gdb/i386-linux-tdep.c

   1 /* Target-dependent code for GNU/Linux i386.
   2
   3    Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005
   4    Free Software Foundation, Inc.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 2 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 51 Franklin Street, Fifth Floor,
  21    Boston, MA 02110-1301, USA.  */
  22
  23 #include "defs.h"
  24 #include "gdbcore.h"
  25 #include "frame.h"
  26 #include "value.h"
  27 #include "regcache.h"
  28 #include "inferior.h"
  29 #include "osabi.h"
  30 #include "reggroups.h"
  31 #include "dwarf2-frame.h"
  32 #include "gdb_string.h"
  33
  34 #include "i386-tdep.h"
  35 #include "i386-linux-tdep.h"
  36 #include "glibc-tdep.h"
  37 #include "solib-svr4.h"
  38
  39 /* Return the name of register REG.  */
  40
  41 static const char *
  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 }
  50
  51 /* Return non-zero, when the register is in the corresponding register
  52    group.  Put the LINUX_ORIG_EAX register in the system group.  */
  53 static int
  54 i386_linux_register_reggroup_p (struct gdbarch *gdbarch, int regnum,
  55                                 struct reggroup *group)
  56 {
  57   if (regnum == I386_LINUX_ORIG_EAX_REGNUM)
  58     return (group == system_reggroup
  59             || group == save_reggroup
  60             || group == restore_reggroup);
  61   return i386_register_reggroup_p (gdbarch, regnum, group);
  62 }
  63
  64 \f
  65 /* Recognizing signal handler frames.  */
  66
  67 /* GNU/Linux has two flavors of signals.  Normal signal handlers, and
  68    "realtime" (RT) signals.  The RT signals can provide additional
  69    information to the signal handler if the SA_SIGINFO flag is set
  70    when establishing a signal handler using `sigaction'.  It is not
  71    unlikely that future versions of GNU/Linux will support SA_SIGINFO
  72    for normal signals too.  */
  73
  74 /* When the i386 Linux kernel calls a signal handler and the
  75    SA_RESTORER flag isn't set, the return address points to a bit of
  76    code on the stack.  This function returns whether the PC appears to
  77    be within this bit of code.
  78
  79    The instruction sequence for normal signals is
  80        pop    %eax
  81        mov    $0x77, %eax
  82        int    $0x80
  83    or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80.
  84
  85    Checking for the code sequence should be somewhat reliable, because
  86    the effect is to call the system call sigreturn.  This is unlikely
  87    to occur anywhere other than in a signal trampoline.
  88
  89    It kind of sucks that we have to read memory from the process in
  90    order to identify a signal trampoline, but there doesn't seem to be
  91    any other way.  Therefore we only do the memory reads if no
  92    function name could be identified, which should be the case since
  93    the code is on the stack.
  94
  95    Detection of signal trampolines for handlers that set the
  96    SA_RESTORER flag is in general not possible.  Unfortunately this is
  97    what the GNU C Library has been doing for quite some time now.
  98    However, as of version 2.1.2, the GNU C Library uses signal
  99    trampolines (named __restore and __restore_rt) that are identical
 100    to the ones used by the kernel.  Therefore, these trampolines are
 101    supported too.  */
 102
 103 #define LINUX_SIGTRAMP_INSN0    0x58    /* pop %eax */
 104 #define LINUX_SIGTRAMP_OFFSET0  0
 105 #define LINUX_SIGTRAMP_INSN1    0xb8    /* mov $NNNN, %eax */
 106 #define LINUX_SIGTRAMP_OFFSET1  1
 107 #define LINUX_SIGTRAMP_INSN2    0xcd    /* int */
 108 #define LINUX_SIGTRAMP_OFFSET2  6
 109
 110 static const gdb_byte linux_sigtramp_code[] =
 111 {
 112   LINUX_SIGTRAMP_INSN0,                                 /* pop %eax */
 113   LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00,         /* mov $0x77, %eax */
 114   LINUX_SIGTRAMP_INSN2, 0x80                            /* int $0x80 */
 115 };
 116
 117 #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code)
 118
 119 /* If NEXT_FRAME unwinds into a sigtramp routine, return the address
 120    of the start of the routine.  Otherwise, return 0.  */
 121
 122 static CORE_ADDR
 123 i386_linux_sigtramp_start (struct frame_info *next_frame)
 124 {
 125   CORE_ADDR pc = frame_pc_unwind (next_frame);
 126   gdb_byte buf[LINUX_SIGTRAMP_LEN];
 127
 128   /* We only recognize a signal trampoline if PC is at the start of
 129      one of the three instructions.  We optimize for finding the PC at
 130      the start, as will be the case when the trampoline is not the
 131      first frame on the stack.  We assume that in the case where the
 132      PC is not at the start of the instruction sequence, there will be
 133      a few trailing readable bytes on the stack.  */
 134
 135   if (!safe_frame_unwind_memory (next_frame, pc, buf, LINUX_SIGTRAMP_LEN))
 136     return 0;
 137
 138   if (buf[0] != LINUX_SIGTRAMP_INSN0)
 139     {
 140       int adjust;
 141
 142       switch (buf[0])
 143         {
 144         case LINUX_SIGTRAMP_INSN1:
 145           adjust = LINUX_SIGTRAMP_OFFSET1;
 146           break;
 147         case LINUX_SIGTRAMP_INSN2:
 148           adjust = LINUX_SIGTRAMP_OFFSET2;
 149           break;
 150         default:
 151           return 0;
 152         }
 153
 154       pc -= adjust;
 155
 156       if (!safe_frame_unwind_memory (next_frame, pc, buf, LINUX_SIGTRAMP_LEN))
 157         return 0;
 158     }
 159
 160   if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0)
 161     return 0;
 162
 163   return pc;
 164 }
 165
 166 /* This function does the same for RT signals.  Here the instruction
 167    sequence is
 168        mov    $0xad, %eax
 169        int    $0x80
 170    or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80.
