Commit | Line | Data |
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ca557f44 AC |
1 | /* Target-dependent code for GNU/Linux running on i386's, for GDB. |
2 | ||
4be87837 | 3 | Copyright 2000, 2001, 2002, 2003 Free Software Foundation, Inc. |
e7ee86a9 JB |
4 | |
5 | This file is part of GDB. | |
6 | ||
7 | This program is free software; you can redistribute it and/or modify | |
8 | it under the terms of the GNU General Public License as published by | |
9 | the Free Software Foundation; either version 2 of the License, or | |
10 | (at your option) any later version. | |
11 | ||
12 | This program is distributed in the hope that it will be useful, | |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
15 | GNU General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU General Public License | |
18 | along with this program; if not, write to the Free Software | |
19 | Foundation, Inc., 59 Temple Place - Suite 330, | |
20 | Boston, MA 02111-1307, USA. */ | |
21 | ||
22 | #include "defs.h" | |
23 | #include "gdbcore.h" | |
24 | #include "frame.h" | |
25 | #include "value.h" | |
4e052eda | 26 | #include "regcache.h" |
6441c4a0 | 27 | #include "inferior.h" |
38c968cf | 28 | #include "reggroups.h" |
e7ee86a9 | 29 | |
bafda96e MS |
30 | /* For i386_linux_skip_solib_resolver. */ |
31 | #include "symtab.h" | |
32 | #include "symfile.h" | |
33 | #include "objfiles.h" | |
305d65ca MK |
34 | |
35 | #include "solib-svr4.h" /* For struct link_map_offsets. */ | |
bafda96e | 36 | |
4be87837 DJ |
37 | #include "osabi.h" |
38 | ||
8201327c MK |
39 | #include "i386-tdep.h" |
40 | #include "i386-linux-tdep.h" | |
41 | ||
6441c4a0 MK |
42 | /* Return the name of register REG. */ |
43 | ||
16775908 | 44 | static const char * |
6441c4a0 MK |
45 | i386_linux_register_name (int reg) |
46 | { | |
47 | /* Deal with the extra "orig_eax" pseudo register. */ | |
48 | if (reg == I386_LINUX_ORIG_EAX_REGNUM) | |
49 | return "orig_eax"; | |
50 | ||
51 | return i386_register_name (reg); | |
52 | } | |
38c968cf AC |
53 | |
54 | /* Return non-zero, when the register is in the corresponding register | |
55 | group. Put the LINUX_ORIG_EAX register in the system group. */ | |
56 | static int | |
57 | i386_linux_register_reggroup_p (struct gdbarch *gdbarch, int regnum, | |
58 | struct reggroup *group) | |
59 | { | |
60 | if (regnum == I386_LINUX_ORIG_EAX_REGNUM) | |
61 | return (group == system_reggroup | |
62 | || group == save_reggroup | |
63 | || group == restore_reggroup); | |
64 | return i386_register_reggroup_p (gdbarch, regnum, group); | |
65 | } | |
66 | ||
e7ee86a9 JB |
67 | \f |
68 | /* Recognizing signal handler frames. */ | |
69 | ||
ca557f44 | 70 | /* GNU/Linux has two flavors of signals. Normal signal handlers, and |
e7ee86a9 JB |
71 | "realtime" (RT) signals. The RT signals can provide additional |
72 | information to the signal handler if the SA_SIGINFO flag is set | |
73 | when establishing a signal handler using `sigaction'. It is not | |
ca557f44 AC |
74 | unlikely that future versions of GNU/Linux will support SA_SIGINFO |
75 | for normal signals too. */ | |
e7ee86a9 JB |
76 | |
77 | /* When the i386 Linux kernel calls a signal handler and the | |
78 | SA_RESTORER flag isn't set, the return address points to a bit of | |
79 | code on the stack. This function returns whether the PC appears to | |
80 | be within this bit of code. | |
81 | ||
82 | The instruction sequence for normal signals is | |
83 | pop %eax | |
84 | mov $0x77,%eax | |
85 | int $0x80 | |
86 | or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. | |
87 | ||
88 | Checking for the code sequence should be somewhat reliable, because | |
89 | the effect is to call the system call sigreturn. This is unlikely | |
90 | to occur anywhere other than a signal trampoline. | |
91 | ||
92 | It kind of sucks that we have to read memory from the process in | |
93 | order to identify a signal trampoline, but there doesn't seem to be | |
d7bd68ca | 94 | any other way. The PC_IN_SIGTRAMP macro in tm-linux.h arranges to |
