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faf5f7ad SB |
1 | /* GNU/Linux on ARM target support. |
2 | Copyright 1999, 2000 Free Software Foundation, Inc. | |
3 | ||
4 | This file is part of GDB. | |
5 | ||
6 | This program is free software; you can redistribute it and/or modify | |
7 | it under the terms of the GNU General Public License as published by | |
8 | the Free Software Foundation; either version 2 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | This program is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | GNU General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU General Public License | |
17 | along with this program; if not, write to the Free Software | |
18 | Foundation, Inc., 59 Temple Place - Suite 330, | |
19 | Boston, MA 02111-1307, USA. */ | |
20 | ||
21 | #include "defs.h" | |
c20f6dea SB |
22 | #include "target.h" |
23 | #include "value.h" | |
faf5f7ad | 24 | #include "gdbtypes.h" |
134e61c4 | 25 | #include "floatformat.h" |
faf5f7ad | 26 | |
a52e6aac SB |
27 | /* For arm_linux_skip_solib_resolver. */ |
28 | #include "symtab.h" | |
29 | #include "symfile.h" | |
30 | #include "objfiles.h" | |
31 | ||
faf5f7ad SB |
32 | #ifdef GET_LONGJMP_TARGET |
33 | ||
34 | /* Figure out where the longjmp will land. We expect that we have | |
35 | just entered longjmp and haven't yet altered r0, r1, so the | |
36 | arguments are still in the registers. (A1_REGNUM) points at the | |
37 | jmp_buf structure from which we extract the pc (JB_PC) that we will | |
38 | land at. The pc is copied into ADDR. This routine returns true on | |
39 | success. */ | |
40 | ||
41 | #define LONGJMP_TARGET_SIZE sizeof(int) | |
42 | #define JB_ELEMENT_SIZE sizeof(int) | |
43 | #define JB_SL 18 | |
44 | #define JB_FP 19 | |
45 | #define JB_SP 20 | |
46 | #define JB_PC 21 | |
47 | ||
48 | int | |
49 | arm_get_longjmp_target (CORE_ADDR * pc) | |
50 | { | |
51 | CORE_ADDR jb_addr; | |
52 | char buf[LONGJMP_TARGET_SIZE]; | |
53 | ||
54 | jb_addr = read_register (A1_REGNUM); | |
55 | ||
56 | if (target_read_memory (jb_addr + JB_PC * JB_ELEMENT_SIZE, buf, | |
57 | LONGJMP_TARGET_SIZE)) | |
58 | return 0; | |
59 | ||
60 | *pc = extract_address (buf, LONGJMP_TARGET_SIZE); | |
61 | return 1; | |
62 | } | |
63 | ||
64 | #endif /* GET_LONGJMP_TARGET */ | |
65 | ||
66 | /* Extract from an array REGBUF containing the (raw) register state | |
67 | a function return value of type TYPE, and copy that, in virtual format, | |
68 | into VALBUF. */ | |
69 | ||
70 | void | |
71 | arm_linux_extract_return_value (struct type *type, | |
72 | char regbuf[REGISTER_BYTES], | |
73 | char *valbuf) | |
74 | { | |
75 | /* ScottB: This needs to be looked at to handle the different | |
76 | floating point emulators on ARM Linux. Right now the code | |
77 | assumes that fetch inferior registers does the right thing for | |
78 | GDB. I suspect this won't handle NWFPE registers correctly, nor | |
79 | will the default ARM version (arm_extract_return_value()). */ | |
80 | ||
81 | int regnum = (TYPE_CODE_FLT == TYPE_CODE (type)) ? F0_REGNUM : A1_REGNUM; | |
82 | memcpy (valbuf, ®buf[REGISTER_BYTE (regnum)], TYPE_LENGTH (type)); | |
83 | } | |
84 | ||
134e61c4 SB |
85 | /* Note: ScottB |
86 | ||
87 | This function does not support passing parameters using the FPA | |
88 | variant of the APCS. It passes any floating point arguments in the | |
89 | general registers and/or on the stack. | |
90 | ||
91 | FIXME: This and arm_push_arguments should be merged. However this | |
