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1 | @c Copyright 2002 |
2 | @c Free Software Foundation, Inc. | |
3 | @c This is part of the GAS manual. | |
4 | @c For copying conditions, see the file as.texinfo. | |
5 | ||
6 | @ifset GENERIC | |
7 | @page | |
8 | @node Alpha-Dependent | |
9 | @chapter Alpha Dependent Features | |
10 | @end ifset | |
11 | ||
12 | @ifclear GENERIC | |
13 | @node Machine Dependencies | |
14 | @chapter Alpha Dependent Features | |
15 | @end ifclear | |
16 | ||
17 | @cindex Alpha support | |
18 | @menu | |
19 | * Alpha Notes:: Notes | |
20 | * Alpha Options:: Options | |
21 | * Alpha Syntax:: Syntax | |
22 | * Alpha Floating Point:: Floating Point | |
23 | * Alpha Directives:: Alpha Machine Directives | |
24 | * Alpha Opcodes:: Opcodes | |
25 | @end menu | |
26 | ||
27 | @node Alpha Notes | |
28 | @section Notes | |
29 | @cindex Alpha notes | |
30 | @cindex notes for Alpha | |
31 | ||
32 | The documentation here is primarily for the ELF object format. | |
33 | @code{@value{AS}} also supports the ECOFF and EVAX formats, but | |
34 | features specific to these formats are not yet documented. | |
35 | ||
36 | @node Alpha Options | |
37 | @section Options | |
38 | @cindex Alpha options | |
39 | @cindex options for Alpha | |
40 | ||
41 | @table @option | |
42 | @cindex @code{-m@var{cpu}} command line option, Alpha | |
43 | @item -m@var{cpu} | |
44 | This option specifies the target processor. If an attempt is made to | |
45 | assemble an instruction which will not execute on the target processor, | |
46 | the assembler may either expand the instruction as a macro or issue an | |
47 | error message. This option is equivalent to the @code{.arch} directive. | |
48 | ||
49 | The following processor names are recognized: | |
50 | @code{21064}, | |
51 | @code{21064a}, | |
52 | @code{21066}, | |
53 | @code{21068}, | |
54 | @code{21164}, | |
55 | @code{21164a}, | |
56 | @code{21164pc}, | |
57 | @code{21264}, | |
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58 | @code{21264a}, |
59 | @code{21264b}, | |
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60 | @code{ev4}, |
61 | @code{ev5}, | |
62 | @code{lca45}, | |
63 | @code{ev5}, | |
64 | @code{ev56}, | |
65 | @code{pca56}, | |
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66 | @code{ev6}, |
67 | @code{ev67}, | |
68 | @code{ev68}. | |
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69 | The special name @code{all} may be used to allow the assembler to accept |
70 | instructions valid for any Alpha processor. | |
71 | ||
72 | In order to support existing practice in OSF/1 with respect to @code{.arch}, | |
73 | and existing practice within @command{MILO} (the Linux ARC bootloader), the | |
74 | numbered processor names (e.g.@: 21064) enable the processor-specific PALcode | |
75 | instructions, while the ``electro-vlasic'' names (e.g.@: @code{ev4}) do not. | |
76 | ||
77 | @cindex @code{-mdebug} command line option, Alpha | |
78 | @cindex @code{-no-mdebug} command line option, Alpha | |
79 | @item -mdebug | |
80 | @itemx -no-mdebug | |
81 | Enables or disables the generation of @code{.mdebug} encapsulation for | |
82 | stabs directives and procedure descriptors. The default is to automatically | |
83 | enable @code{.mdebug} when the first stabs directive is seen. | |
84 | ||
85 | @cindex @code{-relax} command line option, Alpha | |
86 | @item -relax | |
87 | This option forces all relocations to be put into the object file, instead | |
88 | of saving space and resolving some relocations at assembly time. Note that | |
89 | this option does not propagate all symbol arithmetic into the object file, | |
90 | because not all symbol arithmetic can be represented. However, the option | |
91 | can still be useful in specific applications. | |
92 | ||
93 | @cindex @code{-g} command line option, Alpha | |
94 | @item -g | |
95 | This option is used when the compiler generates debug information. When | |
96 | @command{gcc} is using @command{mips-tfile} to generate debug | |
97 | information for ECOFF, local labels must be passed through to the object | |
98 | file. Otherwise this option has no effect. | |
99 | ||
