types; see @ref{Subranges}. | |
1743 | ||
1744 | @item S @var{type-information} | |
1745 | Pascal set type. @var{type-information} must be a small type such as an | |
1746 | enumeration or a subrange, and the type is a bitmask whose length is | |
1747 | specified by the number of elements in @var{type-information}. | |
1748 | ||
1749 | In CHILL, if it is a bitstring instead of a set, also use the @samp{S} | |
1750 | type attribute (@pxref{String Field}). | |
1751 | ||
1752 | @item * @var{type-information} | |
1753 | Pointer to @var{type-information}. | |
1754 | @end table | |
1755 | ||
1756 | @node Cross-References | |
1757 | @section Cross-References to Other Types | |
1758 | ||
1759 | A type can be used before it is defined; one common way to deal with | |
1760 | that situation is just to use a type reference to a type which has not | |
1761 | yet been defined. | |
1762 | ||
1763 | Another way is with the @samp{x} type descriptor, which is followed by | |
1764 | @samp{s} for a structure tag, @samp{u} for a union tag, or @samp{e} for | |
1765 | a enumerator tag, followed by the name of the tag, followed by @samp{:}. | |
1766 | If the name contains @samp{::} between a @samp{<} and @samp{>} pair (for | |
1767 | C++ templates), such a @samp{::} does not end the name---only a single | |
1768 | @samp{:} ends the name; see @ref{Nested Symbols}. | |
1769 | ||
1770 | For example, the following C declarations: | |
1771 | ||
1772 | @example | |
1773 | struct foo; | |
1774 | struct foo *bar; | |
1775 | @end example | |
1776 | ||
1777 | @noindent | |
1778 | produce: | |
1779 | ||
1780 | @example | |
1781 | .stabs "bar:G16=*17=xsfoo:",32,0,0,0 | |
1782 | @end example | |
1783 | ||
1784 | Not all debuggers support the @samp{x} type descriptor, so on some | |
1785 | machines GCC does not use it. I believe that for the above example it | |
1786 | would just emit a reference to type 17 and never define it, but I | |
1787 | haven't verified that. | |
1788 | ||
1789 | Modula-2 imported types, at least on AIX, use the @samp{i} type | |
1790 | descriptor, which is followed by the name of the module from which the | |
1791 | type is imported, followed by @samp{:}, followed by the name of the | |
1792 | type. There is then optionally a comma followed by type information for | |
1793 | the type. This differs from merely naming the type (@pxref{Typedefs}) in | |
1794 | that it identifies the module; I don't understand whether the name of | |
1795 | the type given here is always just the same as the name we are giving | |
1796 | it, or whether this type descriptor is used with a nameless stab | |
1797 | (@pxref{String Field}), or what. The symbol ends with @samp{;}. | |
1798 | ||
1799 | @node Subranges | |
1800 | @section Subrange Types | |
1801 | ||
1802 | The @samp{r} type descriptor defines a type as a subrange of another | |
1803 | type. It is followed by type information for the type of which it is a | |
1804 | subrange, a semicolon, an integral lower bound, a semicolon, an | |
1805 | integral upper bound, and a semicolon. The AIX documentation does not | |
1806 | specify the trailing semicolon, in an effort to specify array indexes | |
1807 | more cleanly, but a subrange which is not an array index has always | |
1808 | included a trailing semicolon (@pxref{Arrays}). | |
1809 | ||
1810 | Instead of an integer, either bound can be one of the following: | |
1811 | ||
1812 | @table @code | |
1813 | @item A @var{offset} | |
1814 | The bound is passed by reference on the stack at offset @var{offset} | |
1815 | from the argument list. @xref{Parameters}, for more information on such | |
1816 | offsets. | |
1817 | ||
1818 | @item T @var{offset} | |
1819 | The bound is passed by value on the stack at offset @var{offset} from | |
1820 | the argument list. | |
1821 | ||
1822 | @item a @var{register-number} | |
bd79f757 | 1823 | The bound is passed by reference in register number |
c906108c SS |
1824 | @var{register-number}. |
1825 | ||
1826 | @item t @var{register-number} | |
1827 | The bound is passed by value in register number @var{register-number}. | |
1828 | ||
1829 | @item J | |
1830 | There is no bound. | |
1831 | @end table | |
1832 | ||
1833 | Subranges are also used for builtin types; see @ref{Traditional Builtin Types}. | |
1834 | ||
1835 | @node Arrays | |
1836 | @section Array Types | |
1837 | ||
1838 | Arrays use the @samp{a} type descriptor. Following the type descriptor | |
1839 | is the type of the index and the type of the array elements. If the | |
1840 | index type is a range type, it ends in a semicolon; otherwise | |
1841 | (for example, if it is a type reference), there does not | |
1842 | appear to be any way to tell where the types are separated. In an | |
1843 | effort to clean up this mess, IBM documents the two types as being | |
1844 | separated by a semicolon, and a range type as not ending in a semicolon | |
1845 | (but this is not right for range types which are not array indexes, | |
1846 | @pxref{Subranges}). I think probably the best solution is to specify | |
1847 | that a semicolon ends a range type, and that the index type and element | |
1848 | type of an array are separated by a semicolon, but that if the index | |
1849 | type is a range type, the extra semicolon can be omitted. GDB (at least | |
1850 | through version 4.9) doesn't support any kind of index type other than a | |
1851 | range anyway; I'm not sure about dbx. | |
1852 | ||
1853 | It is well established, and widely used, that the type of the index, | |
1854 | unlike most types found in the stabs, is merely a type definition, not | |
1855 | type information (@pxref{String Field}) (that is, it need not start with | |
1856 | @samp{@var{type-number}=} if it is defining a new type). According to a | |
1857 | comment in GDB, this is also true of the type of the array elements; it | |
1858 | gives @samp{ar1;1;10;ar1;1;10;4} as a legitimate way to express a two | |
1859 | dimensional array. According to AIX documentation, the element type | |
1860 | must be type information. GDB accepts either. | |
1861 | ||
1862 | The type of the index is often a range type, expressed as the type | |
1863 | descriptor @samp{r} and some parameters. It defines the size of the | |
1864 | array. In the example below, the range @samp{r1;0;2;} defines an index | |
1865 | type which is a subrange of type 1 (integer), with a lower bound of 0 | |
1866 | and an upper bound of 2. This defines the valid range of subscripts of | |
1867 | a three-element C array. | |
1868 | ||
1869 | For example, the definition: | |
1870 | ||
1871 | @example | |
1872 | char char_vec[3] = @{'a','b','c'@}; | |
1873 | @end example | |
1874 | ||
1875 | @noindent | |
1876 | produces the output: | |
1877 | ||
1878 | @example | |
1879 | .stabs "char_vec:G19=ar1;0;2;2",32,0,0,0 | |
1880 | .global _char_vec | |
1881 | .align 4 | |
1882 | _char_vec: | |
1883 | .byte 97 | |
1884 | .byte 98 | |
1885 | .byte 99 | |
1886 | @end example | |
1887 | ||
1888 | If an array is @dfn{packed}, the elements are spaced more | |
1889 | closely than normal, saving memory at the expense of speed. For | |
1890 | example, an array of 3-byte objects might, if unpacked, have each | |
1891 | element aligned on a 4-byte boundary, but if packed, have no padding. | |
1892 | One way to specify that something is packed is with type attributes | |
1893 | (@pxref{String Field}). In the case of arrays, another is to use the | |
1894 | @samp{P} type descriptor instead of @samp{a}. Other than specifying a | |
1895 | packed array, @samp{P} is identical to @samp{a}. | |
1896 | ||
1897 | @c FIXME-what is it? A pointer? | |
1898 | An open array is represented by the @samp{A} type descriptor followed by | |
1899 | type information specifying the type of the array elements. | |
1900 | ||
1901 | @c FIXME: what is the format of this type? A pointer to a vector of pointers? | |
1902 | An N-dimensional dynamic array is represented by | |
1903 | ||
1904 | @example | |
1905 | D @var{dimensions} ; @var{type-information} | |
1906 | @end example | |
1907 | ||
1908 | @c Does dimensions really have this meaning? The AIX documentation | |
1909 | @c doesn't say. | |
1910 | @var{dimensions} is the number of dimensions; @var{type-information} | |
1911 | specifies the type of the array elements. | |
1912 | ||
1913 | @c FIXME: what is the format of this type? A pointer to some offsets in | |
1914 | @c another array? | |
1915 | A subarray of an N-dimensional array is represented by | |
1916 | ||
1917 | @example | |
1918 | E @var{dimensions} ; @var{type-information} | |
1919 | @end example | |
1920 | ||
1921 | @c Does dimensions really have this meaning? The AIX documentation | |
1922 | @c doesn't say. | |
1923 | @var{dimensions} is the number of dimensions; @var{type-information} | |
1924 | specifies the type of the array elements. | |
1925 | ||
1926 | @node Strings | |
1927 | @section Strings | |
1928 | ||
1929 | Some languages, like C or the original Pascal, do not have string types, | |
1930 | they just have related things like arrays of characters. But most | |
1931 | Pascals and various other languages have string types, which are | |
1932 | indicated as follows: | |
1933 | ||
1934 | @table @code | |
1935 | @item n @var{type-information} ; @var{bytes} | |
1936 | @var{bytes} is the maximum length. I'm not sure what | |
1937 | @var{type-information} is; I suspect that it means that this is a string | |
1938 | of @var{type-information} (thus allowing a string of integers, a string | |
1939 | of wide characters, etc., as well as a string of characters). Not sure | |
1940 | what the format of this type is. This is an AIX feature. | |
1941 | ||
1942 | @item z @var{type-information} ; @var{bytes} | |
1943 | Just like @samp{n} except that this is a gstring, not an ordinary | |
1944 | string. I don't know the difference. | |
1945 | ||
1946 | @item N | |
1947 | Pascal Stringptr. What is this? This is an AIX feature. | |
1948 | @end table | |
1949 | ||
1950 | Languages, such as CHILL which have a string type which is basically | |
1951 | just an array of characters use the @samp{S} type attribute | |
1952 | (@pxref{String Field}). | |
1953 | ||
1954 | @node Enumerations | |
1955 | @section Enumerations | |
1956 | ||
1957 | Enumerations are defined with the @samp{e} type descriptor. | |
1958 | ||
1959 | @c FIXME: Where does this information properly go? Perhaps it is | |
1960 | @c redundant with something we already explain. | |
1961 | The source line below declares an enumeration type at file scope. | |
1962 | The type definition is located after the @code{N_RBRAC} that marks the end of | |
1963 | the previous procedure's block scope, and before the @code{N_FUN} that marks | |
1964 | the beginning of the next procedure's block scope. Therefore it does not | |
1965 | describe a block local symbol, but a file local one. | |
1966 | ||
1967 | The source line: | |
1968 | ||
1969 | @example | |
1970 | enum e_places @{first,second=3,last@}; | |
1971 | @end example | |
1972 | ||
1973 | @noindent | |
1974 | generates the following stab: | |
1975 | ||
1976 | @example | |
1977 | .stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0 | |
1978 | @end example | |
1979 | ||
1980 | The symbol descriptor (@samp{T}) says that the stab describes a | |
1981 | structure, enumeration, or union tag. The type descriptor @samp{e}, | |
1982 | following the @samp{22=} of the type definition narrows it down to an | |
1983 | enumeration type. Following the @samp{e} is a list of the elements of | |
1984 | the enumeration. The format is @samp{@var{name}:@var{value},}. The | |
1985 | list of elements ends with @samp{;}. The fact that @var{value} is | |
1986 | specified as an integer can cause problems if the value is large. GCC | |
1987 | 2.5.2 tries to output it in octal in that case with a leading zero, | |
1988 | which is probably a good thing, although GDB 4.11 supports octal only in | |
1989 | cases where decimal is perfectly good. Negative decimal values are | |
1990 | supported by both GDB and dbx. | |
1991 | ||
1992 | There is no standard way to specify the size of an enumeration type; it | |
1993 | is determined by the architecture (normally all enumerations types are | |
1994 | 32 bits). Type attributes can be used to specify an enumeration type of | |
1995 | another size for debuggers which support them; see @ref{String Field}. | |
1996 | ||
1997 | Enumeration types are unusual in that they define symbols for the | |
1998 | enumeration values (@code{first}, @code{second}, and @code{third} in the | |
1999 | above example), and even though these symbols are visible in the file as | |
