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/* Target-dependent code for GNU/Linux i386.

   Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2008

   Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"

#include "gdbcore.h"

#include "frame.h"

#include "value.h"

#include "regcache.h"

#include "inferior.h"

#include "osabi.h"

#include "reggroups.h"

#include "dwarf2-frame.h"

#include "gdb_string.h"

#include "i386-tdep.h"

#include "i386-linux-tdep.h"

#include "glibc-tdep.h"

#include "solib-svr4.h"

#include "symtab.h"

/* Return the name of register REG.  */

static const char *

i386_linux_register_name (struct gdbarch *gdbarch, int reg)

{

  /* Deal with the extra "orig_eax" pseudo register.  */

  if (reg == I386_LINUX_ORIG_EAX_REGNUM)

    return "orig_eax";

  return i386_register_name (gdbarch, reg);

}

/* Return non-zero, when the register is in the corresponding register

   group.  Put the LINUX_ORIG_EAX register in the system group.  */

static int

i386_linux_register_reggroup_p (struct gdbarch *gdbarch, int regnum,

                                struct reggroup *group)

{

  if (regnum == I386_LINUX_ORIG_EAX_REGNUM)

    return (group == system_reggroup

            || group == save_reggroup

            || group == restore_reggroup);

  return i386_register_reggroup_p (gdbarch, regnum, group);

}

/* Recognizing signal handler frames.  */

/* GNU/Linux has two flavors of signals.  Normal signal handlers, and

   "realtime" (RT) signals.  The RT signals can provide additional

   information to the signal handler if the SA_SIGINFO flag is set

   when establishing a signal handler using `sigaction'.  It is not

   unlikely that future versions of GNU/Linux will support SA_SIGINFO

   for normal signals too.  */

/* When the i386 Linux kernel calls a signal handler and the

   SA_RESTORER flag isn't set, the return address points to a bit of

   code on the stack.  This function returns whether the PC appears to

   be within this bit of code.

   The instruction sequence for normal signals is

       pop    %eax

       mov    $0x77, %eax

       int    $0x80

   or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80.

   Checking for the code sequence should be somewhat reliable, because

   the effect is to call the system call sigreturn.  This is unlikely

   to occur anywhere other than in a signal trampoline.

   It kind of sucks that we have to read memory from the process in

   order to identify a signal trampoline, but there doesn't seem to be

   any other way.  Therefore we only do the memory reads if no

   function name could be identified, which should be the case since

   the code is on the stack.

   Detection of signal trampolines for handlers that set the

   SA_RESTORER flag is in general not possible.  Unfortunately this is

   what the GNU C Library has been doing for quite some time now.

   However, as of version 2.1.2, the GNU C Library uses signal

   trampolines (named __restore and __restore_rt) that are identical

   to the ones used by the kernel.  Therefore, these trampolines are

   supported too.  */

#define LINUX_SIGTRAMP_INSN0    0x58    /* pop %eax */

#define LINUX_SIGTRAMP_OFFSET0  0

#define LINUX_SIGTRAMP_INSN1    0xb8    /* mov $NNNN, %eax */

#define LINUX_SIGTRAMP_OFFSET1  1

#define LINUX_SIGTRAMP_INSN2    0xcd    /* int */

#define LINUX_SIGTRAMP_OFFSET2  6

static const gdb_byte linux_sigtramp_code[] =

{

  LINUX_SIGTRAMP_INSN0,                                 /* pop %eax */

  LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00,         /* mov $0x77, %eax */

  LINUX_SIGTRAMP_INSN2, 0x80                            /* int $0x80 */

};

#define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code)

/* If NEXT_FRAME unwinds into a sigtramp routine, return the address

   of the start of the routine.  Otherwise, return 0.  */

static CORE_ADDR

i386_linux_sigtramp_start (struct frame_info *next_frame)

{

  CORE_ADDR pc = frame_pc_unwind (next_frame);

  gdb_byte buf[LINUX_SIGTRAMP_LEN];

  /* We only recognize a signal trampoline if PC is at the start of

     one of the three instructions.  We optimize for finding the PC at

     the start, as will be the case when the trampoline is not the

     first frame on the stack.  We assume that in the case where the

     PC is not at the start of the instruction sequence, there will be

     a few trailing readable bytes on the stack.  */

  if (!safe_frame_unwind_memory (next_frame, pc, buf, LINUX_SIGTRAMP_LEN))

    return 0;

  if (buf[0] != LINUX_SIGTRAMP_INSN0)

    {

      int adjust;

      switch (buf[0])

        {

        case LINUX_SIGTRAMP_INSN1:

          adjust = LINUX_SIGTRAMP_OFFSET1;

          break;

        case LINUX_SIGTRAMP_INSN2:

          adjust = LINUX_SIGTRAMP_OFFSET2;

          break;

        default:

          return 0;

        }

      pc -= adjust;

      if (!safe_frame_unwind_memory (next_frame, pc, buf, LINUX_SIGTRAMP_LEN))

        return 0;

    }

  if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0)

    return 0;

  return pc;

}

/* This function does the same for RT signals.  Here the instruction

   sequence is

       mov    $0xad, %eax

       int    $0x80

   or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80.

