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e7ee86a9 | 1 | /* Target-dependent code for Linux running on i386's, for GDB. |
4e052eda | 2 | Copyright 2000, 2001 Free Software Foundation, Inc. |
e7ee86a9 JB |
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" | |
22 | #include "gdbcore.h" | |
23 | #include "frame.h" | |
24 | #include "value.h" | |
4e052eda | 25 | #include "regcache.h" |
e7ee86a9 | 26 | |
bafda96e MS |
27 | /* For i386_linux_skip_solib_resolver. */ |
28 | #include "symtab.h" | |
29 | #include "symfile.h" | |
30 | #include "objfiles.h" | |
1a8629c7 | 31 | #include "solib-svr4.h" /* for struct link_map_offsets */ |
bafda96e | 32 | |
e7ee86a9 JB |
33 | \f |
34 | /* Recognizing signal handler frames. */ | |
35 | ||
36 | /* Linux has two flavors of signals. Normal signal handlers, and | |
37 | "realtime" (RT) signals. The RT signals can provide additional | |
38 | information to the signal handler if the SA_SIGINFO flag is set | |
39 | when establishing a signal handler using `sigaction'. It is not | |
40 | unlikely that future versions of Linux will support SA_SIGINFO for | |
41 | normal signals too. */ | |
42 | ||
43 | /* When the i386 Linux kernel calls a signal handler and the | |
44 | SA_RESTORER flag isn't set, the return address points to a bit of | |
45 | code on the stack. This function returns whether the PC appears to | |
46 | be within this bit of code. | |
47 | ||
48 | The instruction sequence for normal signals is | |
49 | pop %eax | |
50 | mov $0x77,%eax | |
51 | int $0x80 | |
52 | or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. | |
53 | ||
54 | Checking for the code sequence should be somewhat reliable, because | |
55 | the effect is to call the system call sigreturn. This is unlikely | |
56 | to occur anywhere other than a signal trampoline. | |
57 | ||
58 | It kind of sucks that we have to read memory from the process in | |
59 | order to identify a signal trampoline, but there doesn't seem to be | |
60 | any other way. The IN_SIGTRAMP macro in tm-linux.h arranges to | |
61 | only call us if no function name could be identified, which should | |
62 | be the case since the code is on the stack. | |
63 | ||
64 | Detection of signal trampolines for handlers that set the | |
65 | SA_RESTORER flag is in general not possible. Unfortunately this is | |
66 | what the GNU C Library has been doing for quite some time now. | |
67 | However, as of version 2.1.2, the GNU C Library uses signal | |
68 | trampolines (named __restore and __restore_rt) that are identical | |
69 | to the ones used by the kernel. Therefore, these trampolines are | |
70 | supported too. */ | |
71 | ||
72 | #define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ | |
73 | #define LINUX_SIGTRAMP_OFFSET0 (0) | |
74 | #define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ | |
75 | #define LINUX_SIGTRAMP_OFFSET1 (1) | |
76 | #define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ | |
77 | #define LINUX_SIGTRAMP_OFFSET2 (6) | |
78 | ||
79 | static const unsigned char linux_sigtramp_code[] = | |
80 | { | |
81 | LINUX_SIGTRAMP_INSN0, /* pop %eax */ | |
82 | LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ | |
83 | LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ | |
84 | }; | |
85 | ||
86 | #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) | |
87 | ||
88 | /* If PC is in a sigtramp routine, return the address of the start of | |
89 | the routine. Otherwise, return 0. */ | |
90 | ||
91 | static CORE_ADDR | |
92 | i386_linux_sigtramp_start (CORE_ADDR pc) | |
93 | { | |
94 | unsigned char buf[LINUX_SIGTRAMP_LEN]; | |
95 | ||
96 | /* We only recognize a signal trampoline if PC is at the start of | |
97 | one of the three instructions. We optimize for finding the PC at | |