2000 | a whole (rather than being in a more local namespace like structure | |
2001 | member names), they are defined in the type definition for the | |
2002 | enumeration type rather than each having their own symbol. In order to | |
2003 | be fast, GDB will only get symbols from such types (in its initial scan | |
2004 | of the stabs) if the type is the first thing defined after a @samp{T} or | |
2005 | @samp{t} symbol descriptor (the above example fulfills this | |
2006 | requirement). If the type does not have a name, the compiler should | |
2007 | emit it in a nameless stab (@pxref{String Field}); GCC does this. | |
2008 | ||
2009 | @node Structures | |
2010 | @section Structures | |
2011 | ||
2012 | The encoding of structures in stabs can be shown with an example. | |
2013 | ||
2014 | The following source code declares a structure tag and defines an | |
2015 | instance of the structure in global scope. Then a @code{typedef} equates the | |
bd79f757 | 2016 | structure tag with a new type. Separate stabs are generated for the |
c906108c | 2017 | structure tag, the structure @code{typedef}, and the structure instance. The |
bd79f757 | 2018 | stabs for the tag and the @code{typedef} are emitted when the definitions are |
c906108c SS |
2019 | encountered. Since the structure elements are not initialized, the |
2020 | stab and code for the structure variable itself is located at the end | |
2021 | of the program in the bss section. | |
2022 | ||
2023 | @example | |
2024 | struct s_tag @{ | |
2025 | int s_int; | |
2026 | float s_float; | |
2027 | char s_char_vec[8]; | |
2028 | struct s_tag* s_next; | |
2029 | @} g_an_s; | |
2030 | ||
2031 | typedef struct s_tag s_typedef; | |
2032 | @end example | |
2033 | ||
2034 | The structure tag has an @code{N_LSYM} stab type because, like the | |
2035 | enumeration, the symbol has file scope. Like the enumeration, the | |
2036 | symbol descriptor is @samp{T}, for enumeration, structure, or tag type. | |
2037 | The type descriptor @samp{s} following the @samp{16=} of the type | |
2038 | definition narrows the symbol type to structure. | |
2039 | ||
2040 | Following the @samp{s} type descriptor is the number of bytes the | |
2041 | structure occupies, followed by a description of each structure element. | |
2042 | The structure element descriptions are of the form @var{name:type, bit | |
2043 | offset from the start of the struct, number of bits in the element}. | |
2044 | ||
2045 | @c FIXME: phony line break. Can probably be fixed by using an example | |
2046 | @c with fewer fields. | |
2047 | @example | |
2048 | # @r{128 is N_LSYM} | |
2049 | .stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32; | |
2050 | s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0 | |
2051 | @end example | |
2052 | ||
2053 | In this example, the first two structure elements are previously defined | |
2054 | types. For these, the type following the @samp{@var{name}:} part of the | |
2055 | element description is a simple type reference. The other two structure | |
2056 | elements are new types. In this case there is a type definition | |
2057 | embedded after the @samp{@var{name}:}. The type definition for the | |
bd79f757 | 2058 | array element looks just like a type definition for a stand-alone array. |
c906108c SS |
2059 | The @code{s_next} field is a pointer to the same kind of structure that |
2060 | the field is an element of. So the definition of structure type 16 | |
2061 | contains a type definition for an element which is a pointer to type 16. | |
2062 | ||
2063 | If a field is a static member (this is a C++ feature in which a single | |
2064 | variable appears to be a field of every structure of a given type) it | |
2065 | still starts out with the field name, a colon, and the type, but then | |
2066 | instead of a comma, bit position, comma, and bit size, there is a colon | |
2067 | followed by the name of the variable which each such field refers to. | |
2068 | ||
2069 | If the structure has methods (a C++ feature), they follow the non-method | |
2070 | fields; see @ref{Cplusplus}. | |
2071 | ||
2072 | @node Typedefs | |
2073 | @section Giving a Type a Name | |
2074 | ||
2075 | @findex N_LSYM, for types | |
2076 | @findex C_DECL, for types | |
2077 | To give a type a name, use the @samp{t} symbol descriptor. The type | |
2078 | is specified by the type information (@pxref{String Field}) for the stab. | |
2079 | For example, | |
2080 | ||
2081 | @example | |
2082 | .stabs "s_typedef:t16",128,0,0,0 # @r{128 is N_LSYM} | |
2083 | @end example | |
2084 | ||
2085 | specifies that @code{s_typedef} refers to type number 16. Such stabs | |
2086 | have symbol type @code{N_LSYM} (or @code{C_DECL} for XCOFF). (The Sun | |
2087 | documentation mentions using @code{N_GSYM} in some cases). | |
2088 | ||
2089 | If you are specifying the tag name for a structure, union, or | |
2090 | enumeration, use the @samp{T} symbol descriptor instead. I believe C is | |
2091 | the only language with this feature. | |
2092 | ||
2093 | If the type is an opaque type (I believe this is a Modula-2 feature), | |
2094 | AIX provides a type descriptor to specify it. The type descriptor is | |
2095 | @samp{o} and is followed by a name. I don't know what the name | |
2096 | means---is it always the same as the name of the type, or is this type | |
2097 | descriptor used with a nameless stab (@pxref{String Field})? There | |
2098 | optionally follows a comma followed by type information which defines | |
2099 | the type of this type. If omitted, a semicolon is used in place of the | |
2100 | comma and the type information, and the type is much like a generic | |
2101 | pointer type---it has a known size but little else about it is | |
2102 | specified. | |
2103 | ||
2104 | @node Unions | |
2105 | @section Unions | |
2106 | ||
2107 | @example | |
2108 | union u_tag @{ | |
2109 | int u_int; | |
2110 | float u_float; | |
2111 | char* u_char; | |
2112 | @} an_u; | |
2113 | @end example | |
2114 | ||
2115 | This code generates a stab for a union tag and a stab for a union | |
2116 | variable. Both use the @code{N_LSYM} stab type. If a union variable is | |
2117 | scoped locally to the procedure in which it is defined, its stab is | |
2118 | located immediately preceding the @code{N_LBRAC} for the procedure's block | |
2119 | start. | |
2120 | ||
2121 | The stab for the union tag, however, is located preceding the code for | |
2122 | the procedure in which it is defined. The stab type is @code{N_LSYM}. This | |
2123 | would seem to imply that the union type is file scope, like the struct | |
2124 | type @code{s_tag}. This is not true. The contents and position of the stab | |
bd79f757 | 2125 | for @code{u_type} do not convey any information about its procedure local |
c906108c SS |
2126 | scope. |
2127 | ||
2128 | @c FIXME: phony line break. Can probably be fixed by using an example | |
2129 | @c with fewer fields. | |
2130 | @smallexample | |
2131 | # @r{128 is N_LSYM} | |
2132 | .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;", | |
2133 | 128,0,0,0 | |
2134 | @end smallexample | |
2135 | ||
2136 | The symbol descriptor @samp{T}, following the @samp{name:} means that | |
2137 | the stab describes an enumeration, structure, or union tag. The type | |
2138 | descriptor @samp{u}, following the @samp{23=} of the type definition, | |
2139 | narrows it down to a union type definition. Following the @samp{u} is | |
2140 | the number of bytes in the union. After that is a list of union element | |
2141 | descriptions. Their format is @var{name:type, bit offset into the | |
2142 | union, number of bytes for the element;}. | |
2143 | ||
2144 | The stab for the union variable is: | |
2145 | ||
2146 | @example | |
2147 | .stabs "an_u:23",128,0,0,-20 # @r{128 is N_LSYM} | |
2148 | @end example | |
2149 | ||
2150 | @samp{-20} specifies where the variable is stored (@pxref{Stack | |
2151 | Variables}). | |
2152 | ||
2153 | @node Function Types | |
2154 | @section Function Types | |
2155 | ||
2156 | Various types can be defined for function variables. These types are | |
2157 | not used in defining functions (@pxref{Procedures}); they are used for | |
2158 | things like pointers to functions. | |
2159 | ||
2160 | The simple, traditional, type is type descriptor @samp{f} is followed by | |
2161 | type information for the return type of the function, followed by a | |
2162 | semicolon. | |
2163 | ||
2164 | This does not deal with functions for which the number and types of the | |
2165 | parameters are part of the type, as in Modula-2 or ANSI C. AIX provides | |
2166 | extensions to specify these, using the @samp{f}, @samp{F}, @samp{p}, and | |
2167 | @samp{R} type descriptors. | |
2168 | ||
2169 | First comes the type descriptor. If it is @samp{f} or @samp{F}, this | |
2170 | type involves a function rather than a procedure, and the type | |
2171 | information for the return type of the function follows, followed by a | |
2172 | comma. Then comes the number of parameters to the function and a | |
2173 | semicolon. Then, for each parameter, there is the name of the parameter | |
2174 | followed by a colon (this is only present for type descriptors @samp{R} | |
2175 | and @samp{F} which represent Pascal function or procedure parameters), | |
2176 | type information for the parameter, a comma, 0 if passed by reference or | |
2177 | 1 if passed by value, and a semicolon. The type definition ends with a | |
2178 | semicolon. | |
2179 | ||
2180 | For example, this variable definition: | |
2181 | ||
2182 | @example | |
2183 | int (*g_pf)(); | |
2184 | @end example | |
2185 | ||
2186 | @noindent | |
2187 | generates the following code: | |
2188 | ||
2189 | @example | |
2190 | .stabs "g_pf:G24=*25=f1",32,0,0,0 | |
2191 | .common _g_pf,4,"bss" | |
2192 | @end example | |
2193 | ||
2194 | The variable defines a new type, 24, which is a pointer to another new | |
2195 | type, 25, which is a function returning @code{int}. | |
2196 | ||
2197 | @node Symbol Tables | |
2198 | @chapter Symbol Information in Symbol Tables | |
2199 | ||
2200 | This chapter describes the format of symbol table entries | |
2201 | and how stab assembler directives map to them. It also describes the | |
2202 | transformations that the assembler and linker make on data from stabs. | |
2203 | ||
2204 | @menu | |
2205 | * Symbol Table Format:: | |
2206 | * Transformations On Symbol Tables:: | |
2207 | @end menu | |
2208 | ||
2209 | @node Symbol Table Format | |
2210 | @section Symbol Table Format | |
2211 | ||
2212 | Each time the assembler encounters a stab directive, it puts | |
2213 | each field of the stab into a corresponding field in a symbol table | |
2214 | entry of its output file. If the stab contains a string field, the | |
2215 | symbol table entry for that stab points to a string table entry | |
2216 | containing the string data from the stab. Assembler labels become | |
2217 | relocatable addresses. Symbol table entries in a.out have the format: | |
2218 | ||
2219 | @c FIXME: should refer to external, not internal. | |
2220 | @example | |
2221 | struct internal_nlist @{ | |
2222 | unsigned long n_strx; /* index into string table of name */ | |
2223 | unsigned char n_type; /* type of symbol */ | |
2224 | unsigned char n_other; /* misc info (usually empty) */ | |
2225 | unsigned short n_desc; /* description field */ | |
2226 | bfd_vma n_value; /* value of symbol */ | |
2227 | @}; | |
2228 | @end example | |
2229 | ||
2230 | If the stab has a string, the @code{n_strx} field holds the offset in | |
2231 | bytes of the string within the string table. The string is terminated | |
2232 | by a NUL character. If the stab lacks a string (for example, it was | |
2233 | produced by a @code{.stabn} or @code{.stabd} directive), the | |
2234 | @code{n_strx} field is zero. | |
2235 | ||
2236 | Symbol table entries with @code{n_type} field values greater than 0x1f | |
2237 | originated as stabs generated by the compiler (with one random | |
2238 | exception). The other entries were placed in the symbol table of the | |
2239 | executable by the assembler or the linker. | |
2240 | ||
2241 | @node Transformations On Symbol Tables | |
2242 | @section Transformations on Symbol Tables | |
2243 | ||
2244 | The linker concatenates object files and does fixups of externally | |
2245 | defined symbols. | |
2246 | ||
2247 | You can see the transformations made on stab data by the assembler and | |
2248 | linker by examining the symbol table after each pass of the build. To | |
2249 | do this, use @samp{nm -ap}, which dumps the symbol table, including | |