 171
 172    The effect is to call the system call rt_sigreturn.  */
 173
 174 #define LINUX_RT_SIGTRAMP_INSN0         0xb8 /* mov $NNNN, %eax */
 175 #define LINUX_RT_SIGTRAMP_OFFSET0       0
 176 #define LINUX_RT_SIGTRAMP_INSN1         0xcd /* int */
 177 #define LINUX_RT_SIGTRAMP_OFFSET1       5
 178
 179 static const gdb_byte linux_rt_sigtramp_code[] =
 180 {
 181   LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00,      /* mov $0xad, %eax */
 182   LINUX_RT_SIGTRAMP_INSN1, 0x80                         /* int $0x80 */
 183 };
 184
 185 #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code)
 186
 187 /* If NEXT_FRAME unwinds into an RT sigtramp routine, return the
 188    address of the start of the routine.  Otherwise, return 0.  */
 189
 190 static CORE_ADDR
 191 i386_linux_rt_sigtramp_start (struct frame_info *next_frame)
 192 {
 193   CORE_ADDR pc = frame_pc_unwind (next_frame);
 194   gdb_byte buf[LINUX_RT_SIGTRAMP_LEN];
 195
 196   /* We only recognize a signal trampoline if PC is at the start of
 197      one of the two instructions.  We optimize for finding the PC at
 198      the start, as will be the case when the trampoline is not the
 199      first frame on the stack.  We assume that in the case where the
 200      PC is not at the start of the instruction sequence, there will be
 201      a few trailing readable bytes on the stack.  */
 202
 203   if (!safe_frame_unwind_memory (next_frame, pc, buf, LINUX_RT_SIGTRAMP_LEN))
 204     return 0;
 205
 206   if (buf[0] != LINUX_RT_SIGTRAMP_INSN0)
 207     {
 208       if (buf[0] != LINUX_RT_SIGTRAMP_INSN1)
 209         return 0;
 210
 211       pc -= LINUX_RT_SIGTRAMP_OFFSET1;
 212
 213       if (!safe_frame_unwind_memory (next_frame, pc, buf,
 214                                      LINUX_RT_SIGTRAMP_LEN))
 215         return 0;
 216     }
 217
 218   if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0)
 219     return 0;
 220
 221   return pc;
 222 }
 223
 224 /* Return whether the frame preceding NEXT_FRAME corresponds to a
 225    GNU/Linux sigtramp routine.  */
 226
 227 static int
 228 i386_linux_sigtramp_p (struct frame_info *next_frame)
 229 {
 230   CORE_ADDR pc = frame_pc_unwind (next_frame);
 231   char *name;
 232
 233   find_pc_partial_function (pc, &name, NULL, NULL);
 234
 235   /* If we have NAME, we can optimize the search.  The trampolines are
 236      named __restore and __restore_rt.  However, they aren't dynamically
 237      exported from the shared C library, so the trampoline may appear to
 238      be part of the preceding function.  This should always be sigaction,
 239      __sigaction, or __libc_sigaction (all aliases to the same function).  */
 240   if (name == NULL || strstr (name, "sigaction") != NULL)
 241     return (i386_linux_sigtramp_start (next_frame) != 0
 242             || i386_linux_rt_sigtramp_start (next_frame) != 0);
 243
 244   return (strcmp ("__restore", name) == 0
 245           || strcmp ("__restore_rt", name) == 0);
 246 }
 247
 248 /* Return one if the unwound PC from NEXT_FRAME is in a signal trampoline
 249    which may have DWARF-2 CFI.  */
 250
 251 static int
 252 i386_linux_dwarf_signal_frame_p (struct gdbarch *gdbarch,
 253                                  struct frame_info *next_frame)
 254 {
 255   CORE_ADDR pc = frame_pc_unwind (next_frame);
 256   char *name;
 257
 258   find_pc_partial_function (pc, &name, NULL, NULL);
 259
 260   /* If a vsyscall DSO is in use, the signal trampolines may have these
 261      names.  */
