1 /* Target-dependent code for Linux running on i386's, for GDB.
2 Copyright 2000, 2001 Free Software Foundation, Inc.
4 This file is part of GDB.
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.
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.
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. */
27 /* For i386_linux_skip_solib_resolver. */
32 #include "solib-svr4.h" /* For struct link_map_offsets. */
35 /* Recognizing signal handler frames. */
37 /* Linux has two flavors of signals. Normal signal handlers, and
38 "realtime" (RT) signals. The RT signals can provide additional
39 information to the signal handler if the SA_SIGINFO flag is set
40 when establishing a signal handler using `sigaction'. It is not
41 unlikely that future versions of Linux will support SA_SIGINFO for
42 normal signals too. */
44 /* When the i386 Linux kernel calls a signal handler and the
45 SA_RESTORER flag isn't set, the return address points to a bit of
46 code on the stack. This function returns whether the PC appears to
47 be within this bit of code.
49 The instruction sequence for normal signals is
53 or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80.
55 Checking for the code sequence should be somewhat reliable, because
56 the effect is to call the system call sigreturn. This is unlikely
57 to occur anywhere other than a signal trampoline.
59 It kind of sucks that we have to read memory from the process in
60 order to identify a signal trampoline, but there doesn't seem to be
61 any other way. The IN_SIGTRAMP macro in tm-linux.h arranges to
62 only call us if no function name could be identified, which should
63 be the case since the code is on the stack.
65 Detection of signal trampolines for handlers that set the
66 SA_RESTORER flag is in general not possible. Unfortunately this is
67 what the GNU C Library has been doing for quite some time now.
68 However, as of version 2.1.2, the GNU C Library uses signal
69 trampolines (named __restore and __restore_rt) that are identical
70 to the ones used by the kernel. Therefore, these trampolines are
73 #define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */
74 #define LINUX_SIGTRAMP_OFFSET0 (0)
75 #define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */
76 #define LINUX_SIGTRAMP_OFFSET1 (1)
77 #define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */
78 #define LINUX_SIGTRAMP_OFFSET2 (6)
80 static const unsigned char linux_sigtramp_code
[] =
82 LINUX_SIGTRAMP_INSN0
, /* pop %eax */
83 LINUX_SIGTRAMP_INSN1
, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */
84 LINUX_SIGTRAMP_INSN2
, 0x80 /* int $0x80 */
87 #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code)
89 /* If PC is in a sigtramp routine, return the address of the start of
90 the routine. Otherwise, return 0. */
93 i386_linux_sigtramp_start (CORE_ADDR pc
)
95 unsigned char buf
[LINUX_SIGTRAMP_LEN
];
97 /* We only recognize a signal trampoline if PC is at the start of
98 one of the three instructions. We optimize for finding the PC at
99 the start, as will be the case when the trampoline is not the
100 first frame on the stack. We assume that in the case where the
101 PC is not at the start of the instruction sequence, there will be
102 a few trailing readable bytes on the stack. */
104 if (read_memory_nobpt (pc
, (char *) buf
, LINUX_SIGTRAMP_LEN
) != 0)
107 if (buf
[0] != LINUX_SIGTRAMP_INSN0
)
113 case LINUX_SIGTRAMP_INSN1
:
114 adjust
= LINUX_SIGTRAMP_OFFSET1
;
116 case LINUX_SIGTRAMP_INSN2
:
117 adjust
= LINUX_SIGTRAMP_OFFSET2
;
125 if (read_memory_nobpt (pc
, (char *) buf
, LINUX_SIGTRAMP_LEN
) != 0)
129 if (memcmp (buf
, linux_sigtramp_code
, LINUX_SIGTRAMP_LEN
) != 0)
135 /* This function does the same for RT signals. Here the instruction
139 or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80.