98 | the start, as will be the case when the trampoline is not the | |
99 | first frame on the stack. We assume that in the case where the | |
100 | PC is not at the start of the instruction sequence, there will be | |
101 | a few trailing readable bytes on the stack. */ | |
102 | ||
103 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) | |
104 | return 0; | |
105 | ||
106 | if (buf[0] != LINUX_SIGTRAMP_INSN0) | |
107 | { | |
108 | int adjust; | |
109 | ||
110 | switch (buf[0]) | |
111 | { | |
112 | case LINUX_SIGTRAMP_INSN1: | |
113 | adjust = LINUX_SIGTRAMP_OFFSET1; | |
114 | break; | |
115 | case LINUX_SIGTRAMP_INSN2: | |
116 | adjust = LINUX_SIGTRAMP_OFFSET2; | |
117 | break; | |
118 | default: | |
119 | return 0; | |
120 | } | |
121 | ||
122 | pc -= adjust; | |
123 | ||
124 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) | |
125 | return 0; | |
126 | } | |
127 | ||
128 | if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) | |
129 | return 0; | |
130 | ||
131 | return pc; | |
132 | } | |
133 | ||
134 | /* This function does the same for RT signals. Here the instruction | |
135 | sequence is | |
136 | mov $0xad,%eax | |
137 | int $0x80 | |
138 | or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80. | |
139 | ||
140 | The effect is to call the system call rt_sigreturn. */ | |
141 | ||
142 | #define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */ | |
143 | #define LINUX_RT_SIGTRAMP_OFFSET0 (0) | |
144 | #define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */ | |
145 | #define LINUX_RT_SIGTRAMP_OFFSET1 (5) | |
146 | ||
147 | static const unsigned char linux_rt_sigtramp_code[] = | |
148 | { | |
149 | LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */ | |
150 | LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */ | |
151 | }; | |
152 | ||
153 | #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code) | |
154 | ||
155 | /* If PC is in a RT sigtramp routine, return the address of the start | |
156 | of the routine. Otherwise, return 0. */ | |
157 | ||
158 | static CORE_ADDR | |
159 | i386_linux_rt_sigtramp_start (CORE_ADDR pc) | |
160 | { | |
161 | unsigned char buf[LINUX_RT_SIGTRAMP_LEN]; | |
162 | ||
163 | /* We only recognize a signal trampoline if PC is at the start of | |
164 | one of the two instructions. We optimize for finding the PC at | |
165 | the start, as will be the case when the trampoline is not the | |
166 | first frame on the stack. We assume that in the case where the | |
167 | PC is not at the start of the instruction sequence, there will be | |
168 | a few trailing readable bytes on the stack. */ | |
169 | ||
170 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) | |
171 | return 0; | |
172 | ||
173 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN0) | |
174 | { | |
175 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN1) | |
176 | return 0; | |
177 | ||
178 | pc -= LINUX_RT_SIGTRAMP_OFFSET1; | |
179 | ||
180 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) | |
181 | return 0; | |
182 | } | |
183 | ||
184 | if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0) | |
185 | return 0; | |
186 | ||
187 | return pc; | |
188 | } | |
189 | ||
190 | /* Return whether PC is in a Linux sigtramp routine. */ | |
191 | ||
192 | int | |
193 | i386_linux_in_sigtramp (CORE_ADDR pc, char *name) | |
194 | { | |
195 | if (name) | |
196 | return STREQ ("__restore", name) || STREQ ("__restore_rt", name); | |
197 | ||
198 | return (i386_linux_sigtramp_start (pc) != 0 | |
199 | || i386_linux_rt_sigtramp_start (pc) != 0); | |
200 | } | |
201 | ||
202 | /* Assuming FRAME is for a Linux sigtramp routine, return the address | |
203 | of the associated sigcontext structure. */ | |
204 | ||
205 | CORE_ADDR | |
206 | i386_linux_sigcontext_addr (struct frame_info *frame) | |
207 | { | |