92 | function breaks on a little endian host, big endian target | |
93 | using the COFF file format. ELF is ok. | |
94 | ||
95 | ScottB. */ | |
96 | ||
97 | /* Addresses for calling Thumb functions have the bit 0 set. | |
98 | Here are some macros to test, set, or clear bit 0 of addresses. */ | |
99 | #define IS_THUMB_ADDR(addr) ((addr) & 1) | |
100 | #define MAKE_THUMB_ADDR(addr) ((addr) | 1) | |
101 | #define UNMAKE_THUMB_ADDR(addr) ((addr) & ~1) | |
102 | ||
103 | CORE_ADDR | |
104 | arm_linux_push_arguments (int nargs, value_ptr * args, CORE_ADDR sp, | |
105 | int struct_return, CORE_ADDR struct_addr) | |
106 | { | |
107 | char *fp; | |
108 | int argnum, argreg, nstack_size; | |
109 | ||
110 | /* Walk through the list of args and determine how large a temporary | |
111 | stack is required. Need to take care here as structs may be | |
112 | passed on the stack, and we have to to push them. */ | |
113 | nstack_size = -4 * REGISTER_SIZE; /* Some arguments go into A1-A4. */ | |
114 | ||
115 | if (struct_return) /* The struct address goes in A1. */ | |
116 | nstack_size += REGISTER_SIZE; | |
117 | ||
118 | /* Walk through the arguments and add their size to nstack_size. */ | |
119 | for (argnum = 0; argnum < nargs; argnum++) | |
120 | { | |
121 | int len; | |
122 | struct type *arg_type; | |
123 | ||
124 | arg_type = check_typedef (VALUE_TYPE (args[argnum])); | |
125 | len = TYPE_LENGTH (arg_type); | |
126 | ||
127 | /* ANSI C code passes float arguments as integers, K&R code | |
128 | passes float arguments as doubles. Correct for this here. */ | |
129 | if (TYPE_CODE_FLT == TYPE_CODE (arg_type) && REGISTER_SIZE == len) | |
130 | nstack_size += FP_REGISTER_VIRTUAL_SIZE; | |
131 | else | |
132 | nstack_size += len; | |
133 | } | |
134 | ||
135 | /* Allocate room on the stack, and initialize our stack frame | |
136 | pointer. */ | |
137 | fp = NULL; | |
138 | if (nstack_size > 0) | |
139 | { | |
140 | sp -= nstack_size; | |
141 | fp = (char *) sp; | |
142 | } | |
143 | ||
144 | /* Initialize the integer argument register pointer. */ | |
145 | argreg = A1_REGNUM; | |
146 | ||
147 | /* The struct_return pointer occupies the first parameter passing | |
148 | register. */ | |
149 | if (struct_return) | |
150 | write_register (argreg++, struct_addr); | |
151 | ||
152 | /* Process arguments from left to right. Store as many as allowed | |
153 | in the parameter passing registers (A1-A4), and save the rest on | |
154 | the temporary stack. */ | |
155 | for (argnum = 0; argnum < nargs; argnum++) | |
156 | { | |
157 | int len; | |
158 | char *val; | |
159 | double dbl_arg; | |
160 | CORE_ADDR regval; | |
161 | enum type_code typecode; | |
162 | struct type *arg_type, *target_type; | |
163 | ||
164 | arg_type = check_typedef (VALUE_TYPE (args[argnum])); | |
165 | target_type = TYPE_TARGET_TYPE (arg_type); | |
166 | len = TYPE_LENGTH (arg_type); | |
167 | typecode = TYPE_CODE (arg_type); | |
168 | val = (char *) VALUE_CONTENTS (args[argnum]); | |
169 | ||
170 | /* ANSI C code passes float arguments as integers, K&R code | |
171 | passes float arguments as doubles. The .stabs record for | |
172 | for ANSI prototype floating point arguments records the | |
173 | type as FP_INTEGER, while a K&R style (no prototype) | |
174 | .stabs records the type as FP_FLOAT. In this latter case | |
175 | the compiler converts the float arguments to double before | |
176 | calling the function. */ | |