e7ee86a9 JB |
95 | only call us if no function name could be identified, which should |
96 | be the case since the code is on the stack. | |
97 | ||
98 | Detection of signal trampolines for handlers that set the | |
99 | SA_RESTORER flag is in general not possible. Unfortunately this is | |
100 | what the GNU C Library has been doing for quite some time now. | |
101 | However, as of version 2.1.2, the GNU C Library uses signal | |
102 | trampolines (named __restore and __restore_rt) that are identical | |
103 | to the ones used by the kernel. Therefore, these trampolines are | |
104 | supported too. */ | |
105 | ||
106 | #define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ | |
107 | #define LINUX_SIGTRAMP_OFFSET0 (0) | |
108 | #define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ | |
109 | #define LINUX_SIGTRAMP_OFFSET1 (1) | |
110 | #define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ | |
111 | #define LINUX_SIGTRAMP_OFFSET2 (6) | |
112 | ||
113 | static const unsigned char linux_sigtramp_code[] = | |
114 | { | |
115 | LINUX_SIGTRAMP_INSN0, /* pop %eax */ | |
116 | LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ | |
117 | LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ | |
118 | }; | |
119 | ||
120 | #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) | |
121 | ||
122 | /* If PC is in a sigtramp routine, return the address of the start of | |
123 | the routine. Otherwise, return 0. */ | |
124 | ||
125 | static CORE_ADDR | |
126 | i386_linux_sigtramp_start (CORE_ADDR pc) | |
127 | { | |
128 | unsigned char buf[LINUX_SIGTRAMP_LEN]; | |
129 | ||
130 | /* We only recognize a signal trampoline if PC is at the start of | |
131 | one of the three instructions. We optimize for finding the PC at | |
132 | the start, as will be the case when the trampoline is not the | |
133 | first frame on the stack. We assume that in the case where the | |
134 | PC is not at the start of the instruction sequence, there will be | |
135 | a few trailing readable bytes on the stack. */ | |
136 | ||
137 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) | |
138 | return 0; | |
139 | ||
140 | if (buf[0] != LINUX_SIGTRAMP_INSN0) | |
141 | { | |
142 | int adjust; | |
143 | ||
144 | switch (buf[0]) | |
145 | { | |
146 | case LINUX_SIGTRAMP_INSN1: | |
147 | adjust = LINUX_SIGTRAMP_OFFSET1; | |
148 | break; | |
149 | case LINUX_SIGTRAMP_INSN2: | |
150 | adjust = LINUX_SIGTRAMP_OFFSET2; | |
151 | break; | |
152 | default: | |
153 | return 0; | |
154 | } | |
155 | ||
156 | pc -= adjust; | |
157 | ||
158 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) | |
159 | return 0; | |
160 | } | |
161 | ||
162 | if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) | |
163 | return 0; | |
164 | ||
165 | return pc; | |
166 | } | |
167 | ||
168 | /* This function does the same for RT signals. Here the instruction | |
169 | sequence is | |
170 | mov $0xad,%eax | |
171 | int $0x80 | |
172 | or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80. | |
173 | ||
174 | The effect is to call the system call rt_sigreturn. */ | |
175 | ||
176 | #define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */ | |
177 | #define LINUX_RT_SIGTRAMP_OFFSET0 (0) | |
178 | #define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */ | |
179 | #define LINUX_RT_SIGTRAMP_OFFSET1 (5) | |
180 | ||
181 | static const unsigned char linux_rt_sigtramp_code[] = | |
182 | { | |
183 | LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */ | |
184 | LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */ | |
185 | }; | |
186 | ||
187 | #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code) | |
188 | ||
189 | /* If PC is in a RT sigtramp routine, return the address of the start | |
190 | of the routine. Otherwise, return 0. */ | |
191 | ||
192 | static CORE_ADDR | |
193 | i386_linux_rt_sigtramp_start (CORE_ADDR pc) | |
194 | { | |
195 | unsigned char buf[LINUX_RT_SIGTRAMP_LEN]; | |
196 | ||
197 | /* We only recognize a signal trampoline if PC is at the start of | |