2250 | debugging information, unsorted. For stab entries the columns are: | |
2251 | @var{value}, @var{other}, @var{desc}, @var{type}, @var{string}. For | |
2252 | assembler and linker symbols, the columns are: @var{value}, @var{type}, | |
2253 | @var{string}. | |
2254 | ||
2255 | The low 5 bits of the stab type tell the linker how to relocate the | |
2256 | value of the stab. Thus for stab types like @code{N_RSYM} and | |
2257 | @code{N_LSYM}, where the value is an offset or a register number, the | |
2258 | low 5 bits are @code{N_ABS}, which tells the linker not to relocate the | |
2259 | value. | |
2260 | ||
2261 | Where the value of a stab contains an assembly language label, | |
2262 | it is transformed by each build step. The assembler turns it into a | |
2263 | relocatable address and the linker turns it into an absolute address. | |
2264 | ||
2265 | @menu | |
2266 | * Transformations On Static Variables:: | |
2267 | * Transformations On Global Variables:: | |
2268 | * Stab Section Transformations:: For some object file formats, | |
2269 | things are a bit different. | |
2270 | @end menu | |
2271 | ||
2272 | @node Transformations On Static Variables | |
2273 | @subsection Transformations on Static Variables | |
2274 | ||
2275 | This source line defines a static variable at file scope: | |
2276 | ||
2277 | @example | |
2278 | static int s_g_repeat | |
2279 | @end example | |
2280 | ||
2281 | @noindent | |
2282 | The following stab describes the symbol: | |
2283 | ||
2284 | @example | |
2285 | .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat | |
2286 | @end example | |
2287 | ||
2288 | @noindent | |
2289 | The assembler transforms the stab into this symbol table entry in the | |
2290 | @file{.o} file. The location is expressed as a data segment offset. | |
2291 | ||
2292 | @example | |
2293 | 00000084 - 00 0000 STSYM s_g_repeat:S1 | |
2294 | @end example | |
2295 | ||
2296 | @noindent | |
2297 | In the symbol table entry from the executable, the linker has made the | |
2298 | relocatable address absolute. | |
2299 | ||
2300 | @example | |
2301 | 0000e00c - 00 0000 STSYM s_g_repeat:S1 | |
2302 | @end example | |
2303 | ||
2304 | @node Transformations On Global Variables | |
2305 | @subsection Transformations on Global Variables | |
2306 | ||
2307 | Stabs for global variables do not contain location information. In | |
2308 | this case, the debugger finds location information in the assembler or | |
2309 | linker symbol table entry describing the variable. The source line: | |
2310 | ||
2311 | @example | |
2312 | char g_foo = 'c'; | |
2313 | @end example | |
2314 | ||
2315 | @noindent | |
2316 | generates the stab: | |
2317 | ||
2318 | @example | |
2319 | .stabs "g_foo:G2",32,0,0,0 | |
2320 | @end example | |
2321 | ||
2322 | The variable is represented by two symbol table entries in the object | |
2323 | file (see below). The first one originated as a stab. The second one | |
2324 | is an external symbol. The upper case @samp{D} signifies that the | |
2325 | @code{n_type} field of the symbol table contains 7, @code{N_DATA} with | |
2326 | local linkage. The stab's value is zero since the value is not used for | |
2327 | @code{N_GSYM} stabs. The value of the linker symbol is the relocatable | |
2328 | address corresponding to the variable. | |
2329 | ||
2330 | @example | |
2331 | 00000000 - 00 0000 GSYM g_foo:G2 | |
2332 | 00000080 D _g_foo | |
2333 | @end example | |
2334 | ||
2335 | @noindent | |
2336 | These entries as transformed by the linker. The linker symbol table | |
2337 | entry now holds an absolute address: | |
2338 | ||
2339 | @example | |
2340 | 00000000 - 00 0000 GSYM g_foo:G2 | |
2341 | @dots{} | |
2342 | 0000e008 D _g_foo | |
2343 | @end example | |
2344 | ||
2345 | @node Stab Section Transformations | |
2346 | @subsection Transformations of Stabs in separate sections | |
2347 | ||
2348 | For object file formats using stabs in separate sections (@pxref{Stab | |
2349 | Sections}), use @code{objdump --stabs} instead of @code{nm} to show the | |
2350 | stabs in an object or executable file. @code{objdump} is a GNU utility; | |
2351 | Sun does not provide any equivalent. | |
2352 | ||
2353 | The following example is for a stab whose value is an address is | |
2354 | relative to the compilation unit (@pxref{ELF Linker Relocation}). For | |
2355 | example, if the source line | |
2356 | ||
2357 | @example | |
2358 | static int ld = 5; | |
2359 | @end example | |
2360 | ||
2361 | appears within a function, then the assembly language output from the | |
2362 | compiler contains: | |
2363 | ||
2364 | @example | |
2365 | .Ddata.data: | |
2366 | @dots{} | |
2367 | .stabs "ld:V(0,3)",0x26,0,4,.L18-Ddata.data # @r{0x26 is N_STSYM} | |
2368 | @dots{} | |
2369 | .L18: | |
2370 | .align 4 | |
2371 | .word 0x5 | |
2372 | @end example | |
2373 | ||
2374 | Because the value is formed by subtracting one symbol from another, the | |
2375 | value is absolute, not relocatable, and so the object file contains | |
2376 | ||
2377 | @example | |
2378 | Symnum n_type n_othr n_desc n_value n_strx String | |
2379 | 31 STSYM 0 4 00000004 680 ld:V(0,3) | |
2380 | @end example | |
2381 | ||
2382 | without any relocations, and the executable file also contains | |
2383 | ||
2384 | @example | |
2385 | Symnum n_type n_othr n_desc n_value n_strx String | |
2386 | 31 STSYM 0 4 00000004 680 ld:V(0,3) | |
2387 | @end example | |
2388 | ||
2389 | @node Cplusplus | |
2390 | @chapter GNU C++ Stabs | |
2391 | ||
2392 | @menu | |
2393 | * Class Names:: C++ class names are both tags and typedefs. | |
2394 | * Nested Symbols:: C++ symbol names can be within other types. | |
2395 | * Basic Cplusplus Types:: | |
2396 | * Simple Classes:: | |
2397 | * Class Instance:: | |
2398 | * Methods:: Method definition | |
2399 | * Method Type Descriptor:: The @samp{#} type descriptor | |
2400 | * Member Type Descriptor:: The @samp{@@} type descriptor | |
2401 | * Protections:: | |
2402 | * Method Modifiers:: | |
2403 | * Virtual Methods:: | |
bd79f757 | 2404 | * Inheritance:: |
c906108c SS |
2405 | * Virtual Base Classes:: |
2406 | * Static Members:: | |
2407 | @end menu | |
2408 | ||
2409 | @node Class Names | |
2410 | @section C++ Class Names | |
2411 | ||
2412 | In C++, a class name which is declared with @code{class}, @code{struct}, | |
2413 | or @code{union}, is not only a tag, as in C, but also a type name. Thus | |
2414 | there should be stabs with both @samp{t} and @samp{T} symbol descriptors | |
2415 | (@pxref{Typedefs}). | |
2416 | ||
2417 | To save space, there is a special abbreviation for this case. If the | |
2418 | @samp{T} symbol descriptor is followed by @samp{t}, then the stab | |
2419 | defines both a type name and a tag. | |
2420 | ||
2421 | For example, the C++ code | |
2422 | ||
2423 | @example | |
2424 | struct foo @{int x;@}; | |
2425 | @end example | |
2426 | ||
2427 | can be represented as either | |
2428 | ||
2429 | @example | |
2430 | .stabs "foo:T19=s4x:1,0,32;;",128,0,0,0 # @r{128 is N_LSYM} | |
2431 | .stabs "foo:t19",128,0,0,0 | |
2432 | @end example | |
2433 | ||
2434 | or | |
2435 | ||
2436 | @example | |
2437 | .stabs "foo:Tt19=s4x:1,0,32;;",128,0,0,0 | |
2438 | @end example | |
2439 | ||
2440 | @node Nested Symbols | |
2441 | @section Defining a Symbol Within Another Type | |
2442 | ||
2443 | In C++, a symbol (such as a type name) can be defined within another type. | |
2444 | @c FIXME: Needs example. | |
2445 | ||
2446 | In stabs, this is sometimes represented by making the name of a symbol | |
2447 | which contains @samp{::}. Such a pair of colons does not end the name | |
2448 | of the symbol, the way a single colon would (@pxref{String Field}). I'm | |
2449 | not sure how consistently used or well thought out this mechanism is. | |
2450 | So that a pair of colons in this position always has this meaning, | |
2451 | @samp{:} cannot be used as a symbol descriptor. | |
2452 | ||
2453 | For example, if the string for a stab is @samp{foo::bar::baz:t5=*6}, | |
2454 | then @code{foo::bar::baz} is the name of the symbol, @samp{t} is the | |
2455 | symbol descriptor, and @samp{5=*6} is the type information. | |
2456 | ||
2457 | @node Basic Cplusplus Types | |
2458 | @section Basic Types For C++ | |
2459 | ||
2460 | << the examples that follow are based on a01.C >> | |
2461 | ||
2462 | ||
2463 | C++ adds two more builtin types to the set defined for C. These are | |
2464 | the unknown type and the vtable record type. The unknown type, type | |
2465 | 16, is defined in terms of itself like the void type. | |
2466 | ||
2467 | The vtable record type, type 17, is defined as a structure type and | |
2468 | then as a structure tag. The structure has four fields: delta, index, | |
2469 | pfn, and delta2. pfn is the function pointer. | |
2470 | ||
2471 | << In boilerplate $vtbl_ptr_type, what are the fields delta, | |
2472 | index, and delta2 used for? >> | |
2473 | ||
2474 | This basic type is present in all C++ programs even if there are no | |
2475 | virtual methods defined. | |
2476 | ||
2477 | @display | |
2478 | .stabs "struct_name:sym_desc(type)type_def(17)=type_desc(struct)struct_bytes(8) | |
2479 | elem_name(delta):type_ref(short int),bit_offset(0),field_bits(16); | |
2480 | elem_name(index):type_ref(short int),bit_offset(16),field_bits(16); | |
2481 | elem_name(pfn):type_def(18)=type_desc(ptr to)type_ref(void), | |
2482 | bit_offset(32),field_bits(32); | |
2483 | elem_name(delta2):type_def(short int);bit_offset(32),field_bits(16);;" | |
2484 | N_LSYM, NIL, NIL | |
2485 | @end display | |
2486 | ||
2487 | @smallexample | |
2488 | .stabs "$vtbl_ptr_type:t17=s8 | |
2489 | delta:6,0,16;index:6,16,16;pfn:18=*15,32,32;delta2:6,32,16;;" | |
2490 | ,128,0,0,0 | |
2491 | @end smallexample | |
2492 | ||
2493 | @display | |
2494 | .stabs "name:sym_dec(struct tag)type_ref($vtbl_ptr_type)",N_LSYM,NIL,NIL,NIL | |
2495 | @end display | |
2496 | ||
2497 | @example | |
2498 | .stabs "$vtbl_ptr_type:T17",128,0,0,0 | |
2499 | @end example | |
2500 | ||
2501 | @node Simple Classes | |
2502 | @section Simple Class Definition | |
2503 | ||
2504 | The stabs describing C++ language features are an extension of the | |
2505 | stabs describing C. Stabs representing C++ class types elaborate | |
2506 | extensively on the stab format used to describe structure types in C. | |
2507 | Stabs representing class type variables look just like stabs | |
2508 | representing C language variables. | |
2509 | ||
2510 | Consider the following very simple class definition. | |
2511 | ||
2512 | @example | |
2513 | class baseA @{ | |
2514 | public: | |
2515 | int Adat; | |
2516 | int Ameth(int in, char other); | |
2517 | @}; | |
2518 | @end example | |
2519 | ||
2520 | The class @code{baseA} is represented by two stabs. The first stab describes | |
2521 | the class as a structure type. The second stab describes a structure | |
2522 | tag of the class type. Both stabs are of stab type @code{N_LSYM}. Since the | |
2523 | stab is not located between an @code{N_FUN} and an @code{N_LBRAC} stab this indicates | |
2524 | that the class is defined at file scope. If it were, then the @code{N_LSYM} | |
2525 | would signify a local variable. | |
2526 | ||
2527 | A stab describing a C++ class type is similar in format to a stab | |
2528 | describing a C struct, with each class member shown as a field in the | |
2529 | structure. The part of the struct format describing fields is | |
bd79f757 | 2530 | expanded to include extra information relevant to C++ class members. |
c906108c SS |
2531 | In addition, if the class has multiple base classes or virtual |
2532 | functions the struct format outside of the field parts is also | |
2533 | augmented. | |
2534 | ||
2535 | In this simple example the field part of the C++ class stab | |
2536 | representing member data looks just like the field part of a C struct | |
2537 | stab. The section on protections describes how its format is | |
2538 | sometimes extended for member data. | |
2539 | ||
2540 | The field part of a C++ class stab representing a member function | |
2541 | differs substantially from the field part of a C struct stab. It | |
2542 | still begins with @samp{name:} but then goes on to define a new type number | |
2543 | for the member function, describe its return type, its argument types, | |
2544 | its protection level, any qualifiers applied to the method definition, | |
2545 | and whether the method is virtual or not. If the method is virtual | |
2546 | then the method description goes on to give the vtable index of the | |
2547 | method, and the type number of the first base class defining the | |