141 The effect is to call the system call rt_sigreturn. */
143 #define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */
144 #define LINUX_RT_SIGTRAMP_OFFSET0 (0)
145 #define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */
146 #define LINUX_RT_SIGTRAMP_OFFSET1 (5)
148 static const unsigned char linux_rt_sigtramp_code
[] =
150 LINUX_RT_SIGTRAMP_INSN0
, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */
151 LINUX_RT_SIGTRAMP_INSN1
, 0x80 /* int $0x80 */
154 #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code)
156 /* If PC is in a RT sigtramp routine, return the address of the start
157 of the routine. Otherwise, return 0. */
160 i386_linux_rt_sigtramp_start (CORE_ADDR pc
)
162 unsigned char buf
[LINUX_RT_SIGTRAMP_LEN
];
164 /* We only recognize a signal trampoline if PC is at the start of
165 one of the two instructions. We optimize for finding the PC at
166 the start, as will be the case when the trampoline is not the
167 first frame on the stack. We assume that in the case where the
168 PC is not at the start of the instruction sequence, there will be
169 a few trailing readable bytes on the stack. */
171 if (read_memory_nobpt (pc
, (char *) buf
, LINUX_RT_SIGTRAMP_LEN
) != 0)
174 if (buf
[0] != LINUX_RT_SIGTRAMP_INSN0
)
176 if (buf
[0] != LINUX_RT_SIGTRAMP_INSN1
)
179 pc
-= LINUX_RT_SIGTRAMP_OFFSET1
;
181 if (read_memory_nobpt (pc
, (char *) buf
, LINUX_RT_SIGTRAMP_LEN
) != 0)
185 if (memcmp (buf
, linux_rt_sigtramp_code
, LINUX_RT_SIGTRAMP_LEN
) != 0)
191 /* Return whether PC is in a Linux sigtramp routine. */
194 i386_linux_in_sigtramp (CORE_ADDR pc
, char *name
)
197 return STREQ ("__restore", name
) || STREQ ("__restore_rt", name
);
199 return (i386_linux_sigtramp_start (pc
) != 0
200 || i386_linux_rt_sigtramp_start (pc
) != 0);
203 /* Assuming FRAME is for a Linux sigtramp routine, return the address
204 of the associated sigcontext structure. */
207 i386_linux_sigcontext_addr (struct frame_info
*frame
)
211 pc
= i386_linux_sigtramp_start (frame
->pc
);
217 /* If this isn't the top frame, the next frame must be for the
218 signal handler itself. The sigcontext structure lives on
219 the stack, right after the signum argument. */
220 return frame
->next
->frame
+ 12;
222 /* This is the top frame. We'll have to find the address of the
223 sigcontext structure by looking at the stack pointer. Keep
224 in mind that the first instruction of the sigtramp code is
225 "pop %eax". If the PC is at this instruction, adjust the
226 returned value accordingly. */
227 sp
= read_register (SP_REGNUM
);
233 pc
= i386_linux_rt_sigtramp_start (frame
->pc
);
237 /* If this isn't the top frame, the next frame must be for the
238 signal handler itself. The sigcontext structure is part of
239 the user context. A pointer to the user context is passed
240 as the third argument to the signal handler. */
241 return read_memory_integer (frame
->next
->frame
+ 16, 4) + 20;
243 /* This is the top frame. Again, use the stack pointer to find
244 the address of the sigcontext structure. */
245 return read_memory_integer (read_register (SP_REGNUM
) + 8, 4) + 20;
248 error ("Couldn't recognize signal trampoline.");
252 /* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */
253 #define LINUX_SIGCONTEXT_PC_OFFSET (56)
255 /* Assuming FRAME is for a Linux sigtramp routine, return the saved
259 i386_linux_sigtramp_saved_pc (struct frame_info
*frame
)
262 addr
= i386_linux_sigcontext_addr (frame
);
263 return read_memory_integer (addr
+ LINUX_SIGCONTEXT_PC_OFFSET
, 4);
266 /* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */
267 #define LINUX_SIGCONTEXT_SP_OFFSET (28)
269 /* Assuming FRAME is for a Linux sigtramp routine, return the saved
273 i386_linux_sigtramp_saved_sp (struct frame_info
*frame
)
276 addr
= i386_linux_sigcontext_addr (frame
);
277 return read_memory_integer (addr
+ LINUX_SIGCONTEXT_SP_OFFSET
, 4);
280 /* Signal trampolines don't have a meaningful frame. As in
281 "i386/tm-i386.h", the frame pointer value we use is actually the
282 frame pointer of the calling frame -- that is, the frame which was
283 in progress when the signal trampoline was entered. GDB mostly
284 treats this frame pointer value as a magic cookie. We detect the
285 case of a signal trampoline by looking at the SIGNAL_HANDLER_CALLER
286 field, which is set based on IN_SIGTRAMP.