100 | @cindex @code{-G} command line option, Alpha | |
101 | @item -G@var{size} | |
102 | A local common symbol larger than @var{size} is placed in @code{.bss}, | |
103 | while smaller symbols are placed in @code{.sbss}. | |
104 | ||
105 | @cindex @code{-F} command line option, Alpha | |
106 | @cindex @code{-32addr} command line option, Alpha | |
107 | @item -F | |
108 | @itemx -32addr | |
109 | These options are ignored for backward compatibility. | |
110 | @end table | |
111 | ||
112 | @cindex Alpha Syntax | |
113 | @node Alpha Syntax | |
114 | @section Syntax | |
115 | The assembler syntax closely follow the Alpha Reference Manual; | |
116 | assembler directives and general syntax closely follow the OSF/1 and | |
117 | OpenVMS syntax, with a few differences for ELF. | |
118 | ||
119 | @menu | |
120 | * Alpha-Chars:: Special Characters | |
121 | * Alpha-Regs:: Register Names | |
122 | * Alpha-Relocs:: Relocations | |
123 | @end menu | |
124 | ||
125 | @node Alpha-Chars | |
126 | @subsection Special Characters | |
127 | ||
128 | @cindex line comment character, Alpha | |
129 | @cindex Alpha line comment character | |
130 | @samp{#} is the line comment character. | |
131 | ||
132 | @cindex line separator, Alpha | |
133 | @cindex statement separator, Alpha | |
134 | @cindex Alpha line separator | |
135 | @samp{;} can be used instead of a newline to separate statements. | |
136 | ||
137 | @node Alpha-Regs | |
138 | @subsection Register Names | |
139 | @cindex Alpha registers | |
140 | @cindex register names, Alpha | |
141 | ||
142 | The 32 integer registers are refered to as @samp{$@var{n}} or | |
143 | @samp{$r@var{n}}. In addition, registers 15, 28, 29, and 30 may | |
144 | be refered to by the symbols @samp{$fp}, @samp{$at}, @samp{$gp}, | |
145 | and @samp{$sp} respectively. | |
146 | ||
147 | The 32 floating-point registers are refered to as @samp{$f@var{n}}. | |
148 | ||
149 | @node Alpha-Relocs | |
150 | @subsection Relocations | |
151 | @cindex Alpha relocations | |
152 | @cindex relocations, Alpha | |
153 | ||
154 | Some of these relocations are available for ECOFF, but mostly | |
155 | only for ELF. They are modeled after the relocation format | |
156 | introduced in Digial Unix 4.0, but there are additions. | |
157 | ||
158 | The format is @samp{!@var{tag}} or @samp{!@var{tag}!@var{number}} | |
159 | where @var{tag} is the name of the relocation. In some cases | |
160 | @var{number} is used to relate specific instructions. | |
161 | ||
162 | The relocation is placed at the end of the instruction like so: | |
163 | ||
164 | @example | |
165 | ldah $0,a($29) !gprelhigh | |
166 | lda $0,a($0) !gprellow | |
167 | ldq $1,b($29) !literal!100 | |
168 | ldl $2,0($1) !lituse_base!100 | |
169 | @end example | |
170 | ||
171 | @table @code | |
172 | @item !literal | |
173 | @itemx !literal!@var{N} | |
174 | Used with an @code{ldq} instruction to load the address of a symbol | |
175 | from the GOT. | |
176 | ||
177 | A sequence number @var{N} is optional, and if present is used to pair | |
178 | @code{lituse} relocations with this @code{literal} relocation. The | |
179 | @code{lituse} relocations are used by the linker to optimize the code | |
180 | based on the final location of the symbol. | |
181 | ||
182 | Note that these optimizations are dependent on the data flow of the | |
183 | program. Therefore, if @emph{any} @code{lituse} is paired with a | |
184 | @code{literal} relocation, then @emph{all} uses of the register set by | |
185 | the @code{literal} instruction must also be marked with @code{lituse} | |
186 | relocations. This is because the original @code{literal} instruction | |
187 | may be deleted or transformed into another instruction. | |
188 | ||
189 | Also note that there may be a one-to-many relationship between | |
190 | @code{literal} and @code{lituse}, but not a many-to-one. That is, if | |
191 | there are two code paths that load up the same address and feed the | |
192 | value to a single use, then the use may not use a @code{lituse} | |
193 | relocation. | |
194 | ||
195 | @item !lituse_base!@var{N} | |
196 | Used with any memory format instruction (e.g.@: @code{ldl}) to indicate | |