2548 | method. | |
2549 | ||
2550 | When the field name is a method name it is followed by two colons rather | |
2551 | than one. This is followed by a new type definition for the method. | |
2552 | This is a number followed by an equal sign and the type of the method. | |
2553 | Normally this will be a type declared using the @samp{#} type | |
2554 | descriptor; see @ref{Method Type Descriptor}; static member functions | |
2555 | are declared using the @samp{f} type descriptor instead; see | |
2556 | @ref{Function Types}. | |
2557 | ||
2558 | The format of an overloaded operator method name differs from that of | |
2559 | other methods. It is @samp{op$::@var{operator-name}.} where | |
2560 | @var{operator-name} is the operator name such as @samp{+} or @samp{+=}. | |
2561 | The name ends with a period, and any characters except the period can | |
2562 | occur in the @var{operator-name} string. | |
2563 | ||
2564 | The next part of the method description represents the arguments to the | |
bd79f757 | 2565 | method, preceded by a colon and ending with a semi-colon. The types of |
c906108c SS |
2566 | the arguments are expressed in the same way argument types are expressed |
2567 | in C++ name mangling. In this example an @code{int} and a @code{char} | |
2568 | map to @samp{ic}. | |
2569 | ||
2570 | This is followed by a number, a letter, and an asterisk or period, | |
2571 | followed by another semicolon. The number indicates the protections | |
2572 | that apply to the member function. Here the 2 means public. The | |
2573 | letter encodes any qualifier applied to the method definition. In | |
2574 | this case, @samp{A} means that it is a normal function definition. The dot | |
2575 | shows that the method is not virtual. The sections that follow | |
2576 | elaborate further on these fields and describe the additional | |
2577 | information present for virtual methods. | |
2578 | ||
2579 | ||
2580 | @display | |
2581 | .stabs "class_name:sym_desc(type)type_def(20)=type_desc(struct)struct_bytes(4) | |
2582 | field_name(Adat):type(int),bit_offset(0),field_bits(32); | |
2583 | ||
2584 | method_name(Ameth)::type_def(21)=type_desc(method)return_type(int); | |
2585 | :arg_types(int char); | |
2586 | protection(public)qualifier(normal)virtual(no);;" | |
2587 | N_LSYM,NIL,NIL,NIL | |
2588 | @end display | |
2589 | ||
2590 | @smallexample | |
2591 | .stabs "baseA:t20=s4Adat:1,0,32;Ameth::21=##1;:ic;2A.;;",128,0,0,0 | |
2592 | ||
2593 | .stabs "class_name:sym_desc(struct tag)",N_LSYM,NIL,NIL,NIL | |
2594 | ||
2595 | .stabs "baseA:T20",128,0,0,0 | |
2596 | @end smallexample | |
2597 | ||
2598 | @node Class Instance | |
2599 | @section Class Instance | |
2600 | ||
2601 | As shown above, describing even a simple C++ class definition is | |
2602 | accomplished by massively extending the stab format used in C to | |
2603 | describe structure types. However, once the class is defined, C stabs | |
2604 | with no modifications can be used to describe class instances. The | |
2605 | following source: | |
2606 | ||
2607 | @example | |
2608 | main () @{ | |
2609 | baseA AbaseA; | |
2610 | @} | |
2611 | @end example | |
2612 | ||
2613 | @noindent | |
2614 | yields the following stab describing the class instance. It looks no | |
2615 | different from a standard C stab describing a local variable. | |
2616 | ||
2617 | @display | |
2618 | .stabs "name:type_ref(baseA)", N_LSYM, NIL, NIL, frame_ptr_offset | |
2619 | @end display | |
2620 | ||
2621 | @example | |
2622 | .stabs "AbaseA:20",128,0,0,-20 | |
2623 | @end example | |
2624 | ||
2625 | @node Methods | |
2626 | @section Method Definition | |
2627 | ||
2628 | The class definition shown above declares Ameth. The C++ source below | |
2629 | defines Ameth: | |
2630 | ||
2631 | @example | |
2632 | int | |
2633 | baseA::Ameth(int in, char other) | |
2634 | @{ | |
2635 | return in; | |
2636 | @}; | |
2637 | @end example | |
2638 | ||
2639 | ||
2640 | This method definition yields three stabs following the code of the | |
2641 | method. One stab describes the method itself and following two describe | |
2642 | its parameters. Although there is only one formal argument all methods | |
2643 | have an implicit argument which is the @code{this} pointer. The @code{this} | |
2644 | pointer is a pointer to the object on which the method was called. Note | |
2645 | that the method name is mangled to encode the class name and argument | |
2646 | types. Name mangling is described in the @sc{arm} (@cite{The Annotated | |
2647 | C++ Reference Manual}, by Ellis and Stroustrup, @sc{isbn} | |
2648 | 0-201-51459-1); @file{gpcompare.texi} in Cygnus GCC distributions | |
2649 | describes the differences between GNU mangling and @sc{arm} | |
2650 | mangling. | |
2651 | @c FIXME: Use @xref, especially if this is generally installed in the | |
2652 | @c info tree. | |
2653 | @c FIXME: This information should be in a net release, either of GCC or | |
2654 | @c GDB. But gpcompare.texi doesn't seem to be in the FSF GCC. | |
2655 | ||
2656 | @example | |
bd79f757 | 2657 | .stabs "name:symbol_descriptor(global function)return_type(int)", |
c906108c SS |
2658 | N_FUN, NIL, NIL, code_addr_of_method_start |
2659 | ||
2660 | .stabs "Ameth__5baseAic:F1",36,0,0,_Ameth__5baseAic | |
2661 | @end example | |
2662 | ||
2663 | Here is the stab for the @code{this} pointer implicit argument. The | |
2664 | name of the @code{this} pointer is always @code{this}. Type 19, the | |
2665 | @code{this} pointer is defined as a pointer to type 20, @code{baseA}, | |
bd79f757 ND |
2666 | but a stab defining @code{baseA} has not yet been emitted. Since the |
2667 | compiler knows it will be emitted shortly, here it just outputs a cross | |
c906108c SS |
2668 | reference to the undefined symbol, by prefixing the symbol name with |
2669 | @samp{xs}. | |
2670 | ||
2671 | @example | |
2672 | .stabs "name:sym_desc(register param)type_def(19)= | |
2673 | type_desc(ptr to)type_ref(baseA)= | |
2674 | type_desc(cross-reference to)baseA:",N_RSYM,NIL,NIL,register_number | |
2675 | ||
2676 | .stabs "this:P19=*20=xsbaseA:",64,0,0,8 | |
2677 | @end example | |
2678 | ||
2679 | The stab for the explicit integer argument looks just like a parameter | |
2680 | to a C function. The last field of the stab is the offset from the | |
2681 | argument pointer, which in most systems is the same as the frame | |
2682 | pointer. | |
2683 | ||
2684 | @example | |
2685 | .stabs "name:sym_desc(value parameter)type_ref(int)", | |
2686 | N_PSYM,NIL,NIL,offset_from_arg_ptr | |
2687 | ||
2688 | .stabs "in:p1",160,0,0,72 | |
2689 | @end example | |
2690 | ||
2691 | << The examples that follow are based on A1.C >> | |
2692 | ||
2693 | @node Method Type Descriptor | |
2694 | @section The @samp{#} Type Descriptor | |
2695 | ||
2696 | This is used to describe a class method. This is a function which takes | |
2697 | an extra argument as its first argument, for the @code{this} pointer. | |
2698 | ||
2699 | If the @samp{#} is immediately followed by another @samp{#}, the second | |
2700 | one will be followed by the return type and a semicolon. The class and | |
2701 | argument types are not specified, and must be determined by demangling | |
2702 | the name of the method if it is available. | |
2703 | ||
2704 | Otherwise, the single @samp{#} is followed by the class type, a comma, | |
2705 | the return type, a comma, and zero or more parameter types separated by | |
2706 | commas. The list of arguments is terminated by a semicolon. In the | |
2707 | debugging output generated by gcc, a final argument type of @code{void} | |
2708 | indicates a method which does not take a variable number of arguments. | |
2709 | If the final argument type of @code{void} does not appear, the method | |
2710 | was declared with an ellipsis. | |
2711 | ||
2712 | Note that although such a type will normally be used to describe fields | |
2713 | in structures, unions, or classes, for at least some versions of the | |
2714 | compiler it can also be used in other contexts. | |
2715 | ||
2716 | @node Member Type Descriptor | |
2717 | @section The @samp{@@} Type Descriptor | |
2718 | ||
2719 | The @samp{@@} type descriptor is for a member (class and variable) type. | |
2720 | It is followed by type information for the offset basetype, a comma, and | |
2721 | type information for the type of the field being pointed to. (FIXME: | |
2722 | this is acknowledged to be gibberish. Can anyone say what really goes | |
2723 | here?). | |
2724 | ||
2725 | Note that there is a conflict between this and type attributes | |
2726 | (@pxref{String Field}); both use type descriptor @samp{@@}. | |
2727 | Fortunately, the @samp{@@} type descriptor used in this C++ sense always | |
2728 | will be followed by a digit, @samp{(}, or @samp{-}, and type attributes | |
2729 | never start with those things. | |
2730 | ||
2731 | @node Protections | |
2732 | @section Protections | |
2733 | ||
2734 | In the simple class definition shown above all member data and | |
bd79f757 ND |
2735 | functions were publicly accessible. The example that follows |
2736 | contrasts public, protected and privately accessible fields and shows | |
c906108c SS |
2737 | how these protections are encoded in C++ stabs. |
2738 | ||
2739 | If the character following the @samp{@var{field-name}:} part of the | |
2740 | string is @samp{/}, then the next character is the visibility. @samp{0} | |
2741 | means private, @samp{1} means protected, and @samp{2} means public. | |
2742 | Debuggers should ignore visibility characters they do not recognize, and | |
2743 | assume a reasonable default (such as public) (GDB 4.11 does not, but | |
2744 | this should be fixed in the next GDB release). If no visibility is | |
2745 | specified the field is public. The visibility @samp{9} means that the | |
2746 | field has been optimized out and is public (there is no way to specify | |
2747 | an optimized out field with a private or protected visibility). | |
2748 | Visibility @samp{9} is not supported by GDB 4.11; this should be fixed | |
2749 | in the next GDB release. | |
2750 | ||
2751 | The following C++ source: | |
2752 | ||
2753 | @example | |
2754 | class vis @{ | |
2755 | private: | |
2756 | int priv; | |
2757 | protected: | |
2758 | char prot; | |
2759 | public: | |
2760 | float pub; | |
2761 | @}; | |
2762 | @end example | |
2763 | ||
2764 | @noindent | |
2765 | generates the following stab: | |
2766 | ||
2767 | @example | |
2768 | # @r{128 is N_LSYM} | |
2769 | .stabs "vis:T19=s12priv:/01,0,32;prot:/12,32,8;pub:12,64,32;;",128,0,0,0 | |
2770 | @end example | |
2771 | ||
2772 | @samp{vis:T19=s12} indicates that type number 19 is a 12 byte structure | |
2773 | named @code{vis} The @code{priv} field has public visibility | |
2774 | (@samp{/0}), type int (@samp{1}), and offset and size @samp{,0,32;}. | |
2775 | The @code{prot} field has protected visibility (@samp{/1}), type char | |
2776 | (@samp{2}) and offset and size @samp{,32,8;}. The @code{pub} field has | |
2777 | type float (@samp{12}), and offset and size @samp{,64,32;}. | |
2778 | ||
bd79f757 | 2779 | Protections for member functions are signified by one digit embedded in |
c906108c SS |
2780 | the field part of the stab describing the method. The digit is 0 if |
2781 | private, 1 if protected and 2 if public. Consider the C++ class | |
2782 | definition below: | |
2783 | ||
2784 | @example | |
2785 | class all_methods @{ | |
2786 | private: | |
2787 | int priv_meth(int in)@{return in;@}; | |
2788 | protected: | |
2789 | char protMeth(char in)@{return in;@}; | |
2790 | public: | |
2791 | float pubMeth(float in)@{return in;@}; | |
2792 | @}; | |
2793 | @end example | |
2794 | ||
2795 | It generates the following stab. The digit in question is to the left | |
2796 | of an @samp{A} in each case. Notice also that in this case two symbol | |
2797 | descriptors apply to the class name struct tag and struct type. | |
2798 | ||
2799 | @display | |
2800 | .stabs "class_name:sym_desc(struct tag&type)type_def(21)= | |
2801 | sym_desc(struct)struct_bytes(1) | |
2802 | meth_name::type_def(22)=sym_desc(method)returning(int); | |
2803 | :args(int);protection(private)modifier(normal)virtual(no); | |
2804 | meth_name::type_def(23)=sym_desc(method)returning(char); | |
bd79f757 | 2805 | :args(char);protection(protected)modifier(normal)virtual(no); |
c906108c SS |
2806 | meth_name::type_def(24)=sym_desc(method)returning(float); |
2807 | :args(float);protection(public)modifier(normal)virtual(no);;", | |
2808 | N_LSYM,NIL,NIL,NIL | |
2809 | @end display | |
2810 | ||
2811 | @smallexample | |