288 When a signal trampoline is invoked from a frameless function, we
289 essentially have two frameless functions in a row. In this case,
290 we use the same magic cookie for three frames in a row. We detect
291 this case by seeing whether the next frame has
292 SIGNAL_HANDLER_CALLER set, and, if it does, checking whether the
293 current frame is actually frameless. In this case, we need to get
294 the PC by looking at the SP register value stored in the signal
297 This should work in most cases except in horrible situations where
298 a signal occurs just as we enter a function but before the frame
301 #define FRAMELESS_SIGNAL(frame) \
302 ((frame)->next != NULL \
303 && (frame)->next->signal_handler_caller \
304 && frameless_look_for_prologue (frame))
307 i386_linux_frame_chain (struct frame_info
*frame
)
309 if (frame
->signal_handler_caller
|| FRAMELESS_SIGNAL (frame
))
312 if (! inside_entry_file (frame
->pc
))
313 return read_memory_unsigned_integer (frame
->frame
, 4);
318 /* Return the saved program counter for FRAME. */
321 i386_linux_frame_saved_pc (struct frame_info
*frame
)
323 if (frame
->signal_handler_caller
)
324 return i386_linux_sigtramp_saved_pc (frame
);
326 if (FRAMELESS_SIGNAL (frame
))
328 CORE_ADDR sp
= i386_linux_sigtramp_saved_sp (frame
->next
);
329 return read_memory_unsigned_integer (sp
, 4);
332 return read_memory_unsigned_integer (frame
->frame
+ 4, 4);
335 /* Immediately after a function call, return the saved pc. */
338 i386_linux_saved_pc_after_call (struct frame_info
*frame
)
340 if (frame
->signal_handler_caller
)
341 return i386_linux_sigtramp_saved_pc (frame
);
343 return read_memory_unsigned_integer (read_register (SP_REGNUM
), 4);
347 /* Calling functions in shared libraries. */
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. */
354 static struct minimal_symbol
*
355 find_minsym_and_objfile (char *name
, struct objfile
**objfile_p
)
357 struct objfile
*objfile
;
359 ALL_OBJFILES (objfile
)
361 struct minimal_symbol
*msym
;
363 ALL_OBJFILE_MSYMBOLS (objfile
, msym
)
365 if (SYMBOL_NAME (msym
)
366 && STREQ (SYMBOL_NAME (msym
), name
))
368 *objfile_p
= objfile
;
378 skip_hurd_resolver (CORE_ADDR pc
)
380 /* The HURD dynamic linker is part of the GNU C library, so many
381 GNU/Linux distributions use it. (All ELF versions, as far as I
382 know.) An unresolved PLT entry points to "_dl_runtime_resolve",
383 which calls "fixup" to patch the PLT, and then passes control to
386 We look for the symbol `_dl_runtime_resolve', and find `fixup' in
387 the same objfile. If we are at the entry point of `fixup', then
388 we set a breakpoint at the return address (at the top of the
389 stack), and continue.
391 It's kind of gross to do all these checks every time we're
392 called, since they don't change once the executable has gotten
393 started. But this is only a temporary hack --- upcoming versions
394 of Linux will provide a portable, efficient interface for
395 debugging programs that use shared libraries. */
397 struct objfile
*objfile
;
398 struct minimal_symbol
*resolver
399 = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile
);
403 struct minimal_symbol
*fixup
404 = lookup_minimal_symbol ("fixup", 0, objfile
);
406 if (fixup
&& SYMBOL_VALUE_ADDRESS (fixup
) == pc
)
407 return (SAVED_PC_AFTER_CALL (get_current_frame ()));
413 /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c.
415 1) decides whether a PLT has sent us into the linker to resolve
416 a function reference, and
417 2) if so, tells us where to set a temporary breakpoint that will
418 trigger when the dynamic linker is done. */
421 i386_linux_skip_solib_resolver (CORE_ADDR pc
)
425 /* Plug in functions for other kinds of resolvers here. */
426 result
= skip_hurd_resolver (pc
);
433 /* Fetch (and possibly build) an appropriate link_map_offsets
434 structure for native Linux/x86 targets using the struct offsets
435 defined in link.h (but without actual reference to that file).
437 This makes it possible to access Linux/x86 shared libraries from a
438 GDB that was not built on an Linux/x86 host (for cross debugging). */
440 struct link_map_offsets
*
441 i386_linux_svr4_fetch_link_map_offsets (void)
443 static struct link_map_offsets lmo
;
444 static struct link_map_offsets
*lmp
= NULL
;
450 lmo
.r_debug_size
= 8; /* The actual size is 20 bytes, but
451 this is all we need. */
452 lmo
.r_map_offset
= 4;
455 lmo
.link_map_size
= 20; /* The actual size is 552 bytes, but
456 this is all we need. */
457 lmo
.l_addr_offset
= 0;
460 lmo
.l_name_offset
= 4;
463 lmo
.l_next_offset
= 12;
466 lmo
.l_prev_offset
= 16;