197 | that the literal is used for an address load. The offset field of the | |
198 | instruction must be zero. During relaxation, the code may be altered | |
199 | to use a gp-relative load. | |
200 | ||
201 | @item !lituse_jsr!@var{N} | |
202 | Used with a register branch format instruction (e.g.@: @code{jsr}) to | |
203 | indicate that the literal is used for a call. During relaxation, the | |
204 | code may be altered to use a direct branch (e.g.@: @code{bsr}). | |
205 | ||
206 | @item !lituse_bytoff!@var{N} | |
207 | Used with a byte mask instruction (e.g.@: @code{extbl}) to indicate | |
208 | that only the low 3 bits of the address are relevant. During relaxation, | |
209 | the code may be altered to use an immediate instead of a register shift. | |
210 | ||
211 | @item !lituse_addr!@var{N} | |
212 | Used with any other instruction to indicate that the original address | |
213 | is in fact used, and the original @code{ldq} instruction may not be | |
214 | altered or deleted. This is useful in conjunction with @code{lituse_jsr} | |
215 | to test whether a weak symbol is defined. | |
216 | ||
217 | @example | |
218 | ldq $27,foo($29) !literal!1 | |
219 | beq $27,is_undef !lituse_addr!1 | |
220 | jsr $26,($27),foo !lituse_jsr!1 | |
221 | @end example | |
222 | ||
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223 | @item !lituse_tlsgd!@var{N} |
224 | Used with a register branch format instruction to indicate that the | |
225 | literal is the call to @code{__tls_get_addr} used to compute the | |
226 | address of the thread-local storage variable whose descriptor was | |
227 | loaded with @code{!tlsgd!@var{N}}. | |
228 | ||
229 | @item !lituse_tlsldm!@var{N} | |
230 | Used with a register branch format instruction to indicate that the | |
231 | literal is the call to @code{__tls_get_addr} used to compute the | |
232 | address of the base of the thread-local storage block for the current | |
233 | module. The descriptor for the module must have been loaded with | |
234 | @code{!tlsldm!@var{N}}. | |
235 | ||
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236 | @item !gpdisp!@var{N} |
237 | Used with @code{ldah} and @code{lda} to load the GP from the current | |
238 | address, a-la the @code{ldgp} macro. The source register for the | |
239 | @code{ldah} instruction must contain the address of the @code{ldah} | |
240 | instruction. There must be exactly one @code{lda} instruction paired | |
241 | with the @code{ldah} instruction, though it may appear anywhere in | |
242 | the instruction stream. The immediate operands must be zero. | |
243 | ||
244 | @example | |
245 | bsr $26,foo | |
246 | ldah $29,0($26) !gpdisp!1 | |
247 | lda $29,0($29) !gpdisp!1 | |
248 | @end example | |
249 | ||
250 | @item !gprelhigh | |
251 | Used with an @code{ldah} instruction to add the high 16 bits of a | |
252 | 32-bit displacement from the GP. | |
253 | ||
254 | @item !gprellow | |
255 | Used with any memory format instruction to add the low 16 bits of a | |
256 | 32-bit displacement from the GP. | |
257 | ||
258 | @item !gprel | |
259 | Used with any memory format instruction to add a 16-bit displacement | |
260 | from the GP. | |
261 | ||
262 | @item !samegp | |
263 | Used with any branch format instruction to skip the GP load at the | |
264 | target address. The referenced symbol must have the same GP as the | |
265 | source object file, and it must be declared to either not use @code{$27} | |
266 | or perform a standard GP load in the first two instructions via the | |
267 | @code{.prologue} directive. | |
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268 | |
269 | @item !tlsgd | |
270 | @itemx !tlsgd!@var{N} | |
271 | Used with an @code{lda} instruction to load the address of a TLS | |
272 | descriptor for a symbol in the GOT. | |
273 | ||
274 | The sequence number @var{N} is optional, and if present it used to | |
275 | pair the descriptor load with both the @code{literal} loading the | |
276 | address of the @code{__tls_get_addr} function and the @code{lituse_tlsgd} | |
277 | marking the call to that function. | |
278 | ||
279 | For proper relaxation, both the @code{tlsgd}, @code{literal} and | |
