1 /* Target-dependent code for GNU/Linux running on i386's, for GDB.
3 Copyright 2000, 2001, 2002 Free Software Foundation, Inc.
5 This file is part of GDB.
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.
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.
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. */
29 /* For i386_linux_skip_solib_resolver. */
34 #include "solib-svr4.h" /* For struct link_map_offsets. */
36 #include "i386-tdep.h"
37 #include "i386-linux-tdep.h"
39 /* Return the name of register REG. */
42 i386_linux_register_name (int reg)
44 /* Deal with the extra "orig_eax" pseudo register. */
45 if (reg == I386_LINUX_ORIG_EAX_REGNUM)
48 return i386_register_name (reg);
51 /* Recognizing signal handler frames. */
53 /* GNU/Linux has two flavors of signals. Normal signal handlers, and
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
57 unlikely that future versions of GNU/Linux will support SA_SIGINFO
58 for normal signals too. */
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.
65 The instruction sequence for normal signals is
69 or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80.
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.
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
77 any other way. The PC_IN_SIGTRAMP macro in tm-linux.h arranges to
78 only call us if no function name could be identified, which should
79 be the case since the code is on the stack.
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
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)
96 static const unsigned char linux_sigtramp_code[] =
98 LINUX_SIGTRAMP_INSN0, /* pop %eax */
99 LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */
100 LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */
103 #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code)
105 /* If PC is in a sigtramp routine, return the address of the start of
106 the routine. Otherwise, return 0. */
109 i386_linux_sigtramp_start (CORE_ADDR pc)
111 unsigned char buf[LINUX_SIGTRAMP_LEN];
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. */
120 if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0)
123 if (buf[0] != LINUX_SIGTRAMP_INSN0)
129 case LINUX_SIGTRAMP_INSN1:
130 adjust = LINUX_SIGTRAMP_OFFSET1;
132 case LINUX_SIGTRAMP_INSN2:
133 adjust = LINUX_SIGTRAMP_OFFSET2;
141 if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0)
145 if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0)
151 /* This function does the same for RT signals. Here the instruction
155 or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80.
157 The effect is to call the system call rt_sigreturn. */
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)
164 static const unsigned char linux_rt_sigtramp_code[] =
166 LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */
167 LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */
170 #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code)
172 /* If PC is in a RT sigtramp routine, return the address of the start
173 of the routine. Otherwise, return 0. */
176 i386_linux_rt_sigtramp_start (CORE_ADDR pc)
178 unsigned char buf[LINUX_RT_SIGTRAMP_LEN];
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. */
187 if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0)
190 if (buf[0] != LINUX_RT_SIGTRAMP_INSN0)
192 if (buf[0] != LINUX_RT_SIGTRAMP_INSN1)
195 pc -= LINUX_RT_SIGTRAMP_OFFSET1;
197 if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0)
201 if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0)
207 /* Return whether PC is in a GNU/Linux sigtramp routine. */
210 i386_linux_pc_in_sigtramp (CORE_ADDR pc, char *name)
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);
221 return (strcmp ("__restore", name) == 0
222 || strcmp ("__restore_rt", name) == 0);
225 /* Assuming FRAME is for a GNU/Linux sigtramp routine, return the
226 address of the associated sigcontext structure. */
229 i386_linux_sigcontext_addr (struct frame_info *frame)
233 pc = i386_linux_sigtramp_start (frame->pc);
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;
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);
255 pc = i386_linux_rt_sigtramp_start (frame->pc);
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;
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;
270 error ("Couldn't recognize signal trampoline.");
274 /* Set the program counter for process PTID to PC. */
277 i386_linux_write_pc (CORE_ADDR pc, ptid_t ptid)
279 write_register_pid (PC_REGNUM, pc, ptid);
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.
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
295 write_register_pid (I386_LINUX_ORIG_EAX_REGNUM, -1, ptid);
298 /* Calling functions in shared libraries. */
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. */
306 static struct minimal_symbol *
307 find_minsym_and_objfile (char *name, struct objfile **objfile_p)
309 struct objfile *objfile;
311 ALL_OBJFILES (objfile)
313 struct minimal_symbol *msym;
315 ALL_OBJFILE_MSYMBOLS (objfile, msym)
317 if (SYMBOL_NAME (msym)
318 && STREQ (SYMBOL_NAME (msym), name))
320 *objfile_p = objfile;
330 skip_hurd_resolver (CORE_ADDR pc)
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
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.
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
346 of GNU/Linux will provide a portable, efficient interface for
347 debugging programs that use shared libraries. */
349 struct objfile *objfile;
350 struct minimal_symbol *resolver
351 = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile);
355 struct minimal_symbol *fixup
356 = lookup_minimal_symbol ("fixup", NULL, objfile);
358 if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc)
359 return (SAVED_PC_AFTER_CALL (get_current_frame ()));
365 /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c.
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. */
373 i386_linux_skip_solib_resolver (CORE_ADDR pc)
377 /* Plug in functions for other kinds of resolvers here. */
378 result = skip_hurd_resolver (pc);
385 /* Fetch (and possibly build) an appropriate link_map_offsets
386 structure for native GNU/Linux x86 targets using the struct offsets
387 defined in link.h (but without actual reference to that file).
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
393 static struct link_map_offsets *
394 i386_linux_svr4_fetch_link_map_offsets (void)
396 static struct link_map_offsets lmo;
397 static struct link_map_offsets *lmp = NULL;
403 lmo.r_debug_size = 8; /* The actual size is 20 bytes, but
404 this is all we need. */
405 lmo.r_map_offset = 4;
408 lmo.link_map_size = 20; /* The actual size is 552 bytes, but
409 this is all we need. */
410 lmo.l_addr_offset = 0;
413 lmo.l_name_offset = 4;
416 lmo.l_next_offset = 12;
419 lmo.l_prev_offset = 16;
428 i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
430 struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
432 /* GNU/Linux uses ELF. */
433 i386_elf_init_abi (info, gdbarch);
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); */
439 /* Since we have the extra "orig_eax" register on GNU/Linux, we have
440 to adjust a few things. */
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);
447 tdep->jb_pc_offset = 20; /* From <bits/setjmp.h>. */
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;
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. */
457 set_gdbarch_pc_in_sigtramp (gdbarch, i386_linux_pc_in_sigtramp);
459 set_solib_svr4_fetch_link_map_offsets (gdbarch,
460 i386_linux_svr4_fetch_link_map_offsets);
463 /* Provide a prototype to silence -Wmissing-prototypes. */
464 extern void _initialize_i386_linux_tdep (void);
467 _initialize_i386_linux_tdep (void)
469 gdbarch_register_osabi (bfd_arch_i386, GDB_OSABI_LINUX,
470 i386_linux_init_abi);