198 | one of the two instructions. We optimize for finding the PC at | |
199 | the start, as will be the case when the trampoline is not the | |
200 | first frame on the stack. We assume that in the case where the | |
201 | PC is not at the start of the instruction sequence, there will be | |
202 | a few trailing readable bytes on the stack. */ | |
203 | ||
204 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) | |
205 | return 0; | |
206 | ||
207 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN0) | |
208 | { | |
209 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN1) | |
210 | return 0; | |
211 | ||
212 | pc -= LINUX_RT_SIGTRAMP_OFFSET1; | |
213 | ||
214 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) | |
215 | return 0; | |
216 | } | |
217 | ||
218 | if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0) | |
219 | return 0; | |
220 | ||
221 | return pc; | |
222 | } | |
223 | ||
ca557f44 | 224 | /* Return whether PC is in a GNU/Linux sigtramp routine. */ |
e7ee86a9 | 225 | |
8201327c MK |
226 | static int |
227 | i386_linux_pc_in_sigtramp (CORE_ADDR pc, char *name) | |
e7ee86a9 | 228 | { |
ef17e74b DJ |
229 | /* If we have NAME, we can optimize the search. The trampolines are |
230 | named __restore and __restore_rt. However, they aren't dynamically | |
231 | exported from the shared C library, so the trampoline may appear to | |
232 | be part of the preceding function. This should always be sigaction, | |
233 | __sigaction, or __libc_sigaction (all aliases to the same function). */ | |
234 | if (name == NULL || strstr (name, "sigaction") != NULL) | |
235 | return (i386_linux_sigtramp_start (pc) != 0 | |
236 | || i386_linux_rt_sigtramp_start (pc) != 0); | |
237 | ||
238 | return (strcmp ("__restore", name) == 0 | |
239 | || strcmp ("__restore_rt", name) == 0); | |
e7ee86a9 JB |
240 | } |
241 | ||
ca557f44 AC |
242 | /* Assuming FRAME is for a GNU/Linux sigtramp routine, return the |
243 | address of the associated sigcontext structure. */ | |
e7ee86a9 | 244 | |
b7d15bf7 | 245 | static CORE_ADDR |
e7ee86a9 JB |
246 | i386_linux_sigcontext_addr (struct frame_info *frame) |
247 | { | |
248 | CORE_ADDR pc; | |
249 | ||
250 | pc = i386_linux_sigtramp_start (frame->pc); | |
251 | if (pc) | |
252 | { | |
253 | CORE_ADDR sp; | |
254 | ||
255 | if (frame->next) | |
256 | /* If this isn't the top frame, the next frame must be for the | |
257 | signal handler itself. The sigcontext structure lives on | |
258 | the stack, right after the signum argument. */ | |
259 | return frame->next->frame + 12; | |
260 | ||
261 | /* This is the top frame. We'll have to find the address of the | |
262 | sigcontext structure by looking at the stack pointer. Keep | |
263 | in mind that the first instruction of the sigtramp code is | |
264 | "pop %eax". If the PC is at this instruction, adjust the | |
265 | returned value accordingly. */ | |
266 | sp = read_register (SP_REGNUM); | |
267 | if (pc == frame->pc) | |
268 | return sp + 4; | |
269 | return sp; | |
270 | } | |
271 | ||
272 | pc = i386_linux_rt_sigtramp_start (frame->pc); | |
273 | if (pc) | |
274 | { | |
275 | if (frame->next) | |
276 | /* If this isn't the top frame, the next frame must be for the | |
277 | signal handler itself. The sigcontext structure is part of | |
278 | the user context. A pointer to the user context is passed | |
279 | as the third argument to the signal handler. */ | |
280 | return read_memory_integer (frame->next->frame + 16, 4) + 20; | |
281 | ||
282 | /* This is the top frame. Again, use the stack pointer to find | |
283 | the address of the sigcontext structure. */ | |
284 | return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20; | |
285 | } | |
286 | ||
287 | error ("Couldn't recognize signal trampoline."); | |
288 | return 0; | |
289 | } | |
290 | ||
6441c4a0 MK |
291 | /* Set the program counter for process PTID to PC. */ |
292 | ||
8201327c | 293 | static void |
6441c4a0 MK |
294 | i386_linux_write_pc (CORE_ADDR pc, ptid_t ptid) |