208 | CORE_ADDR pc; | |
209 | ||
210 | pc = i386_linux_sigtramp_start (frame->pc); | |
211 | if (pc) | |
212 | { | |
213 | CORE_ADDR sp; | |
214 | ||
215 | if (frame->next) | |
216 | /* If this isn't the top frame, the next frame must be for the | |
217 | signal handler itself. The sigcontext structure lives on | |
218 | the stack, right after the signum argument. */ | |
219 | return frame->next->frame + 12; | |
220 | ||
221 | /* This is the top frame. We'll have to find the address of the | |
222 | sigcontext structure by looking at the stack pointer. Keep | |
223 | in mind that the first instruction of the sigtramp code is | |
224 | "pop %eax". If the PC is at this instruction, adjust the | |
225 | returned value accordingly. */ | |
226 | sp = read_register (SP_REGNUM); | |
227 | if (pc == frame->pc) | |
228 | return sp + 4; | |
229 | return sp; | |
230 | } | |
231 | ||
232 | pc = i386_linux_rt_sigtramp_start (frame->pc); | |
233 | if (pc) | |
234 | { | |
235 | if (frame->next) | |
236 | /* If this isn't the top frame, the next frame must be for the | |
237 | signal handler itself. The sigcontext structure is part of | |
238 | the user context. A pointer to the user context is passed | |
239 | as the third argument to the signal handler. */ | |
240 | return read_memory_integer (frame->next->frame + 16, 4) + 20; | |
241 | ||
242 | /* This is the top frame. Again, use the stack pointer to find | |
243 | the address of the sigcontext structure. */ | |
244 | return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20; | |
245 | } | |
246 | ||
247 | error ("Couldn't recognize signal trampoline."); | |
248 | return 0; | |
249 | } | |
250 | ||
251 | /* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */ | |
252 | #define LINUX_SIGCONTEXT_PC_OFFSET (56) | |
253 | ||
254 | /* Assuming FRAME is for a Linux sigtramp routine, return the saved | |
255 | program counter. */ | |
256 | ||
257 | CORE_ADDR | |
258 | i386_linux_sigtramp_saved_pc (struct frame_info *frame) | |
259 | { | |
260 | CORE_ADDR addr; | |
261 | addr = i386_linux_sigcontext_addr (frame); | |
262 | return read_memory_integer (addr + LINUX_SIGCONTEXT_PC_OFFSET, 4); | |
263 | } | |
264 | ||
265 | /* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */ | |
266 | #define LINUX_SIGCONTEXT_SP_OFFSET (28) | |
267 | ||
268 | /* Assuming FRAME is for a Linux sigtramp routine, return the saved | |
269 | stack pointer. */ | |
270 | ||
271 | CORE_ADDR | |
272 | i386_linux_sigtramp_saved_sp (struct frame_info *frame) | |
273 | { | |
274 | CORE_ADDR addr; | |
275 | addr = i386_linux_sigcontext_addr (frame); | |
276 | return read_memory_integer (addr + LINUX_SIGCONTEXT_SP_OFFSET, 4); | |
277 | } | |
278 | ||
279 | /* Immediately after a function call, return the saved pc. */ | |
280 | ||
281 | CORE_ADDR | |
282 | i386_linux_saved_pc_after_call (struct frame_info *frame) | |
283 | { | |
284 | if (frame->signal_handler_caller) | |
285 | return i386_linux_sigtramp_saved_pc (frame); | |
286 | ||
287 | return read_memory_integer (read_register (SP_REGNUM), 4); | |
288 | } | |
bafda96e MS |
289 | |
290 | \f | |
291 | ||
292 | /* Calling functions in shared libraries. */ | |
293 | /* Find the minimal symbol named NAME, and return both the minsym | |
294 | struct and its objfile. This probably ought to be in minsym.c, but | |
295 | everything there is trying to deal with things like C++ and | |
296 | SOFUN_ADDRESS_MAYBE_TURQUOISE, ... Since this is so simple, it may | |
297 | be considered too special-purpose for general consumption. */ | |
298 | ||
299 | static struct minimal_symbol * | |
300 | find_minsym_and_objfile (char *name, struct objfile **objfile_p) | |
301 | { | |
302 | struct objfile *objfile; | |
303 | ||
304 | ALL_OBJFILES (objfile) | |
305 | { | |
306 | struct minimal_symbol *msym; | |