177 | if (TYPE_CODE_FLT == typecode && REGISTER_SIZE == len) | |
178 | { | |
179 | /* Float argument in buffer is in host format. Read it and | |
180 | convert to DOUBLEST, and store it in target double. */ | |
181 | DOUBLEST dblval; | |
182 | ||
183 | len = TARGET_DOUBLE_BIT / TARGET_CHAR_BIT; | |
184 | floatformat_to_doublest (HOST_FLOAT_FORMAT, val, &dblval); | |
185 | store_floating (&dbl_arg, len, dblval); | |
186 | val = (char *) &dbl_arg; | |
187 | } | |
188 | ||
189 | /* If the argument is a pointer to a function, and it is a Thumb | |
190 | function, set the low bit of the pointer. */ | |
191 | if (TYPE_CODE_PTR == typecode | |
192 | && NULL != target_type | |
193 | && TYPE_CODE_FUNC == TYPE_CODE (target_type)) | |
194 | { | |
195 | CORE_ADDR regval = extract_address (val, len); | |
196 | if (arm_pc_is_thumb (regval)) | |
197 | store_address (val, len, MAKE_THUMB_ADDR (regval)); | |
198 | } | |
199 | ||
200 | /* Copy the argument to general registers or the stack in | |
201 | register-sized pieces. Large arguments are split between | |
202 | registers and stack. */ | |
203 | while (len > 0) | |
204 | { | |
205 | int partial_len = len < REGISTER_SIZE ? len : REGISTER_SIZE; | |
206 | ||
207 | if (argreg <= ARM_LAST_ARG_REGNUM) | |
208 | { | |
209 | /* It's an argument being passed in a general register. */ | |
210 | regval = extract_address (val, partial_len); | |
211 | write_register (argreg++, regval); | |
212 | } | |
213 | else | |
214 | { | |
215 | /* Push the arguments onto the stack. */ | |
216 | write_memory ((CORE_ADDR) fp, val, REGISTER_SIZE); | |
217 | fp += REGISTER_SIZE; | |
218 | } | |
219 | ||
220 | len -= partial_len; | |
221 | val += partial_len; | |
222 | } | |
223 | } | |
224 | ||
225 | /* Return adjusted stack pointer. */ | |
226 | return sp; | |
227 | } | |
228 | ||
f38e884d SB |
229 | /* |
230 | Dynamic Linking on ARM Linux | |
231 | ---------------------------- | |
232 | ||
233 | Note: PLT = procedure linkage table | |
234 | GOT = global offset table | |
235 | ||
236 | As much as possible, ELF dynamic linking defers the resolution of | |
237 | jump/call addresses until the last minute. The technique used is | |
238 | inspired by the i386 ELF design, and is based on the following | |
239 | constraints. | |
240 | ||
241 | 1) The calling technique should not force a change in the assembly | |
242 | code produced for apps; it MAY cause changes in the way assembly | |
243 | code is produced for position independent code (i.e. shared | |
244 | libraries). | |
245 | ||
246 | 2) The technique must be such that all executable areas must not be | |
247 | modified; and any modified areas must not be executed. | |
248 | ||
249 | To do this, there are three steps involved in a typical jump: | |
250 | ||
251 | 1) in the code | |
252 | 2) through the PLT | |
253 | 3) using a pointer from the GOT | |
254 | ||
255 | When the executable or library is first loaded, each GOT entry is | |
256 | initialized to point to the code which implements dynamic name | |
257 | resolution and code finding. This is normally a function in the | |
258 | program interpreter (on ARM Linux this is usually ld-linux.so.2, | |
259 | but it does not have to be). On the first invocation, the function | |
260 | is located and the GOT entry is replaced with the real function | |
261 | address. Subsequent calls go through steps 1, 2 and 3 and end up | |
262 | calling the real code. | |
263 | ||
264 | 1) In the code: | |
265 | ||
266 | b function_call | |
