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