2812 | .stabs "all_methods:Tt21=s1priv_meth::22=##1;:i;0A.;protMeth::23=##2;:c;1A.; | |
2813 | pubMeth::24=##12;:f;2A.;;",128,0,0,0 | |
2814 | @end smallexample | |
2815 | ||
2816 | @node Method Modifiers | |
2817 | @section Method Modifiers (@code{const}, @code{volatile}, @code{const volatile}) | |
2818 | ||
2819 | << based on a6.C >> | |
2820 | ||
2821 | In the class example described above all the methods have the normal | |
2822 | modifier. This method modifier information is located just after the | |
2823 | protection information for the method. This field has four possible | |
2824 | character values. Normal methods use @samp{A}, const methods use | |
2825 | @samp{B}, volatile methods use @samp{C}, and const volatile methods use | |
2826 | @samp{D}. Consider the class definition below: | |
2827 | ||
2828 | @example | |
2829 | class A @{ | |
2830 | public: | |
2831 | int ConstMeth (int arg) const @{ return arg; @}; | |
2832 | char VolatileMeth (char arg) volatile @{ return arg; @}; | |
2833 | float ConstVolMeth (float arg) const volatile @{return arg; @}; | |
2834 | @}; | |
2835 | @end example | |
2836 | ||
2837 | This class is described by the following stab: | |
2838 | ||
2839 | @display | |
2840 | .stabs "class(A):sym_desc(struct)type_def(20)=type_desc(struct)struct_bytes(1) | |
2841 | meth_name(ConstMeth)::type_def(21)sym_desc(method) | |
2842 | returning(int);:arg(int);protection(public)modifier(const)virtual(no); | |
2843 | meth_name(VolatileMeth)::type_def(22)=sym_desc(method) | |
2844 | returning(char);:arg(char);protection(public)modifier(volatile)virt(no) | |
2845 | meth_name(ConstVolMeth)::type_def(23)=sym_desc(method) | |
bd79f757 | 2846 | returning(float);:arg(float);protection(public)modifier(const volatile) |
c906108c SS |
2847 | virtual(no);;", @dots{} |
2848 | @end display | |
2849 | ||
2850 | @example | |
2851 | .stabs "A:T20=s1ConstMeth::21=##1;:i;2B.;VolatileMeth::22=##2;:c;2C.; | |
2852 | ConstVolMeth::23=##12;:f;2D.;;",128,0,0,0 | |
2853 | @end example | |
2854 | ||
2855 | @node Virtual Methods | |
2856 | @section Virtual Methods | |
2857 | ||
2858 | << The following examples are based on a4.C >> | |
2859 | ||
2860 | The presence of virtual methods in a class definition adds additional | |
2861 | data to the class description. The extra data is appended to the | |
2862 | description of the virtual method and to the end of the class | |
2863 | description. Consider the class definition below: | |
2864 | ||
2865 | @example | |
2866 | class A @{ | |
2867 | public: | |
2868 | int Adat; | |
2869 | virtual int A_virt (int arg) @{ return arg; @}; | |
2870 | @}; | |
2871 | @end example | |
2872 | ||
2873 | This results in the stab below describing class A. It defines a new | |
2874 | type (20) which is an 8 byte structure. The first field of the class | |
2875 | struct is @samp{Adat}, an integer, starting at structure offset 0 and | |
2876 | occupying 32 bits. | |
2877 | ||
2878 | The second field in the class struct is not explicitly defined by the | |
2879 | C++ class definition but is implied by the fact that the class | |
2880 | contains a virtual method. This field is the vtable pointer. The | |
2881 | name of the vtable pointer field starts with @samp{$vf} and continues with a | |
2882 | type reference to the class it is part of. In this example the type | |
2883 | reference for class A is 20 so the name of its vtable pointer field is | |
2884 | @samp{$vf20}, followed by the usual colon. | |
2885 | ||
2886 | Next there is a type definition for the vtable pointer type (21). | |
2887 | This is in turn defined as a pointer to another new type (22). | |
2888 | ||
2889 | Type 22 is the vtable itself, which is defined as an array, indexed by | |
2890 | a range of integers between 0 and 1, and whose elements are of type | |
2891 | 17. Type 17 was the vtable record type defined by the boilerplate C++ | |
2892 | type definitions, as shown earlier. | |
2893 | ||
2894 | The bit offset of the vtable pointer field is 32. The number of bits | |
2895 | in the field are not specified when the field is a vtable pointer. | |
2896 | ||
2897 | Next is the method definition for the virtual member function @code{A_virt}. | |
2898 | Its description starts out using the same format as the non-virtual | |
2899 | member functions described above, except instead of a dot after the | |
2900 | @samp{A} there is an asterisk, indicating that the function is virtual. | |
2901 | Since is is virtual some addition information is appended to the end | |
2902 | of the method description. | |
2903 | ||
2904 | The first number represents the vtable index of the method. This is a | |
2905 | 32 bit unsigned number with the high bit set, followed by a | |
2906 | semi-colon. | |
2907 | ||
2908 | The second number is a type reference to the first base class in the | |
bd79f757 | 2909 | inheritance hierarchy defining the virtual member function. In this |
c906108c SS |
2910 | case the class stab describes a base class so the virtual function is |
2911 | not overriding any other definition of the method. Therefore the | |
2912 | reference is to the type number of the class that the stab is | |
2913 | describing (20). | |
2914 | ||
2915 | This is followed by three semi-colons. One marks the end of the | |
2916 | current sub-section, one marks the end of the method field, and the | |
2917 | third marks the end of the struct definition. | |
2918 | ||
2919 | For classes containing virtual functions the very last section of the | |
2920 | string part of the stab holds a type reference to the first base | |
bd79f757 | 2921 | class. This is preceded by @samp{~%} and followed by a final semi-colon. |
c906108c SS |
2922 | |
2923 | @display | |
2924 | .stabs "class_name(A):type_def(20)=sym_desc(struct)struct_bytes(8) | |
2925 | field_name(Adat):type_ref(int),bit_offset(0),field_bits(32); | |
2926 | field_name(A virt func ptr):type_def(21)=type_desc(ptr to)type_def(22)= | |
2927 | sym_desc(array)index_type_ref(range of int from 0 to 1); | |
2928 | elem_type_ref(vtbl elem type), | |
2929 | bit_offset(32); | |
2930 | meth_name(A_virt)::typedef(23)=sym_desc(method)returning(int); | |
2931 | :arg_type(int),protection(public)normal(yes)virtual(yes) | |
2932 | vtable_index(1);class_first_defining(A);;;~%first_base(A);", | |
2933 | N_LSYM,NIL,NIL,NIL | |
2934 | @end display | |
2935 | ||
2936 | @c FIXME: bogus line break. | |
2937 | @example | |
2938 | .stabs "A:t20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32; | |
2939 | A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0 | |
2940 | @end example | |
2941 | ||
bd79f757 ND |
2942 | @node Inheritance |
2943 | @section Inheritance | |
c906108c SS |
2944 | |
2945 | Stabs describing C++ derived classes include additional sections that | |
bd79f757 | 2946 | describe the inheritance hierarchy of the class. A derived class stab |
c906108c | 2947 | also encodes the number of base classes. For each base class it tells |
bd79f757 | 2948 | if the base class is virtual or not, and if the inheritance is private |
c906108c SS |
2949 | or public. It also gives the offset into the object of the portion of |
2950 | the object corresponding to each base class. | |
2951 | ||
bd79f757 | 2952 | This additional information is embedded in the class stab following the |
c906108c SS |
2953 | number of bytes in the struct. First the number of base classes |
2954 | appears bracketed by an exclamation point and a comma. | |
2955 | ||
2956 | Then for each base type there repeats a series: a virtual character, a | |
bd79f757 | 2957 | visibility character, a number, a comma, another number, and a |
c906108c SS |
2958 | semi-colon. |
2959 | ||
2960 | The virtual character is @samp{1} if the base class is virtual and | |
2961 | @samp{0} if not. The visibility character is @samp{2} if the derivation | |
2962 | is public, @samp{1} if it is protected, and @samp{0} if it is private. | |
2963 | Debuggers should ignore virtual or visibility characters they do not | |
2964 | recognize, and assume a reasonable default (such as public and | |
2965 | non-virtual) (GDB 4.11 does not, but this should be fixed in the next | |
2966 | GDB release). | |
2967 | ||
2968 | The number following the virtual and visibility characters is the offset | |
2969 | from the start of the object to the part of the object pertaining to the | |
2970 | base class. | |
2971 | ||
2972 | After the comma, the second number is a type_descriptor for the base | |
2973 | type. Finally a semi-colon ends the series, which repeats for each | |
2974 | base class. | |
2975 | ||
2976 | The source below defines three base classes @code{A}, @code{B}, and | |
2977 | @code{C} and the derived class @code{D}. | |
2978 | ||
2979 | ||
2980 | @example | |
2981 | class A @{ | |
2982 | public: | |
2983 | int Adat; | |
2984 | virtual int A_virt (int arg) @{ return arg; @}; | |
2985 | @}; | |
2986 | ||
2987 | class B @{ | |
2988 | public: | |
2989 | int B_dat; | |
2990 | virtual int B_virt (int arg) @{return arg; @}; | |
2991 | @}; | |
2992 | ||
2993 | class C @{ | |
2994 | public: | |
2995 | int Cdat; | |
2996 | virtual int C_virt (int arg) @{return arg; @}; | |
2997 | @}; | |
2998 | ||
2999 | class D : A, virtual B, public C @{ | |
3000 | public: | |
3001 | int Ddat; | |
3002 | virtual int A_virt (int arg ) @{ return arg+1; @}; | |
3003 | virtual int B_virt (int arg) @{ return arg+2; @}; | |
3004 | virtual int C_virt (int arg) @{ return arg+3; @}; | |
3005 | virtual int D_virt (int arg) @{ return arg; @}; | |
3006 | @}; | |
3007 | @end example | |
3008 | ||
3009 | Class stabs similar to the ones described earlier are generated for | |
3010 | each base class. | |
3011 | ||
3012 | @c FIXME!!! the linebreaks in the following example probably make the | |
3013 | @c examples literally unusable, but I don't know any other way to get | |
3014 | @c them on the page. | |
3015 | @c One solution would be to put some of the type definitions into | |
3016 | @c separate stabs, even if that's not exactly what the compiler actually | |
3017 | @c emits. | |
3018 | @smallexample | |
3019 | .stabs "A:T20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32; | |
3020 | A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0 | |
3021 | ||
3022 | .stabs "B:Tt25=s8Bdat:1,0,32;$vf25:21,32;B_virt::26=##1; | |
3023 | :i;2A*-2147483647;25;;;~%25;",128,0,0,0 | |
3024 | ||
3025 | .stabs "C:Tt28=s8Cdat:1,0,32;$vf28:21,32;C_virt::29=##1; | |
3026 | :i;2A*-2147483647;28;;;~%28;",128,0,0,0 | |
3027 | @end smallexample | |
3028 | ||
3029 | In the stab describing derived class @code{D} below, the information about | |
3030 | the derivation of this class is encoded as follows. | |
3031 | ||
3032 | @display | |
3033 | .stabs "derived_class_name:symbol_descriptors(struct tag&type)= | |
3034 | type_descriptor(struct)struct_bytes(32)!num_bases(3), | |
bd79f757 | 3035 | base_virtual(no)inheritance_public(no)base_offset(0), |
c906108c | 3036 | base_class_type_ref(A); |
bd79f757 | 3037 | base_virtual(yes)inheritance_public(no)base_offset(NIL), |
c906108c | 3038 | base_class_type_ref(B); |
bd79f757 | 3039 | base_virtual(no)inheritance_public(yes)base_offset(64), |
c906108c SS |
3040 | base_class_type_ref(C); @dots{} |
3041 | @end display | |
3042 | ||
3043 | @c FIXME! fake linebreaks. | |
3044 | @smallexample | |
3045 | .stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat: | |
3046 | 1,160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt: | |
3047 | :32:i;2A*-2147483647;25;;C_virt::32:i;2A*-2147483647; | |
3048 | 28;;D_virt::32:i;2A*-2147483646;31;;;~%20;",128,0,0,0 | |
3049 | @end smallexample | |
3050 | ||
3051 | @node Virtual Base Classes | |
3052 | @section Virtual Base Classes | |
3053 | ||
7a292a7a | 3054 | A derived class object consists of a concatenation in memory of the data |
c906108c SS |
3055 | areas defined by each base class, starting with the leftmost and ending |
3056 | with the rightmost in the list of base classes. The exception to this | |
bd79f757 | 3057 | rule is for virtual inheritance. In the example above, class @code{D} |
c906108c SS |
3058 | inherits virtually from base class @code{B}. This means that an |
3059 | instance of a @code{D} object will not contain its own @code{B} part but | |
3060 | merely a pointer to a @code{B} part, known as a virtual base pointer. | |
3061 | ||
3062 | In a derived class stab, the base offset part of the derivation | |
3063 | information, described above, shows how the base class parts are | |
3064 | ordered. The base offset for a virtual base class is always given as 0. | |
3065 | Notice that the base offset for @code{B} is given as 0 even though | |