280 | @code{lituse} relocations must be in the same extended basic block. | |
281 | That is, the relocation with the lowest address must be executed | |
282 | first at runtime. | |
283 | ||
284 | @item !tlsldm | |
285 | @itemx !tlsldm!@var{N} | |
286 | Used with an @code{lda} instruction to load the address of a TLS | |
287 | descriptor for the current module in the GOT. | |
288 | ||
289 | Similar in other respects to @code{tlsgd}. | |
290 | ||
291 | @item !gotdtprel | |
292 | Used with an @code{ldq} instruction to load the offset of the TLS | |
293 | symbol within its module's thread-local storage block. Also known | |
294 | as the dynamic thread pointer offset or dtp-relative offset. | |
295 | ||
296 | @item !dtprelhi | |
297 | @itemx !dtprello | |
298 | @itemx !dtprel | |
299 | Like @code{gprel} relocations except they compute dtp-relative offsets. | |
300 | ||
301 | @item !gottprel | |
302 | Used with an @code{ldq} instruction to load the offset of the TLS | |
303 | symbol from the thread pointer. Also known as the tp-relative offset. | |
304 | ||
305 | @item !tprelhi | |
306 | @itemx !tprello | |
307 | @itemx !tprel | |
308 | Like @code{gprel} relocations except they compute tp-relative offsets. | |
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309 | @end table |
310 | ||
311 | @node Alpha Floating Point | |
312 | @section Floating Point | |
313 | @cindex floating point, Alpha (@sc{ieee}) | |
314 | @cindex Alpha floating point (@sc{ieee}) | |
315 | The Alpha family uses both @sc{ieee} and VAX floating-point numbers. | |
316 | ||
317 | @node Alpha Directives | |
318 | @section Alpha Assembler Directives | |
319 | ||
320 | @command{@value{AS}} for the Alpha supports many additional directives for | |
321 | compatibility with the native assembler. This section describes them only | |
322 | briefly. | |
323 | ||
324 | @cindex Alpha-only directives | |
325 | These are the additional directives in @code{@value{AS}} for the Alpha: | |
326 | ||
327 | @table @code | |
328 | @item .arch @var{cpu} | |
329 | Specifies the target processor. This is equivalent to the | |
330 | @option{-m@var{cpu}} command-line option. @xref{Alpha Options, Options}, | |
331 | for a list of values for @var{cpu}. | |
332 | ||
333 | @item .ent @var{function}[, @var{n}] | |
334 | Mark the beginning of @var{function}. An optional number may follow for | |
335 | compatibility with the OSF/1 assembler, but is ignored. When generating | |
336 | @code{.mdebug} information, this will create a procedure descriptor for | |
337 | the function. In ELF, it will mark the symbol as a function a-la the | |
338 | generic @code{.type} directive. | |
339 | ||
340 | @item .end @var{function} | |
341 | Mark the end of @var{function}. In ELF, it will set the size of the symbol | |
342 | a-la the generic @code{.size} directive. | |
343 | ||
344 | @item .mask @var{mask}, @var{offset} | |
345 | Indicate which of the integer registers are saved in the current | |
346 | function's stack frame. @var{mask} is interpreted a bit mask in which | |
347 | bit @var{n} set indicates that register @var{n} is saved. The registers | |
348 | are saved in a block located @var{offset} bytes from the @dfn{canonical | |
349 | frame address} (CFA) which is the value of the stack pointer on entry to | |
350 | the function. The registers are saved sequentially, except that the | |
351 | return address register (normally @code{$26}) is saved first. | |
352 | ||
353 | This and the other directives that describe the stack frame are | |
354 | currently only used when generating @code{.mdebug} information. They | |
355 | may in the future be used to generate DWARF2 @code{.debug_frame} unwind | |
356 | information for hand written assembly. | |
357 | ||
358 | @item .fmask @var{mask}, @var{offset} | |
359 | Indicate which of the floating-point registers are saved in the current | |
360 | stack frame. The @var{mask} and @var{offset} parameters are interpreted | |
361 | as with @code{.mask}. | |
362 | ||
363 | @item .frame @var{framereg}, @var{frameoffset}, @var{retreg}[, @var{argoffset}] | |
364 | Describes the shape of the stack frame. The frame pointer in use is | |
365 | @var{framereg}; normally this is either @code{$fp} or @code{$sp}. The | |