307 | ||
308 | ALL_OBJFILE_MSYMBOLS (objfile, msym) | |
309 | { | |
310 | if (SYMBOL_NAME (msym) | |
311 | && STREQ (SYMBOL_NAME (msym), name)) | |
312 | { | |
313 | *objfile_p = objfile; | |
314 | return msym; | |
315 | } | |
316 | } | |
317 | } | |
318 | ||
319 | return 0; | |
320 | } | |
321 | ||
322 | static CORE_ADDR | |
323 | skip_hurd_resolver (CORE_ADDR pc) | |
324 | { | |
325 | /* The HURD dynamic linker is part of the GNU C library, so many | |
326 | GNU/Linux distributions use it. (All ELF versions, as far as I | |
327 | know.) An unresolved PLT entry points to "_dl_runtime_resolve", | |
328 | which calls "fixup" to patch the PLT, and then passes control to | |
329 | the function. | |
330 | ||
331 | We look for the symbol `_dl_runtime_resolve', and find `fixup' in | |
332 | the same objfile. If we are at the entry point of `fixup', then | |
333 | we set a breakpoint at the return address (at the top of the | |
334 | stack), and continue. | |
335 | ||
336 | It's kind of gross to do all these checks every time we're | |
337 | called, since they don't change once the executable has gotten | |
338 | started. But this is only a temporary hack --- upcoming versions | |
339 | of Linux will provide a portable, efficient interface for | |
340 | debugging programs that use shared libraries. */ | |
341 | ||
342 | struct objfile *objfile; | |
343 | struct minimal_symbol *resolver | |
344 | = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile); | |
345 | ||
346 | if (resolver) | |
347 | { | |
348 | struct minimal_symbol *fixup | |
349 | = lookup_minimal_symbol ("fixup", 0, objfile); | |
350 | ||
351 | if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc) | |
352 | return (SAVED_PC_AFTER_CALL (get_current_frame ())); | |
353 | } | |
354 | ||
355 | return 0; | |
356 | } | |
357 | ||
358 | /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c. | |
359 | This function: | |
360 | 1) decides whether a PLT has sent us into the linker to resolve | |
361 | a function reference, and | |
362 | 2) if so, tells us where to set a temporary breakpoint that will | |
363 | trigger when the dynamic linker is done. */ | |
364 | ||
365 | CORE_ADDR | |
366 | i386_linux_skip_solib_resolver (CORE_ADDR pc) | |
367 | { | |
368 | CORE_ADDR result; | |
369 | ||
370 | /* Plug in functions for other kinds of resolvers here. */ | |
371 | result = skip_hurd_resolver (pc); | |
372 | if (result) | |
373 | return result; | |
374 | ||
375 | return 0; | |
376 | } | |
1a8629c7 MS |
377 | |
378 | /* Fetch (and possibly build) an appropriate link_map_offsets structure | |
379 | for native i386 linux targets using the struct offsets defined in | |
380 | link.h (but without actual reference to that file). | |
381 | ||
382 | This makes it possible to access i386-linux shared libraries from | |
383 | a gdb that was not built on an i386-linux host (for cross debugging). | |
384 | */ | |
385 | ||
386 | struct link_map_offsets * | |
387 | i386_linux_svr4_fetch_link_map_offsets (void) | |
388 | { | |
389 | static struct link_map_offsets lmo; | |
390 | static struct link_map_offsets *lmp = 0; | |
391 | ||
392 | if (lmp == 0) | |
393 | { | |
394 | lmp = &lmo; | |
395 | ||
396 | lmo.r_debug_size = 8; /* 20 not actual size but all we need */ | |
397 | ||
398 | lmo.r_map_offset = 4; | |
399 | lmo.r_map_size = 4; | |
400 | ||
401 | lmo.link_map_size = 20; /* 552 not actual size but all we need */ | |
402 | ||
403 | lmo.l_addr_offset = 0; | |
404 | lmo.l_addr_size = 4; | |
405 | ||
406 | lmo.l_name_offset = 4; | |
407 | lmo.l_name_size = 4; | |
408 | ||
409 | lmo.l_next_offset = 12; | |
410 | lmo.l_next_size = 4; | |
411 | ||
412 | lmo.l_prev_offset = 16; | |
413 | lmo.l_prev_size = 4; | |
414 | } | |
415 | ||
416 | return lmp; | |
417 | } | |
418 |