 262   if (name && (strcmp (name, "__kernel_sigreturn") == 0
 263                || strcmp (name, "__kernel_rt_sigreturn") == 0))
 264     return 1;
 265
 266   return 0;
 267 }
 268
 269 /* Offset to struct sigcontext in ucontext, from <asm/ucontext.h>.  */
 270 #define I386_LINUX_UCONTEXT_SIGCONTEXT_OFFSET 20
 271
 272 /* Assuming NEXT_FRAME is a frame following a GNU/Linux sigtramp
 273    routine, return the address of the associated sigcontext structure.  */
 274
 275 static CORE_ADDR
 276 i386_linux_sigcontext_addr (struct frame_info *next_frame)
 277 {
 278   CORE_ADDR pc;
 279   CORE_ADDR sp;
 280   gdb_byte buf[4];
 281
 282   frame_unwind_register (next_frame, I386_ESP_REGNUM, buf);
 283   sp = extract_unsigned_integer (buf, 4);
 284
 285   pc = i386_linux_sigtramp_start (next_frame);
 286   if (pc)
 287     {
 288       /* The sigcontext structure lives on the stack, right after
 289          the signum argument.  We determine the address of the
 290          sigcontext structure by looking at the frame's stack
 291          pointer.  Keep in mind that the first instruction of the
 292          sigtramp code is "pop %eax".  If the PC is after this
 293          instruction, adjust the returned value accordingly.  */
 294       if (pc == frame_pc_unwind (next_frame))
 295         return sp + 4;
 296       return sp;
 297     }
 298
 299   pc = i386_linux_rt_sigtramp_start (next_frame);
 300   if (pc)
 301     {
 302       CORE_ADDR ucontext_addr;
 303
 304       /* The sigcontext structure is part of the user context.  A
 305          pointer to the user context is passed as the third argument
 306          to the signal handler.  */
 307       read_memory (sp + 8, buf, 4);
 308       ucontext_addr = extract_unsigned_integer (buf, 4);
 309       return ucontext_addr + I386_LINUX_UCONTEXT_SIGCONTEXT_OFFSET;
 310     }
 311
 312   error (_("Couldn't recognize signal trampoline."));
 313   return 0;
 314 }
 315
 316 /* Set the program counter for process PTID to PC.  */
 317
 318 static void
 319 i386_linux_write_pc (CORE_ADDR pc, ptid_t ptid)
 320 {
 321   write_register_pid (I386_EIP_REGNUM, pc, ptid);
 322
 323   /* We must be careful with modifying the program counter.  If we
 324      just interrupted a system call, the kernel might try to restart
 325      it when we resume the inferior.  On restarting the system call,
 326      the kernel will try backing up the program counter even though it
 327      no longer points at the system call.  This typically results in a
 328      SIGSEGV or SIGILL.  We can prevent this by writing `-1' in the
 329      "orig_eax" pseudo-register.
 330
 331      Note that "orig_eax" is saved when setting up a dummy call frame.
 332      This means that it is properly restored when that frame is
 333      popped, and that the interrupted system call will be restarted
 334      when we resume the inferior on return from a function call from
 335      within GDB.  In all other cases the system call will not be
 336      restarted.  */
 337   write_register_pid (I386_LINUX_ORIG_EAX_REGNUM, -1, ptid);
 338 }
 339 \f
 340
 341 /* The register sets used in GNU/Linux ELF core-dumps are identical to
 342    the register sets in `struct user' that are used for a.out
 343    core-dumps.  These are also used by ptrace(2).  The corresponding
 344    types are `elf_gregset_t' for the general-purpose registers (with
 345    `elf_greg_t' the type of a single GP register) and `elf_fpregset_t'
 346    for the floating-point registers.