267 | bl function_call | |
268 | ||
269 | This is typical ARM code using the 26 bit relative branch or branch | |
270 | and link instructions. The target of the instruction | |
271 | (function_call is usually the address of the function to be called. | |
272 | In position independent code, the target of the instruction is | |
273 | actually an entry in the PLT when calling functions in a shared | |
274 | library. Note that this call is identical to a normal function | |
275 | call, only the target differs. | |
276 | ||
277 | 2) In the PLT: | |
278 | ||
279 | The PLT is a synthetic area, created by the linker. It exists in | |
280 | both executables and libraries. It is an array of stubs, one per | |
281 | imported function call. It looks like this: | |
282 | ||
283 | PLT[0]: | |
284 | str lr, [sp, #-4]! @push the return address (lr) | |
285 | ldr lr, [pc, #16] @load from 6 words ahead | |
286 | add lr, pc, lr @form an address for GOT[0] | |
287 | ldr pc, [lr, #8]! @jump to the contents of that addr | |
288 | ||
289 | The return address (lr) is pushed on the stack and used for | |
290 | calculations. The load on the second line loads the lr with | |
291 | &GOT[3] - . - 20. The addition on the third leaves: | |
292 | ||
293 | lr = (&GOT[3] - . - 20) + (. + 8) | |
294 | lr = (&GOT[3] - 12) | |
295 | lr = &GOT[0] | |
296 | ||
297 | On the fourth line, the pc and lr are both updated, so that: | |
298 | ||
299 | pc = GOT[2] | |
300 | lr = &GOT[0] + 8 | |
301 | = &GOT[2] | |
302 | ||
303 | NOTE: PLT[0] borrows an offset .word from PLT[1]. This is a little | |
304 | "tight", but allows us to keep all the PLT entries the same size. | |
305 | ||
306 | PLT[n+1]: | |
307 | ldr ip, [pc, #4] @load offset from gotoff | |
308 | add ip, pc, ip @add the offset to the pc | |
309 | ldr pc, [ip] @jump to that address | |
310 | gotoff: .word GOT[n+3] - . | |
311 | ||
312 | The load on the first line, gets an offset from the fourth word of | |
313 | the PLT entry. The add on the second line makes ip = &GOT[n+3], | |
314 | which contains either a pointer to PLT[0] (the fixup trampoline) or | |
315 | a pointer to the actual code. | |
316 | ||
317 | 3) In the GOT: | |
318 | ||
319 | The GOT contains helper pointers for both code (PLT) fixups and | |
320 | data fixups. The first 3 entries of the GOT are special. The next | |
321 | M entries (where M is the number of entries in the PLT) belong to | |
322 | the PLT fixups. The next D (all remaining) entries belong to | |
323 | various data fixups. The actual size of the GOT is 3 + M + D. | |
324 | ||
325 | The GOT is also a synthetic area, created by the linker. It exists | |
326 | in both executables and libraries. When the GOT is first | |
327 | initialized , all the GOT entries relating to PLT fixups are | |
328 | pointing to code back at PLT[0]. | |
329 | ||
330 | The special entries in the GOT are: | |
331 | ||
332 | GOT[0] = linked list pointer used by the dynamic loader | |
333 | GOT[1] = pointer to the reloc table for this module | |
334 | GOT[2] = pointer to the fixup/resolver code | |
335 | ||
336 | The first invocation of function call comes through and uses the | |
337 | fixup/resolver code. On the entry to the fixup/resolver code: | |
338 | ||
339 | ip = &GOT[n+3] | |
340 | lr = &GOT[2] | |
341 | stack[0] = return address (lr) of the function call | |
342 | [r0, r1, r2, r3] are still the arguments to the function call | |
343 | ||
344 | This is enough information for the fixup/resolver code to work | |