295 | { | |
296 | write_register_pid (PC_REGNUM, pc, ptid); | |
297 | ||
298 | /* We must be careful with modifying the program counter. If we | |
299 | just interrupted a system call, the kernel might try to restart | |
300 | it when we resume the inferior. On restarting the system call, | |
301 | the kernel will try backing up the program counter even though it | |
302 | no longer points at the system call. This typically results in a | |
303 | SIGSEGV or SIGILL. We can prevent this by writing `-1' in the | |
304 | "orig_eax" pseudo-register. | |
305 | ||
306 | Note that "orig_eax" is saved when setting up a dummy call frame. | |
307 | This means that it is properly restored when that frame is | |
308 | popped, and that the interrupted system call will be restarted | |
309 | when we resume the inferior on return from a function call from | |
310 | within GDB. In all other cases the system call will not be | |
311 | restarted. */ | |
312 | write_register_pid (I386_LINUX_ORIG_EAX_REGNUM, -1, ptid); | |
313 | } | |
314 | \f | |
bafda96e | 315 | /* Calling functions in shared libraries. */ |
6441c4a0 | 316 | |
bafda96e MS |
317 | /* Find the minimal symbol named NAME, and return both the minsym |
318 | struct and its objfile. This probably ought to be in minsym.c, but | |
319 | everything there is trying to deal with things like C++ and | |
320 | SOFUN_ADDRESS_MAYBE_TURQUOISE, ... Since this is so simple, it may | |
321 | be considered too special-purpose for general consumption. */ | |
322 | ||
323 | static struct minimal_symbol * | |
324 | find_minsym_and_objfile (char *name, struct objfile **objfile_p) | |
325 | { | |
326 | struct objfile *objfile; | |
327 | ||
328 | ALL_OBJFILES (objfile) | |
329 | { | |
330 | struct minimal_symbol *msym; | |
331 | ||
332 | ALL_OBJFILE_MSYMBOLS (objfile, msym) | |
333 | { | |
334 | if (SYMBOL_NAME (msym) | |
335 | && STREQ (SYMBOL_NAME (msym), name)) | |
336 | { | |
337 | *objfile_p = objfile; | |
338 | return msym; | |
339 | } | |
340 | } | |
341 | } | |
342 | ||
343 | return 0; | |
344 | } | |
345 | ||
346 | static CORE_ADDR | |
347 | skip_hurd_resolver (CORE_ADDR pc) | |
348 | { | |
349 | /* The HURD dynamic linker is part of the GNU C library, so many | |
350 | GNU/Linux distributions use it. (All ELF versions, as far as I | |
351 | know.) An unresolved PLT entry points to "_dl_runtime_resolve", | |
352 | which calls "fixup" to patch the PLT, and then passes control to | |
353 | the function. | |
354 | ||
355 | We look for the symbol `_dl_runtime_resolve', and find `fixup' in | |
356 | the same objfile. If we are at the entry point of `fixup', then | |
357 | we set a breakpoint at the return address (at the top of the | |
358 | stack), and continue. | |
359 | ||
360 | It's kind of gross to do all these checks every time we're | |
361 | called, since they don't change once the executable has gotten | |
362 | started. But this is only a temporary hack --- upcoming versions | |
ca557f44 | 363 | of GNU/Linux will provide a portable, efficient interface for |
bafda96e MS |
364 | debugging programs that use shared libraries. */ |
365 | ||
366 | struct objfile *objfile; | |
367 | struct minimal_symbol *resolver | |
368 | = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile); | |
369 | ||
370 | if (resolver) | |
371 | { | |
372 | struct minimal_symbol *fixup | |
9b27852e | 373 | = lookup_minimal_symbol ("fixup", NULL, objfile); |
bafda96e MS |
374 | |
375 | if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc) | |
376 | return (SAVED_PC_AFTER_CALL (get_current_frame ())); | |
377 | } | |
378 | ||
379 | return 0; | |
380 | } | |
381 | ||
382 | /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c. | |
383 | This function: | |
384 | 1) decides whether a PLT has sent us into the linker to resolve | |
385 | a function reference, and | |
386 | 2) if so, tells us where to set a temporary breakpoint that will | |
387 | trigger when the dynamic linker is done. */ | |
388 | ||
389 | CORE_ADDR | |