 347
 348    Those types used to be available under the names `gregset_t' and
 349    `fpregset_t' too, and GDB used those names in the past.  But those
 350    names are now used for the register sets used in the `mcontext_t'
 351    type, which have a different size and layout.  */
 352
 353 /* Mapping between the general-purpose registers in `struct user'
 354    format and GDB's register cache layout.  */
 355
 356 /* From <sys/reg.h>.  */
 357 static int i386_linux_gregset_reg_offset[] =
 358 {
 359   6 * 4,                        /* %eax */
 360   1 * 4,                        /* %ecx */
 361   2 * 4,                        /* %edx */
 362   0 * 4,                        /* %ebx */
 363   15 * 4,                       /* %esp */
 364   5 * 4,                        /* %ebp */
 365   3 * 4,                        /* %esi */
 366   4 * 4,                        /* %edi */
 367   12 * 4,                       /* %eip */
 368   14 * 4,                       /* %eflags */
 369   13 * 4,                       /* %cs */
 370   16 * 4,                       /* %ss */
 371   7 * 4,                        /* %ds */
 372   8 * 4,                        /* %es */
 373   9 * 4,                        /* %fs */
 374   10 * 4,                       /* %gs */
 375   -1, -1, -1, -1, -1, -1, -1, -1,
 376   -1, -1, -1, -1, -1, -1, -1, -1,
 377   -1, -1, -1, -1, -1, -1, -1, -1,
 378   -1,
 379   11 * 4                        /* "orig_eax" */
 380 };
 381
 382 /* Mapping between the general-purpose registers in `struct
 383    sigcontext' format and GDB's register cache layout.  */
 384
 385 /* From <asm/sigcontext.h>.  */
 386 static int i386_linux_sc_reg_offset[] =
 387 {
 388   11 * 4,                       /* %eax */
 389   10 * 4,                       /* %ecx */
 390   9 * 4,                        /* %edx */
 391   8 * 4,                        /* %ebx */
 392   7 * 4,                        /* %esp */
 393   6 * 4,                        /* %ebp */
 394   5 * 4,                        /* %esi */
 395   4 * 4,                        /* %edi */
 396   14 * 4,                       /* %eip */
 397   16 * 4,                       /* %eflags */
 398   15 * 4,                       /* %cs */
 399   18 * 4,                       /* %ss */
 400   3 * 4,                        /* %ds */
 401   2 * 4,                        /* %es */
 402   1 * 4,                        /* %fs */
 403   0 * 4                         /* %gs */
 404 };
 405
 406 static void
 407 i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 408 {
 409   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
 410
 411   /* GNU/Linux uses ELF.  */
 412   i386_elf_init_abi (info, gdbarch);
 413
 414   /* Since we have the extra "orig_eax" register on GNU/Linux, we have
 415      to adjust a few things.  */
 416
 417   set_gdbarch_write_pc (gdbarch, i386_linux_write_pc);
 418   set_gdbarch_num_regs (gdbarch, I386_LINUX_NUM_REGS);
 419   set_gdbarch_register_name (gdbarch, i386_linux_register_name);
 420   set_gdbarch_register_reggroup_p (gdbarch, i386_linux_register_reggroup_p);
 421
 422   tdep->gregset_reg_offset = i386_linux_gregset_reg_offset;
 423   tdep->gregset_num_regs = ARRAY_SIZE (i386_linux_gregset_reg_offset);
 424   tdep->sizeof_gregset = 17 * 4;
 425
 426   tdep->jb_pc_offset = 20;      /* From <bits/setjmp.h>.  */
 427
 428   tdep->sigtramp_p = i386_linux_sigtramp_p;
 429   tdep->sigcontext_addr = i386_linux_sigcontext_addr;
 430   tdep->sc_reg_offset = i386_linux_sc_reg_offset;
 431   tdep->sc_num_regs = ARRAY_SIZE (i386_linux_sc_reg_offset);
 432
 433   /* GNU/Linux uses SVR4-style shared libraries.  */
 434   set_solib_svr4_fetch_link_map_offsets
 435     (gdbarch, svr4_ilp32_fetch_link_map_offsets);
 436
 437   /* GNU/Linux uses the dynamic linker included in the GNU C Library.  */
 438   set_gdbarch_skip_solib_resolver (gdbarch, glibc_skip_solib_resolver);
 439
 440   dwarf2_frame_set_signal_frame_p (gdbarch, i386_linux_dwarf_signal_frame_p);
 441
 442   /* Enable TLS support.  */
 443   set_gdbarch_fetch_tls_load_module_address (gdbarch,
 444                                              svr4_fetch_objfile_link_map);
 445 }
 446
 447 /* Provide a prototype to silence -Wmissing-prototypes.  */
 448 extern void _initialize_i386_linux_tdep (void);
 449
 450 void
 451 _initialize_i386_linux_tdep (void)
 452 {
 453   gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_LINUX,
 454                           i386_linux_init_abi);
 455 }