345 | with. Before the fixup/resolver code returns, it actually calls | |
346 | the requested function and repairs &GOT[n+3]. */ | |
347 | ||
a52e6aac SB |
348 | /* Find the minimal symbol named NAME, and return both the minsym |
349 | struct and its objfile. This probably ought to be in minsym.c, but | |
350 | everything there is trying to deal with things like C++ and | |
351 | SOFUN_ADDRESS_MAYBE_TURQUOISE, ... Since this is so simple, it may | |
352 | be considered too special-purpose for general consumption. */ | |
353 | ||
354 | static struct minimal_symbol * | |
355 | find_minsym_and_objfile (char *name, struct objfile **objfile_p) | |
356 | { | |
357 | struct objfile *objfile; | |
358 | ||
359 | ALL_OBJFILES (objfile) | |
360 | { | |
361 | struct minimal_symbol *msym; | |
362 | ||
363 | ALL_OBJFILE_MSYMBOLS (objfile, msym) | |
364 | { | |
365 | if (SYMBOL_NAME (msym) | |
366 | && STREQ (SYMBOL_NAME (msym), name)) | |
367 | { | |
368 | *objfile_p = objfile; | |
369 | return msym; | |
370 | } | |
371 | } | |
372 | } | |
373 | ||
374 | return 0; | |
375 | } | |
376 | ||
377 | ||
378 | static CORE_ADDR | |
379 | skip_hurd_resolver (CORE_ADDR pc) | |
380 | { | |
381 | /* The HURD dynamic linker is part of the GNU C library, so many | |
382 | GNU/Linux distributions use it. (All ELF versions, as far as I | |
383 | know.) An unresolved PLT entry points to "_dl_runtime_resolve", | |
384 | which calls "fixup" to patch the PLT, and then passes control to | |
385 | the function. | |
386 | ||
387 | We look for the symbol `_dl_runtime_resolve', and find `fixup' in | |
388 | the same objfile. If we are at the entry point of `fixup', then | |
389 | we set a breakpoint at the return address (at the top of the | |
390 | stack), and continue. | |
391 | ||
392 | It's kind of gross to do all these checks every time we're | |
393 | called, since they don't change once the executable has gotten | |
394 | started. But this is only a temporary hack --- upcoming versions | |
395 | of Linux will provide a portable, efficient interface for | |
396 | debugging programs that use shared libraries. */ | |
397 | ||
398 | struct objfile *objfile; | |
399 | struct minimal_symbol *resolver | |
400 | = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile); | |
401 | ||
402 | if (resolver) | |
403 | { | |
404 | struct minimal_symbol *fixup | |
405 | = lookup_minimal_symbol ("fixup", 0, objfile); | |
406 | ||
407 | if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc) | |
408 | return (SAVED_PC_AFTER_CALL (get_current_frame ())); | |
409 | } | |
410 | ||
411 | return 0; | |
412 | } | |
413 | ||
414 | /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c. | |
415 | This function: | |
416 | 1) decides whether a PLT has sent us into the linker to resolve | |
417 | a function reference, and | |
418 | 2) if so, tells us where to set a temporary breakpoint that will | |
419 | trigger when the dynamic linker is done. */ | |
420 | ||
f38e884d | 421 | CORE_ADDR |
a52e6aac | 422 | arm_linux_skip_solib_resolver (CORE_ADDR pc) |
f38e884d | 423 | { |
a52e6aac SB |
424 | CORE_ADDR result; |
425 | ||
426 | /* Plug in functions for other kinds of resolvers here. */ | |
427 | result = skip_hurd_resolver (pc); | |
428 | printf ("Result = 0x%08x\n"); | |
429 | if (result) | |
430 | return result; | |
431 | ||
432 | ||
f38e884d SB |
433 | return 0; |
434 | } | |
435 | ||
faf5f7ad SB |
436 | void |
437 | _initialize_arm_linux_tdep (void) | |
438 | { | |
439 | } |