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