3066 | @code{B} is not the first base class. The first base class @code{A} | |
3067 | starts at offset 0. | |
3068 | ||
3069 | The field information part of the stab for class @code{D} describes the field | |
3070 | which is the pointer to the virtual base class @code{B}. The vbase pointer | |
3071 | name is @samp{$vb} followed by a type reference to the virtual base class. | |
3072 | Since the type id for @code{B} in this example is 25, the vbase pointer name | |
3073 | is @samp{$vb25}. | |
3074 | ||
3075 | @c FIXME!! fake linebreaks below | |
3076 | @smallexample | |
3077 | .stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat:1, | |
3078 | 160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt::32:i; | |
3079 | 2A*-2147483647;25;;C_virt::32:i;2A*-2147483647;28;;D_virt: | |
3080 | :32:i;2A*-2147483646;31;;;~%20;",128,0,0,0 | |
3081 | @end smallexample | |
3082 | ||
3083 | Following the name and a semicolon is a type reference describing the | |
3084 | type of the virtual base class pointer, in this case 24. Type 24 was | |
3085 | defined earlier as the type of the @code{B} class @code{this} pointer. The | |
3086 | @code{this} pointer for a class is a pointer to the class type. | |
3087 | ||
3088 | @example | |
3089 | .stabs "this:P24=*25=xsB:",64,0,0,8 | |
3090 | @end example | |
3091 | ||
3092 | Finally the field offset part of the vbase pointer field description | |
3093 | shows that the vbase pointer is the first field in the @code{D} object, | |
3094 | before any data fields defined by the class. The layout of a @code{D} | |
3095 | class object is a follows, @code{Adat} at 0, the vtable pointer for | |
3096 | @code{A} at 32, @code{Cdat} at 64, the vtable pointer for C at 96, the | |
3097 | virtual base pointer for @code{B} at 128, and @code{Ddat} at 160. | |
3098 | ||
3099 | ||
3100 | @node Static Members | |
3101 | @section Static Members | |
3102 | ||
3103 | The data area for a class is a concatenation of the space used by the | |
3104 | data members of the class. If the class has virtual methods, a vtable | |
3105 | pointer follows the class data. The field offset part of each field | |
3106 | description in the class stab shows this ordering. | |
3107 | ||
3108 | << How is this reflected in stabs? See Cygnus bug #677 for some info. >> | |
3109 | ||
3110 | @node Stab Types | |
3111 | @appendix Table of Stab Types | |
3112 | ||
3113 | The following are all the possible values for the stab type field, for | |
3114 | a.out files, in numeric order. This does not apply to XCOFF, but | |
3115 | it does apply to stabs in sections (@pxref{Stab Sections}). Stabs in | |
3116 | ECOFF use these values but add 0x8f300 to distinguish them from non-stab | |
3117 | symbols. | |
3118 | ||
3119 | The symbolic names are defined in the file @file{include/aout/stabs.def}. | |
3120 | ||
3121 | @menu | |
3122 | * Non-Stab Symbol Types:: Types from 0 to 0x1f | |
3123 | * Stab Symbol Types:: Types from 0x20 to 0xff | |
3124 | @end menu | |
3125 | ||
3126 | @node Non-Stab Symbol Types | |
3127 | @appendixsec Non-Stab Symbol Types | |
3128 | ||
3129 | The following types are used by the linker and assembler, not by stab | |
3130 | directives. Since this document does not attempt to describe aspects of | |
3131 | object file format other than the debugging format, no details are | |
3132 | given. | |
3133 | ||
3134 | @c Try to get most of these to fit on a single line. | |
3135 | @iftex | |
3136 | @tableindent=1.5in | |
3137 | @end iftex | |
3138 | ||
3139 | @table @code | |
3140 | @item 0x0 N_UNDF | |
3141 | Undefined symbol | |
3142 | ||
3143 | @item 0x2 N_ABS | |
3144 | File scope absolute symbol | |
3145 | ||
3146 | @item 0x3 N_ABS | N_EXT | |
3147 | External absolute symbol | |
3148 | ||
3149 | @item 0x4 N_TEXT | |
3150 | File scope text symbol | |
3151 | ||
3152 | @item 0x5 N_TEXT | N_EXT | |
3153 | External text symbol | |
3154 | ||
3155 | @item 0x6 N_DATA | |
3156 | File scope data symbol | |
3157 | ||
3158 | @item 0x7 N_DATA | N_EXT | |
3159 | External data symbol | |
3160 | ||
3161 | @item 0x8 N_BSS | |
3162 | File scope BSS symbol | |
3163 | ||
3164 | @item 0x9 N_BSS | N_EXT | |
3165 | External BSS symbol | |
3166 | ||
3167 | @item 0x0c N_FN_SEQ | |
3168 | Same as @code{N_FN}, for Sequent compilers | |
3169 | ||
3170 | @item 0x0a N_INDR | |
3171 | Symbol is indirected to another symbol | |
3172 | ||
3173 | @item 0x12 N_COMM | |
3174 | Common---visible after shared library dynamic link | |
3175 | ||
3176 | @item 0x14 N_SETA | |
3177 | @itemx 0x15 N_SETA | N_EXT | |
3178 | Absolute set element | |
3179 | ||
3180 | @item 0x16 N_SETT | |
3181 | @itemx 0x17 N_SETT | N_EXT | |
3182 | Text segment set element | |
3183 | ||
3184 | @item 0x18 N_SETD | |
3185 | @itemx 0x19 N_SETD | N_EXT | |
3186 | Data segment set element | |
3187 | ||
3188 | @item 0x1a N_SETB | |
3189 | @itemx 0x1b N_SETB | N_EXT | |
3190 | BSS segment set element | |
3191 | ||
3192 | @item 0x1c N_SETV | |
3193 | @itemx 0x1d N_SETV | N_EXT | |
3194 | Pointer to set vector | |
3195 | ||
3196 | @item 0x1e N_WARNING | |
3197 | Print a warning message during linking | |
3198 | ||
3199 | @item 0x1f N_FN | |
3200 | File name of a @file{.o} file | |
3201 | @end table | |
3202 | ||
3203 | @node Stab Symbol Types | |
3204 | @appendixsec Stab Symbol Types | |
3205 | ||
3206 | The following symbol types indicate that this is a stab. This is the | |
3207 | full list of stab numbers, including stab types that are used in | |
3208 | languages other than C. | |
3209 | ||
3210 | @table @code | |
3211 | @item 0x20 N_GSYM | |
3212 | Global symbol; see @ref{Global Variables}. | |
3213 | ||
3214 | @item 0x22 N_FNAME | |
3215 | Function name (for BSD Fortran); see @ref{Procedures}. | |
3216 | ||
3217 | @item 0x24 N_FUN | |
3218 | Function name (@pxref{Procedures}) or text segment variable | |
3219 | (@pxref{Statics}). | |
3220 | ||
3221 | @item 0x26 N_STSYM | |
3222 | Data segment file-scope variable; see @ref{Statics}. | |
3223 | ||
3224 | @item 0x28 N_LCSYM | |
3225 | BSS segment file-scope variable; see @ref{Statics}. | |
3226 | ||
3227 | @item 0x2a N_MAIN | |
3228 | Name of main routine; see @ref{Main Program}. | |
3229 | ||
3230 | @item 0x2c N_ROSYM | |
3231 | Variable in @code{.rodata} section; see @ref{Statics}. | |
3232 | ||
3233 | @item 0x30 N_PC | |
3234 | Global symbol (for Pascal); see @ref{N_PC}. | |
3235 | ||
3236 | @item 0x32 N_NSYMS | |
3237 | Number of symbols (according to Ultrix V4.0); see @ref{N_NSYMS}. | |
3238 | ||
3239 | @item 0x34 N_NOMAP | |
3240 | No DST map; see @ref{N_NOMAP}. | |
3241 | ||
3242 | @c FIXME: describe this solaris feature in the body of the text (see | |
3243 | @c comments in include/aout/stab.def). | |
3244 | @item 0x38 N_OBJ | |
3245 | Object file (Solaris2). | |
3246 | ||
3247 | @c See include/aout/stab.def for (a little) more info. | |
3248 | @item 0x3c N_OPT | |
3249 | Debugger options (Solaris2). | |
3250 | ||
3251 | @item 0x40 N_RSYM | |
3252 | Register variable; see @ref{Register Variables}. | |
3253 | ||
3254 | @item 0x42 N_M2C | |
3255 | Modula-2 compilation unit; see @ref{N_M2C}. | |
3256 | ||
3257 | @item 0x44 N_SLINE | |
3258 | Line number in text segment; see @ref{Line Numbers}. | |
3259 | ||
3260 | @item 0x46 N_DSLINE | |
3261 | Line number in data segment; see @ref{Line Numbers}. | |
3262 | ||
3263 | @item 0x48 N_BSLINE | |
3264 | Line number in bss segment; see @ref{Line Numbers}. | |
3265 | ||
3266 | @item 0x48 N_BROWS | |
3267 | Sun source code browser, path to @file{.cb} file; see @ref{N_BROWS}. | |
3268 | ||
3269 | @item 0x4a N_DEFD | |
3270 | GNU Modula2 definition module dependency; see @ref{N_DEFD}. | |
3271 | ||
3272 | @item 0x4c N_FLINE | |
3273 | Function start/body/end line numbers (Solaris2). | |
3274 | ||
3275 | @item 0x50 N_EHDECL | |
3276 | GNU C++ exception variable; see @ref{N_EHDECL}. | |
3277 | ||
3278 | @item 0x50 N_MOD2 | |
3279 | Modula2 info "for imc" (according to Ultrix V4.0); see @ref{N_MOD2}. | |
3280 | ||
3281 | @item 0x54 N_CATCH | |
3282 | GNU C++ @code{catch} clause; see @ref{N_CATCH}. | |
3283 | ||
3284 | @item 0x60 N_SSYM | |
3285 | Structure of union element; see @ref{N_SSYM}. | |
3286 | ||
3287 | @item 0x62 N_ENDM | |
3288 | Last stab for module (Solaris2). | |
3289 | ||
3290 | @item 0x64 N_SO | |
3291 | Path and name of source file; see @ref{Source Files}. | |
3292 | ||
3293 | @item 0x80 N_LSYM | |
3294 | Stack variable (@pxref{Stack Variables}) or type (@pxref{Typedefs}). | |
3295 | ||
3296 | @item 0x82 N_BINCL | |
3297 | Beginning of an include file (Sun only); see @ref{Include Files}. | |
3298 | ||
3299 | @item 0x84 N_SOL | |
3300 | Name of include file; see @ref{Include Files}. | |
3301 | ||
3302 | @item 0xa0 N_PSYM | |
3303 | Parameter variable; see @ref{Parameters}. | |
3304 | ||
3305 | @item 0xa2 N_EINCL | |
3306 | End of an include file; see @ref{Include Files}. | |
3307 | ||
3308 | @item 0xa4 N_ENTRY | |
3309 | Alternate entry point; see @ref{Alternate Entry Points}. | |
3310 | ||
3311 | @item 0xc0 N_LBRAC | |
3312 | Beginning of a lexical block; see @ref{Block Structure}. | |
3313 | ||
3314 | @item 0xc2 N_EXCL | |
3315 | Place holder for a deleted include file; see @ref{Include Files}. | |
3316 | ||
3317 | @item 0xc4 N_SCOPE | |
3318 | Modula2 scope information (Sun linker); see @ref{N_SCOPE}. | |
3319 | ||
3320 | @item 0xe0 N_RBRAC | |
3321 | End of a lexical block; see @ref{Block Structure}. | |
3322 | ||
3323 | @item 0xe2 N_BCOMM | |
3324 | Begin named common block; see @ref{Common Blocks}. | |
3325 | ||
3326 | @item 0xe4 N_ECOMM | |
3327 | End named common block; see @ref{Common Blocks}. | |
3328 | ||
3329 | @item 0xe8 N_ECOML | |
3330 | Member of a common block; see @ref{Common Blocks}. | |
3331 | ||
3332 | @c FIXME: How does this really work? Move it to main body of document. | |
3333 | @item 0xea N_WITH | |
3334 | Pascal @code{with} statement: type,,0,0,offset (Solaris2). | |
3335 | ||
3336 | @item 0xf0 N_NBTEXT | |
3337 | Gould non-base registers; see @ref{Gould}. | |
3338 | ||
3339 | @item 0xf2 N_NBDATA | |
3340 | Gould non-base registers; see @ref{Gould}. | |
3341 | ||
3342 | @item 0xf4 N_NBBSS | |
3343 | Gould non-base registers; see @ref{Gould}. | |
3344 | ||
3345 | @item 0xf6 N_NBSTS | |
3346 | Gould non-base registers; see @ref{Gould}. | |
3347 | ||
3348 | @item 0xf8 N_NBLCS | |
3349 | Gould non-base registers; see @ref{Gould}. | |
3350 | @end table | |
3351 | ||
3352 | @c Restore the default table indent | |
3353 | @iftex | |
3354 | @tableindent=.8in | |
3355 | @end iftex | |
3356 | ||
3357 | @node Symbol Descriptors | |
3358 | @appendix Table of Symbol Descriptors | |
3359 | ||
3360 | The symbol descriptor is the character which follows the colon in many | |
3361 | stabs, and which tells what kind of stab it is. @xref{String Field}, | |
3362 | for more information about their use. | |
3363 | ||
3364 | @c Please keep this alphabetical | |
3365 | @table @code | |
3366 | @c In TeX, this looks great, digit is in italics. But makeinfo insists | |
3367 | @c on putting it in `', not realizing that @var should override @code. | |
3368 | @c I don't know of any way to make makeinfo do the right thing. Seems | |
3369 | @c like a makeinfo bug to me. | |
3370 | @item @var{digit} | |
3371 | @itemx ( | |
3372 | @itemx - | |
3373 | Variable on the stack; see @ref{Stack Variables}. | |
3374 | ||
3375 | @item : | |
085dd6e6 | 3376 | C++ nested symbol; see @xref{Nested Symbols}. |
c906108c SS |
3377 | |
3378 | @item a | |
3379 | Parameter passed by reference in register; see @ref{Reference Parameters}. | |
3380 | ||
3381 | @item b | |
3382 | Based variable; see @ref{Based Variables}. | |
3383 | ||
3384 | @item c | |
3385 | Constant; see @ref{Constants}. | |
3386 | ||
3387 | @item C | |
3388 | Conformant array bound (Pascal, maybe other languages); @ref{Conformant | |
3389 | Arrays}. Name of a caught exception (GNU C++). These can be | |
3390 | distinguished because the latter uses @code{N_CATCH} and the former uses | |
3391 | another symbol type. | |
3392 | ||
3393 | @item d | |
3394 | Floating point register variable; see @ref{Register Variables}. | |
3395 | ||
3396 | @item D | |
3397 | Parameter in floating point register; see @ref{Register Parameters}. | |
3398 | ||
3399 | @item f | |
3400 | File scope function; see @ref{Procedures}. | |
3401 | ||
3402 | @item F | |
3403 | Global function; see @ref{Procedures}. | |
3404 | ||
3405 | @item G | |
3406 | Global variable; see @ref{Global Variables}. | |
3407 | ||
3408 | @item i | |
3409 | @xref{Register Parameters}. | |
3410 | ||
3411 | @item I | |
3412 | Internal (nested) procedure; see @ref{Nested Procedures}. | |