366 | frame pointer is @var{frameoffset} bytes below the CFA. The return | |
367 | address is initially located in @var{retreg} until it is saved as | |
368 | indicated in @code{.mask}. For compatibility with OSF/1 an optional | |
369 | @var{argoffset} parameter is accepted and ignored. It is believed to | |
370 | indicate the offset from the CFA to the saved argument registers. | |
371 | ||
372 | @item .prologue @var{n} | |
373 | Indicate that the stack frame is set up and all registers have been | |
374 | spilled. The argument @var{n} indicates whether and how the function | |
375 | uses the incoming @dfn{procedure vector} (the address of the called | |
376 | function) in @code{$27}. 0 indicates that @code{$27} is not used; 1 | |
377 | indicates that the first two instructions of the function use @code{$27} | |
378 | to perform a load of the GP register; 2 indicates that @code{$27} is | |
379 | used in some non-standard way and so the linker cannot elide the load of | |
380 | the procedure vector during relaxation. | |
381 | ||
382 | @item .gprel32 @var{expression} | |
383 | Computes the difference between the address in @var{expression} and the | |
384 | GP for the current object file, and stores it in 4 bytes. In addition | |
385 | to being smaller than a full 8 byte address, this also does not require | |
386 | a dynamic relocation when used in a shared library. | |
387 | ||
388 | @item .t_floating @var{expression} | |
389 | Stores @var{expression} as an @sc{ieee} double precision value. | |
390 | ||
391 | @item .s_floating @var{expression} | |
392 | Stores @var{expression} as an @sc{ieee} single precision value. | |
393 | ||
394 | @item .f_floating @var{expression} | |
395 | Stores @var{expression} as a VAX F format value. | |
396 | ||
397 | @item .g_floating @var{expression} | |
398 | Stores @var{expression} as a VAX G format value. | |
399 | ||
400 | @item .d_floating @var{expression} | |
401 | Stores @var{expression} as a VAX D format value. | |
402 | ||
403 | @item .set @var{feature} | |
404 | Enables or disables various assembler features. Using the positive | |
405 | name of the feature enables while using @samp{no@var{feature}} disables. | |
406 | ||
407 | @table @code | |
408 | @item at | |
409 | Indicates that macro expansions may clobber the @dfn{assembler | |
410 | temporary} (@code{$at} or @code{$28}) register. Some macros may not be | |
411 | expanded without this and will generate an error message if @code{noat} | |
412 | is in effect. When @code{at} is in effect, a warning will be generated | |
413 | if @code{$at} is used by the programmer. | |
414 | ||
415 | @item macro | |
416 | Enables the expasion of macro instructions. Note that variants of real | |
417 | instructions, such as @code{br label} vs @code{br $31,label} are | |
418 | considered alternate forms and not macros. | |
419 | ||
420 | @item move | |
421 | @itemx reorder | |
422 | @itemx volatile | |
423 | These control whether and how the assembler may re-order instructions. | |
424 | Accepted for compatibility with the OSF/1 assembler, but @command{@value{AS}} | |
425 | does not do instruction scheduling, so these features are ignored. | |
426 | @end table | |
427 | @end table | |
428 | ||
429 | The following directives are recognized for compatibility with the OSF/1 | |
430 | assembler but are ignored. | |
431 | ||
432 | @example | |
433 | .proc .aproc | |
434 | .reguse .livereg | |
435 | .option .aent | |
436 | .ugen .eflag | |
437 | .alias .noalias | |
438 | @end example | |
439 | ||
440 | @node Alpha Opcodes | |
441 | @section Opcodes | |
442 | For detailed information on the Alpha machine instruction set, see the | |
443 | @c Attempt to work around a very overfull hbox. | |
444 | @iftex | |
445 | Alpha Architecture Handbook located at | |
446 | @smallfonts | |
447 | @example | |
448 | ftp://ftp.digital.com/pub/Digital/info/semiconductor/literature/alphaahb.pdf | |
449 | @end example | |
450 | @textfonts | |
451 | @end iftex | |
452 | @ifnottex | |
453 | @uref{ftp://ftp.digital.com/pub/Digital/info/semiconductor/literature/alphaahb.pdf,Alpha Architecture Handbook}. | |
454 | @end ifnottex |