390 | i386_linux_skip_solib_resolver (CORE_ADDR pc) | |
391 | { | |
392 | CORE_ADDR result; | |
393 | ||
394 | /* Plug in functions for other kinds of resolvers here. */ | |
395 | result = skip_hurd_resolver (pc); | |
396 | if (result) | |
397 | return result; | |
398 | ||
399 | return 0; | |
400 | } | |
1a8629c7 | 401 | |
305d65ca | 402 | /* Fetch (and possibly build) an appropriate link_map_offsets |
ca557f44 | 403 | structure for native GNU/Linux x86 targets using the struct offsets |
305d65ca | 404 | defined in link.h (but without actual reference to that file). |
1a8629c7 | 405 | |
ca557f44 AC |
406 | This makes it possible to access GNU/Linux x86 shared libraries |
407 | from a GDB that was not built on an GNU/Linux x86 host (for cross | |
408 | debugging). */ | |
1a8629c7 | 409 | |
8201327c | 410 | static struct link_map_offsets * |
1a8629c7 MS |
411 | i386_linux_svr4_fetch_link_map_offsets (void) |
412 | { | |
413 | static struct link_map_offsets lmo; | |
305d65ca | 414 | static struct link_map_offsets *lmp = NULL; |
1a8629c7 | 415 | |
305d65ca | 416 | if (lmp == NULL) |
1a8629c7 MS |
417 | { |
418 | lmp = &lmo; | |
419 | ||
305d65ca MK |
420 | lmo.r_debug_size = 8; /* The actual size is 20 bytes, but |
421 | this is all we need. */ | |
1a8629c7 MS |
422 | lmo.r_map_offset = 4; |
423 | lmo.r_map_size = 4; | |
424 | ||
305d65ca MK |
425 | lmo.link_map_size = 20; /* The actual size is 552 bytes, but |
426 | this is all we need. */ | |
1a8629c7 MS |
427 | lmo.l_addr_offset = 0; |
428 | lmo.l_addr_size = 4; | |
429 | ||
430 | lmo.l_name_offset = 4; | |
431 | lmo.l_name_size = 4; | |
432 | ||
433 | lmo.l_next_offset = 12; | |
434 | lmo.l_next_size = 4; | |
435 | ||
436 | lmo.l_prev_offset = 16; | |
437 | lmo.l_prev_size = 4; | |
438 | } | |
439 | ||
305d65ca | 440 | return lmp; |
1a8629c7 | 441 | } |
8201327c MK |
442 | \f |
443 | ||
444 | static void | |
445 | i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch) | |
446 | { | |
447 | struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch); | |
448 | ||
449 | /* GNU/Linux uses ELF. */ | |
450 | i386_elf_init_abi (info, gdbarch); | |
451 | ||
452 | /* We support the SSE registers on GNU/Linux. */ | |
453 | tdep->num_xmm_regs = I386_NUM_XREGS - 1; | |
454 | /* set_gdbarch_num_regs (gdbarch, I386_SSE_NUM_REGS); */ | |
455 | ||
456 | /* Since we have the extra "orig_eax" register on GNU/Linux, we have | |
457 | to adjust a few things. */ | |
458 | ||
459 | set_gdbarch_write_pc (gdbarch, i386_linux_write_pc); | |
460 | set_gdbarch_num_regs (gdbarch, I386_SSE_NUM_REGS + 1); | |
461 | set_gdbarch_register_name (gdbarch, i386_linux_register_name); | |
38c968cf | 462 | set_gdbarch_register_reggroup_p (gdbarch, i386_linux_register_reggroup_p); |
8201327c | 463 | set_gdbarch_register_bytes (gdbarch, I386_SSE_SIZEOF_REGS + 4); |
8201327c MK |
464 | |
465 | tdep->jb_pc_offset = 20; /* From <bits/setjmp.h>. */ | |
466 | ||
b7d15bf7 MK |
467 | tdep->sigcontext_addr = i386_linux_sigcontext_addr; |
468 | tdep->sc_pc_offset = 14 * 4; /* From <asm/sigcontext.h>. */ | |
469 | tdep->sc_sp_offset = 7 * 4; | |
8201327c | 470 | |
b7d15bf7 MK |
471 | /* When the i386 Linux kernel calls a signal handler, the return |
472 | address points to a bit of code on the stack. This function is | |
473 | used to identify this bit of code as a signal trampoline in order | |
474 | to support backtracing through calls to signal handlers. */ | |
8201327c | 475 | set_gdbarch_pc_in_sigtramp (gdbarch, i386_linux_pc_in_sigtramp); |
8201327c MK |
476 | |
477 | set_solib_svr4_fetch_link_map_offsets (gdbarch, | |
478 | i386_linux_svr4_fetch_link_map_offsets); | |
479 | } | |
480 | ||
481 | /* Provide a prototype to silence -Wmissing-prototypes. */ | |
482 | extern void _initialize_i386_linux_tdep (void); | |
483 | ||
484 | void | |
485 | _initialize_i386_linux_tdep (void) | |
486 | { | |
05816f70 | 487 | gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_LINUX, |
8201327c MK |
488 | i386_linux_init_abi); |
489 | } |