3413 | ||
3414 | @item J | |
3415 | Internal (nested) function; see @ref{Nested Procedures}. | |
3416 | ||
3417 | @item L | |
3418 | Label name (documented by AIX, no further information known). | |
3419 | ||
3420 | @item m | |
3421 | Module; see @ref{Procedures}. | |
3422 | ||
3423 | @item p | |
3424 | Argument list parameter; see @ref{Parameters}. | |
3425 | ||
3426 | @item pP | |
3427 | @xref{Parameters}. | |
3428 | ||
3429 | @item pF | |
3430 | Fortran Function parameter; see @ref{Parameters}. | |
3431 | ||
3432 | @item P | |
3433 | Unfortunately, three separate meanings have been independently invented | |
3434 | for this symbol descriptor. At least the GNU and Sun uses can be | |
3435 | distinguished by the symbol type. Global Procedure (AIX) (symbol type | |
3436 | used unknown); see @ref{Procedures}. Register parameter (GNU) (symbol | |
3437 | type @code{N_PSYM}); see @ref{Parameters}. Prototype of function | |
3438 | referenced by this file (Sun @code{acc}) (symbol type @code{N_FUN}). | |
3439 | ||
3440 | @item Q | |
3441 | Static Procedure; see @ref{Procedures}. | |
3442 | ||
3443 | @item R | |
3444 | Register parameter; see @ref{Register Parameters}. | |
3445 | ||
3446 | @item r | |
3447 | Register variable; see @ref{Register Variables}. | |
3448 | ||
3449 | @item S | |
3450 | File scope variable; see @ref{Statics}. | |
3451 | ||
3452 | @item s | |
3453 | Local variable (OS9000). | |
3454 | ||
3455 | @item t | |
3456 | Type name; see @ref{Typedefs}. | |
3457 | ||
3458 | @item T | |
3459 | Enumeration, structure, or union tag; see @ref{Typedefs}. | |
3460 | ||
3461 | @item v | |
3462 | Parameter passed by reference; see @ref{Reference Parameters}. | |
3463 | ||
3464 | @item V | |
3465 | Procedure scope static variable; see @ref{Statics}. | |
3466 | ||
3467 | @item x | |
3468 | Conformant array; see @ref{Conformant Arrays}. | |
3469 | ||
3470 | @item X | |
3471 | Function return variable; see @ref{Parameters}. | |
3472 | @end table | |
3473 | ||
3474 | @node Type Descriptors | |
3475 | @appendix Table of Type Descriptors | |
3476 | ||
3477 | The type descriptor is the character which follows the type number and | |
3478 | an equals sign. It specifies what kind of type is being defined. | |
3479 | @xref{String Field}, for more information about their use. | |
3480 | ||
3481 | @table @code | |
3482 | @item @var{digit} | |
3483 | @itemx ( | |
3484 | Type reference; see @ref{String Field}. | |
3485 | ||
3486 | @item - | |
3487 | Reference to builtin type; see @ref{Negative Type Numbers}. | |
3488 | ||
3489 | @item # | |
3490 | Method (C++); see @ref{Method Type Descriptor}. | |
3491 | ||
3492 | @item * | |
3493 | Pointer; see @ref{Miscellaneous Types}. | |
3494 | ||
3495 | @item & | |
3496 | Reference (C++). | |
3497 | ||
3498 | @item @@ | |
3499 | Type Attributes (AIX); see @ref{String Field}. Member (class and variable) | |
3500 | type (GNU C++); see @ref{Member Type Descriptor}. | |
3501 | ||
3502 | @item a | |
3503 | Array; see @ref{Arrays}. | |
3504 | ||
3505 | @item A | |
3506 | Open array; see @ref{Arrays}. | |
3507 | ||
3508 | @item b | |
3509 | Pascal space type (AIX); see @ref{Miscellaneous Types}. Builtin integer | |
3510 | type (Sun); see @ref{Builtin Type Descriptors}. Const and volatile | |
bd79f757 | 3511 | qualified type (OS9000). |
c906108c SS |
3512 | |
3513 | @item B | |
3514 | Volatile-qualified type; see @ref{Miscellaneous Types}. | |
3515 | ||
3516 | @item c | |
3517 | Complex builtin type (AIX); see @ref{Builtin Type Descriptors}. | |
3518 | Const-qualified type (OS9000). | |
3519 | ||
3520 | @item C | |
3521 | COBOL Picture type. See AIX documentation for details. | |
3522 | ||
3523 | @item d | |
3524 | File type; see @ref{Miscellaneous Types}. | |
3525 | ||
3526 | @item D | |
3527 | N-dimensional dynamic array; see @ref{Arrays}. | |
3528 | ||
3529 | @item e | |
3530 | Enumeration type; see @ref{Enumerations}. | |
3531 | ||
3532 | @item E | |
3533 | N-dimensional subarray; see @ref{Arrays}. | |
3534 | ||
3535 | @item f | |
3536 | Function type; see @ref{Function Types}. | |
3537 | ||
3538 | @item F | |
3539 | Pascal function parameter; see @ref{Function Types} | |
3540 | ||
3541 | @item g | |
3542 | Builtin floating point type; see @ref{Builtin Type Descriptors}. | |
3543 | ||
3544 | @item G | |
3545 | COBOL Group. See AIX documentation for details. | |
3546 | ||
3547 | @item i | |
3548 | Imported type (AIX); see @ref{Cross-References}. Volatile-qualified | |
3549 | type (OS9000). | |
3550 | ||
3551 | @item k | |
3552 | Const-qualified type; see @ref{Miscellaneous Types}. | |
3553 | ||
3554 | @item K | |
3555 | COBOL File Descriptor. See AIX documentation for details. | |
3556 | ||
3557 | @item M | |
3558 | Multiple instance type; see @ref{Miscellaneous Types}. | |
3559 | ||
3560 | @item n | |
3561 | String type; see @ref{Strings}. | |
3562 | ||
3563 | @item N | |
3564 | Stringptr; see @ref{Strings}. | |
3565 | ||
3566 | @item o | |
3567 | Opaque type; see @ref{Typedefs}. | |
3568 | ||
3569 | @item p | |
3570 | Procedure; see @ref{Function Types}. | |
3571 | ||
3572 | @item P | |
3573 | Packed array; see @ref{Arrays}. | |
3574 | ||
3575 | @item r | |
3576 | Range type; see @ref{Subranges}. | |
3577 | ||
3578 | @item R | |
3579 | Builtin floating type; see @ref{Builtin Type Descriptors} (Sun). Pascal | |
3580 | subroutine parameter; see @ref{Function Types} (AIX). Detecting this | |
3581 | conflict is possible with careful parsing (hint: a Pascal subroutine | |
3582 | parameter type will always contain a comma, and a builtin type | |
3583 | descriptor never will). | |
3584 | ||
3585 | @item s | |
3586 | Structure type; see @ref{Structures}. | |
3587 | ||
3588 | @item S | |
3589 | Set type; see @ref{Miscellaneous Types}. | |
3590 | ||
3591 | @item u | |
3592 | Union; see @ref{Unions}. | |
3593 | ||
3594 | @item v | |
3595 | Variant record. This is a Pascal and Modula-2 feature which is like a | |
3596 | union within a struct in C. See AIX documentation for details. | |
3597 | ||
3598 | @item w | |
3599 | Wide character; see @ref{Builtin Type Descriptors}. | |
3600 | ||
3601 | @item x | |
3602 | Cross-reference; see @ref{Cross-References}. | |
3603 | ||
3604 | @item Y | |
3605 | Used by IBM's xlC C++ compiler (for structures, I think). | |
3606 | ||
3607 | @item z | |
3608 | gstring; see @ref{Strings}. | |
3609 | @end table | |
3610 | ||
3611 | @node Expanded Reference | |
3612 | @appendix Expanded Reference by Stab Type | |
3613 | ||
3614 | @c FIXME: This appendix should go away; see N_PSYM or N_SO for an example. | |
3615 | ||
3616 | For a full list of stab types, and cross-references to where they are | |
3617 | described, see @ref{Stab Types}. This appendix just covers certain | |
3618 | stabs which are not yet described in the main body of this document; | |
3619 | eventually the information will all be in one place. | |
3620 | ||
3621 | Format of an entry: | |
3622 | ||
3623 | The first line is the symbol type (see @file{include/aout/stab.def}). | |
3624 | ||
3625 | The second line describes the language constructs the symbol type | |
3626 | represents. | |
3627 | ||
3628 | The third line is the stab format with the significant stab fields | |
3629 | named and the rest NIL. | |
3630 | ||
3631 | Subsequent lines expand upon the meaning and possible values for each | |
3632 | significant stab field. | |
3633 | ||
3634 | Finally, any further information. | |
3635 | ||
3636 | @menu | |
3637 | * N_PC:: Pascal global symbol | |
3638 | * N_NSYMS:: Number of symbols | |
3639 | * N_NOMAP:: No DST map | |
3640 | * N_M2C:: Modula-2 compilation unit | |
3641 | * N_BROWS:: Path to .cb file for Sun source code browser | |
3642 | * N_DEFD:: GNU Modula2 definition module dependency | |
3643 | * N_EHDECL:: GNU C++ exception variable | |
3644 | * N_MOD2:: Modula2 information "for imc" | |
3645 | * N_CATCH:: GNU C++ "catch" clause | |
3646 | * N_SSYM:: Structure or union element | |
3647 | * N_SCOPE:: Modula2 scope information (Sun only) | |
3648 | * Gould:: non-base register symbols used on Gould systems | |
3649 | * N_LENG:: Length of preceding entry | |
3650 | @end menu | |
3651 | ||
3652 | @node N_PC | |
3653 | @section N_PC | |
3654 | ||
3655 | @deffn @code{.stabs} N_PC | |
3656 | @findex N_PC | |
3657 | Global symbol (for Pascal). | |
3658 | ||
3659 | @example | |
3660 | "name" -> "symbol_name" <<?>> | |
3661 | value -> supposedly the line number (stab.def is skeptical) | |
3662 | @end example | |
3663 | ||
3664 | @display | |
3665 | @file{stabdump.c} says: | |
3666 | ||
3667 | global pascal symbol: name,,0,subtype,line | |
3668 | << subtype? >> | |
3669 | @end display | |
3670 | @end deffn | |
3671 | ||
3672 | @node N_NSYMS | |
3673 | @section N_NSYMS | |
3674 | ||
3675 | @deffn @code{.stabn} N_NSYMS | |
3676 | @findex N_NSYMS | |
3677 | Number of symbols (according to Ultrix V4.0). | |
3678 | ||
3679 | @display | |
3680 | 0, files,,funcs,lines (stab.def) | |
3681 | @end display | |
3682 | @end deffn | |
3683 | ||
3684 | @node N_NOMAP | |
3685 | @section N_NOMAP | |
3686 | ||
3687 | @deffn @code{.stabs} N_NOMAP | |
3688 | @findex N_NOMAP | |
3689 | No DST map for symbol (according to Ultrix V4.0). I think this means a | |
3690 | variable has been optimized out. | |
3691 | ||
3692 | @display | |
3693 | name, ,0,type,ignored (stab.def) | |
3694 | @end display | |
3695 | @end deffn | |
3696 | ||
3697 | @node N_M2C | |
3698 | @section N_M2C | |
3699 | ||
3700 | @deffn @code{.stabs} N_M2C | |
3701 | @findex N_M2C | |
3702 | Modula-2 compilation unit. | |
3703 | ||
3704 | @example | |
3705 | "string" -> "unit_name,unit_time_stamp[,code_time_stamp]" | |
3706 | desc -> unit_number | |
3707 | value -> 0 (main unit) | |
3708 | 1 (any other unit) | |
3709 | @end example | |
3710 | ||
3711 | See @cite{Dbx and Dbxtool Interfaces}, 2nd edition, by Sun, 1988, for | |
3712 | more information. | |
3713 | ||
3714 | @end deffn | |
3715 | ||
3716 | @node N_BROWS | |
3717 | @section N_BROWS | |
3718 | ||
3719 | @deffn @code{.stabs} N_BROWS | |
3720 | @findex N_BROWS | |
3721 | Sun source code browser, path to @file{.cb} file | |
3722 | ||
3723 | <<?>> | |
3724 | "path to associated @file{.cb} file" | |
3725 | ||
3726 | Note: N_BROWS has the same value as N_BSLINE. | |
3727 | @end deffn | |
3728 | ||
3729 | @node N_DEFD | |
3730 | @section N_DEFD | |
3731 | ||
3732 | @deffn @code{.stabn} N_DEFD | |
3733 | @findex N_DEFD | |
3734 | GNU Modula2 definition module dependency. | |
3735 | ||
3736 | GNU Modula-2 definition module dependency. The value is the | |
3737 | modification time of the definition file. The other field is non-zero | |
3738 | if it is imported with the GNU M2 keyword @code{%INITIALIZE}. Perhaps | |
3739 | @code{N_M2C} can be used if there are enough empty fields? | |
3740 | @end deffn | |
3741 | ||
3742 | @node N_EHDECL | |
3743 | @section N_EHDECL | |
3744 | ||
3745 | @deffn @code{.stabs} N_EHDECL | |
3746 | @findex N_EHDECL | |
3747 | GNU C++ exception variable <<?>>. | |
3748 | ||
3749 | "@var{string} is variable name" | |
3750 | ||
3751 | Note: conflicts with @code{N_MOD2}. | |
3752 | @end deffn | |
3753 | ||
3754 | @node N_MOD2 | |
3755 | @section N_MOD2 | |
3756 | ||
3757 | @deffn @code{.stab?} N_MOD2 | |
3758 | @findex N_MOD2 | |
3759 | Modula2 info "for imc" (according to Ultrix V4.0) | |
3760 | ||
3761 | Note: conflicts with @code{N_EHDECL} <<?>> | |
3762 | @end deffn | |
3763 | ||
3764 | @node N_CATCH | |
3765 | @section N_CATCH | |
3766 | ||
3767 | @deffn @code{.stabn} N_CATCH | |
3768 | @findex N_CATCH | |
3769 | GNU C++ @code{catch} clause | |
3770 | ||
3771 | GNU C++ @code{catch} clause. The value is its address. The desc field | |
3772 | is nonzero if this entry is immediately followed by a @code{CAUGHT} stab | |
3773 | saying what exception was caught. Multiple @code{CAUGHT} stabs means | |
3774 | that multiple exceptions can be caught here. If desc is 0, it means all | |
3775 | exceptions are caught here. | |
3776 | @end deffn | |
3777 | ||
3778 | @node N_SSYM | |
3779 | @section N_SSYM | |
3780 | ||
3781 | @deffn @code{.stabn} N_SSYM | |
3782 | @findex N_SSYM | |
3783 | Structure or union element. | |
3784 | ||
3785 | The value is the offset in the structure. | |
3786 | ||
3787 | <<?looking at structs and unions in C I didn't see these>> | |
3788 | @end deffn | |
3789 | ||
3790 | @node N_SCOPE | |
3791 | @section N_SCOPE | |
3792 | ||
3793 | @deffn @code{.stab?} N_SCOPE | |
3794 | @findex N_SCOPE | |
3795 | Modula2 scope information (Sun linker) | |
3796 | <<?>> | |
3797 | @end deffn | |
3798 | ||
3799 | @node Gould | |
3800 | @section Non-base registers on Gould systems | |
3801 | ||
3802 | @deffn @code{.stab?} N_NBTEXT | |
3803 | @deffnx @code{.stab?} N_NBDATA | |
3804 | @deffnx @code{.stab?} N_NBBSS | |
3805 | @deffnx @code{.stab?} N_NBSTS | |
3806 | @deffnx @code{.stab?} N_NBLCS | |
3807 | @findex N_NBTEXT | |
3808 | @findex N_NBDATA | |
3809 | @findex N_NBBSS | |
3810 | @findex N_NBSTS | |
3811 | @findex N_NBLCS | |
3812 | These are used on Gould systems for non-base registers syms. | |
3813 | ||
3814 | However, the following values are not the values used by Gould; they are | |
3815 | the values which GNU has been documenting for these values for a long | |
3816 | time, without actually checking what Gould uses. I include these values | |
3817 | only because perhaps some someone actually did something with the GNU | |
3818 | information (I hope not, why GNU knowingly assigned wrong values to | |
3819 | these in the header file is a complete mystery to me). | |
3820 | ||
3821 | @example | |
3822 | 240 0xf0 N_NBTEXT ?? | |
3823 | 242 0xf2 N_NBDATA ?? | |
3824 | 244 0xf4 N_NBBSS ?? | |
3825 | 246 0xf6 N_NBSTS ?? | |
3826 | 248 0xf8 N_NBLCS ?? | |
3827 | @end example | |
3828 | @end deffn | |
3829 | ||
3830 | @node N_LENG | |
3831 | @section N_LENG | |
3832 | ||
3833 | @deffn @code{.stabn} N_LENG | |
3834 | @findex N_LENG | |
3835 | Second symbol entry containing a length-value for the preceding entry. | |
3836 | The value is the length. | |
3837 | @end deffn | |
3838 | ||
3839 | @node Questions | |
3840 | @appendix Questions and Anomalies | |
3841 | ||
3842 | @itemize @bullet | |
3843 | @item | |
3844 | @c I think this is changed in GCC 2.4.5 to put the line number there. | |
3845 | For GNU C stabs defining local and global variables (@code{N_LSYM} and | |
3846 | @code{N_GSYM}), the desc field is supposed to contain the source | |
3847 | line number on which the variable is defined. In reality the desc | |
3848 | field is always 0. (This behavior is defined in @file{dbxout.c} and | |
3849 | putting a line number in desc is controlled by @samp{#ifdef | |
3850 | WINNING_GDB}, which defaults to false). GDB supposedly uses this | |
3851 | information if you say @samp{list @var{var}}. In reality, @var{var} can | |
3852 | be a variable defined in the program and GDB says @samp{function | |
3853 | @var{var} not defined}. | |
3854 | ||
3855 | @item | |
3856 | In GNU C stabs, there seems to be no way to differentiate tag types: | |
3857 | structures, unions, and enums (symbol descriptor @samp{T}) and typedefs | |
3858 | (symbol descriptor @samp{t}) defined at file scope from types defined locally | |
3859 | to a procedure or other more local scope. They all use the @code{N_LSYM} | |
bd79f757 | 3860 | stab type. Types defined at procedure scope are emitted after the |
c906108c SS |
3861 | @code{N_RBRAC} of the preceding function and before the code of the |
3862 | procedure in which they are defined. This is exactly the same as | |
3863 | types defined in the source file between the two procedure bodies. | |
bd79f757 | 3864 | GDB over-compensates by placing all types in block #1, the block for |
c906108c SS |
3865 | symbols of file scope. This is true for default, @samp{-ansi} and |
3866 | @samp{-traditional} compiler options. (Bugs gcc/1063, gdb/1066.) | |
3867 | ||
3868 | @item | |
3869 | What ends the procedure scope? Is it the proc block's @code{N_RBRAC} or the | |
3870 | next @code{N_FUN}? (I believe its the first.) | |
3871 | @end itemize | |
3872 | ||
3873 | @node Stab Sections | |
3874 | @appendix Using Stabs in Their Own Sections | |
3875 | ||
3876 | Many object file formats allow tools to create object files with custom | |
3877 | sections containing any arbitrary data. For any such object file | |
3878 | format, stabs can be embedded in special sections. This is how stabs | |
3879 | are used with ELF and SOM, and aside from ECOFF and XCOFF, is how stabs | |
3880 | are used with COFF. | |
3881 | ||
3882 | @menu | |
3883 | * Stab Section Basics:: How to embed stabs in sections | |
3884 | * ELF Linker Relocation:: Sun ELF hacks | |
3885 | @end menu | |
3886 | ||
3887 | @node Stab Section Basics | |
3888 | @appendixsec How to Embed Stabs in Sections | |
3889 | ||
3890 | The assembler creates two custom sections, a section named @code{.stab} | |
3891 | which contains an array of fixed length structures, one struct per stab, | |
3892 | and a section named @code{.stabstr} containing all the variable length | |
3893 | strings that are referenced by stabs in the @code{.stab} section. The | |
3894 | byte order of the stabs binary data depends on the object file format. | |
3895 | For ELF, it matches the byte order of the ELF file itself, as determined | |
3896 | from the @code{EI_DATA} field in the @code{e_ident} member of the ELF | |
3897 | header. For SOM, it is always big-endian (is this true??? FIXME). For | |
3898 | COFF, it matches the byte order of the COFF headers. The meaning of the | |
3899 | fields is the same as for a.out (@pxref{Symbol Table Format}), except | |
3900 | that the @code{n_strx} field is relative to the strings for the current | |
3901 | compilation unit (which can be found using the synthetic N_UNDF stab | |
3902 | described below), rather than the entire string table. | |
3903 | ||
3904 | The first stab in the @code{.stab} section for each compilation unit is | |
3905 | synthetic, generated entirely by the assembler, with no corresponding | |
3906 | @code{.stab} directive as input to the assembler. This stab contains | |
3907 | the following fields: | |
3908 | ||
3909 | @table @code | |
3910 | @item n_strx | |
3911 | Offset in the @code{.stabstr} section to the source filename. | |
3912 | ||
3913 | @item n_type | |
3914 | @code{N_UNDF}. | |
3915 | ||
3916 | @item n_other | |
3917 | Unused field, always zero. | |
3918 | This may eventually be used to hold overflows from the count in | |
3919 | the @code{n_desc} field. | |
3920 | ||
3921 | @item n_desc | |
3922 | Count of upcoming symbols, i.e., the number of remaining stabs for this | |
3923 | source file. | |
3924 | ||
3925 | @item n_value | |
3926 | Size of the string table fragment associated with this source file, in | |
3927 | bytes. | |
3928 | @end table | |
3929 | ||
3930 | The @code{.stabstr} section always starts with a null byte (so that string | |
3931 | offsets of zero reference a null string), followed by random length strings, | |
3932 | each of which is null byte terminated. | |
3933 | ||
3934 | The ELF section header for the @code{.stab} section has its | |
3935 | @code{sh_link} member set to the section number of the @code{.stabstr} | |
3936 | section, and the @code{.stabstr} section has its ELF section | |
3937 | header @code{sh_type} member set to @code{SHT_STRTAB} to mark it as a | |
3938 | string table. SOM and COFF have no way of linking the sections together | |
3939 | or marking them as string tables. | |
3940 | ||
3941 | For COFF, the @code{.stab} and @code{.stabstr} sections may be simply | |
3942 | concatenated by the linker. GDB then uses the @code{n_desc} fields to | |
3943 | figure out the extent of the original sections. Similarly, the | |
3944 | @code{n_value} fields of the header symbols are added together in order | |
3945 | to get the actual position of the strings in a desired @code{.stabstr} | |
3946 | section. Although this design obviates any need for the linker to | |
3947 | relocate or otherwise manipulate @code{.stab} and @code{.stabstr} | |
3948 | sections, it also requires some care to ensure that the offsets are | |
3949 | calculated correctly. For instance, if the linker were to pad in | |
3950 | between the @code{.stabstr} sections before concatenating, then the | |
3951 | offsets to strings in the middle of the executable's @code{.stabstr} | |
3952 | section would be wrong. | |
3953 | ||
3954 | The GNU linker is able to optimize stabs information by merging | |
3955 | duplicate strings and removing duplicate header file information | |
3956 | (@pxref{Include Files}). When some versions of the GNU linker optimize | |
3957 | stabs in sections, they remove the leading @code{N_UNDF} symbol and | |
3958 | arranges for all the @code{n_strx} fields to be relative to the start of | |
3959 | the @code{.stabstr} section. | |
3960 | ||
3961 | @node ELF Linker Relocation | |
3962 | @appendixsec Having the Linker Relocate Stabs in ELF | |
3963 | ||
3964 | This section describes some Sun hacks for Stabs in ELF; it does not | |
3965 | apply to COFF or SOM. | |
3966 | ||
3967 | To keep linking fast, you don't want the linker to have to relocate very | |
3968 | many stabs. Making sure this is done for @code{N_SLINE}, | |
3969 | @code{N_RBRAC}, and @code{N_LBRAC} stabs is the most important thing | |
3970 | (see the descriptions of those stabs for more information). But Sun's | |
3971 | stabs in ELF has taken this further, to make all addresses in the | |
3972 | @code{n_value} field (functions and static variables) relative to the | |
3973 | source file. For the @code{N_SO} symbol itself, Sun simply omits the | |
3974 | address. To find the address of each section corresponding to a given | |
3975 | source file, the compiler puts out symbols giving the address of each | |
3976 | section for a given source file. Since these are ELF (not stab) | |
3977 | symbols, the linker relocates them correctly without having to touch the | |
3978 | stabs section. They are named @code{Bbss.bss} for the bss section, | |
3979 | @code{Ddata.data} for the data section, and @code{Drodata.rodata} for | |
3980 | the rodata section. For the text section, there is no such symbol (but | |
3981 | there should be, see below). For an example of how these symbols work, | |
3982 | @xref{Stab Section Transformations}. GCC does not provide these symbols; | |
3983 | it instead relies on the stabs getting relocated. Thus addresses which | |
3984 | would normally be relative to @code{Bbss.bss}, etc., are already | |
3985 | relocated. The Sun linker provided with Solaris 2.2 and earlier | |
3986 | relocates stabs using normal ELF relocation information, as it would do | |
3987 | for any section. Sun has been threatening to kludge their linker to not | |
3988 | do this (to speed up linking), even though the correct way to avoid | |
3989 | having the linker do these relocations is to have the compiler no longer | |
3990 | output relocatable values. Last I heard they had been talked out of the | |
3991 | linker kludge. See Sun point patch 101052-01 and Sun bug 1142109. With | |
3992 | the Sun compiler this affects @samp{S} symbol descriptor stabs | |
3993 | (@pxref{Statics}) and functions (@pxref{Procedures}). In the latter | |
3994 | case, to adopt the clean solution (making the value of the stab relative | |
3995 | to the start of the compilation unit), it would be necessary to invent a | |
3996 | @code{Ttext.text} symbol, analogous to the @code{Bbss.bss}, etc., | |
3997 | symbols. I recommend this rather than using a zero value and getting | |
3998 | the address from the ELF symbols. | |
3999 | ||
4000 | Finding the correct @code{Bbss.bss}, etc., symbol is difficult, because | |
4001 | the linker simply concatenates the @code{.stab} sections from each | |
4002 | @file{.o} file without including any information about which part of a | |
4003 | @code{.stab} section comes from which @file{.o} file. The way GDB does | |
4004 | this is to look for an ELF @code{STT_FILE} symbol which has the same | |
4005 | name as the last component of the file name from the @code{N_SO} symbol | |
4006 | in the stabs (for example, if the file name is @file{../../gdb/main.c}, | |
4007 | it looks for an ELF @code{STT_FILE} symbol named @code{main.c}). This | |
4008 | loses if different files have the same name (they could be in different | |
4009 | directories, a library could have been copied from one system to | |
4010 | another, etc.). It would be much cleaner to have the @code{Bbss.bss} | |
4011 | symbols in the stabs themselves. Having the linker relocate them there | |
4012 | is no more work than having the linker relocate ELF symbols, and it | |
4013 | solves the problem of having to associate the ELF and stab symbols. | |
4014 | However, no one has yet designed or implemented such a scheme. | |
4015 | ||
4016 | @node Symbol Types Index | |
4017 | @unnumbered Symbol Types Index | |
4018 | ||
4019 | @printindex fn | |
4020 | ||
449f3b6c AC |
4021 | @c TeX can handle the contents at the start but makeinfo 3.12 can not |
4022 | @ifinfo | |
c906108c | 4023 | @contents |
449f3b6c AC |
4024 | @end ifinfo |
4025 | @ifhtml | |
4026 | @contents | |
4027 | @end ifhtml | |
4028 | ||
c906108c | 4029 | @bye |