   The effect is to call the system call rt_sigreturn.  */

#define LINUX_RT_SIGTRAMP_INSN0         0xb8 /* mov $NNNN, %eax */

#define LINUX_RT_SIGTRAMP_OFFSET0       0

#define LINUX_RT_SIGTRAMP_INSN1         0xcd /* int */

#define LINUX_RT_SIGTRAMP_OFFSET1       5

static const gdb_byte linux_rt_sigtramp_code[] =

{

  LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00,      /* mov $0xad, %eax */

  LINUX_RT_SIGTRAMP_INSN1, 0x80                         /* int $0x80 */

};

#define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code)

/* If NEXT_FRAME unwinds into an RT sigtramp routine, return the

   address of the start of the routine.  Otherwise, return 0.  */

static CORE_ADDR

i386_linux_rt_sigtramp_start (struct frame_info *next_frame)

{

  CORE_ADDR pc = frame_pc_unwind (next_frame);

  gdb_byte buf[LINUX_RT_SIGTRAMP_LEN];

  /* We only recognize a signal trampoline if PC is at the start of

     one of the two instructions.  We optimize for finding the PC at

     the start, as will be the case when the trampoline is not the

     first frame on the stack.  We assume that in the case where the

     PC is not at the start of the instruction sequence, there will be

     a few trailing readable bytes on the stack.  */

  if (!safe_frame_unwind_memory (next_frame, pc, buf, LINUX_RT_SIGTRAMP_LEN))

    return 0;

  if (buf[0] != LINUX_RT_SIGTRAMP_INSN0)

    {

      if (buf[0] != LINUX_RT_SIGTRAMP_INSN1)

        return 0;

      pc -= LINUX_RT_SIGTRAMP_OFFSET1;

      if (!safe_frame_unwind_memory (next_frame, pc, buf,

                                     LINUX_RT_SIGTRAMP_LEN))

        return 0;

    }

  if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0)

    return 0;

  return pc;

}

/* Return whether the frame preceding NEXT_FRAME corresponds to a

   GNU/Linux sigtramp routine.  */

static int

i386_linux_sigtramp_p (struct frame_info *next_frame)

{

  CORE_ADDR pc = frame_pc_unwind (next_frame);

  char *name;

  find_pc_partial_function (pc, &name, NULL, NULL);

  /* If we have NAME, we can optimize the search.  The trampolines are

     named __restore and __restore_rt.  However, they aren't dynamically

     exported from the shared C library, so the trampoline may appear to

     be part of the preceding function.  This should always be sigaction,

     __sigaction, or __libc_sigaction (all aliases to the same function).  */

  if (name == NULL || strstr (name, "sigaction") != NULL)

    return (i386_linux_sigtramp_start (next_frame) != 0

            || i386_linux_rt_sigtramp_start (next_frame) != 0);

  return (strcmp ("__restore", name) == 0

          || strcmp ("__restore_rt", name) == 0);

}

/* Return one if the unwound PC from NEXT_FRAME is in a signal trampoline

   which may have DWARF-2 CFI.  */

static int

i386_linux_dwarf_signal_frame_p (struct gdbarch *gdbarch,

                                 struct frame_info *next_frame)

{

  CORE_ADDR pc = frame_pc_unwind (next_frame);

  char *name;

  find_pc_partial_function (pc, &name, NULL, NULL);

  /* If a vsyscall DSO is in use, the signal trampolines may have these

     names.  */

  if (name && (strcmp (name, "__kernel_sigreturn") == 0

               || strcmp (name, "__kernel_rt_sigreturn") == 0))

    return 1;

  return 0;

}

/* Offset to struct sigcontext in ucontext, from <asm/ucontext.h>.  */

#define I386_LINUX_UCONTEXT_SIGCONTEXT_OFFSET 20

/* Assuming NEXT_FRAME is a frame following a GNU/Linux sigtramp

   routine, return the address of the associated sigcontext structure.  */

static CORE_ADDR

i386_linux_sigcontext_addr (struct frame_info *next_frame)

{

  CORE_ADDR pc;

  CORE_ADDR sp;

  gdb_byte buf[4];

  frame_unwind_register (next_frame, I386_ESP_REGNUM, buf);

  sp = extract_unsigned_integer (buf, 4);

  pc = i386_linux_sigtramp_start (next_frame);

  if (pc)

    {

      /* The sigcontext structure lives on the stack, right after

         the signum argument.  We determine the address of the

         sigcontext structure by looking at the frame's stack

         pointer.  Keep in mind that the first instruction of the

         sigtramp code is "pop %eax".  If the PC is after this

         instruction, adjust the returned value accordingly.  */

      if (pc == frame_pc_unwind (next_frame))

        return sp + 4;

      return sp;

    }

  pc = i386_linux_rt_sigtramp_start (next_frame);

  if (pc)

    {

      CORE_ADDR ucontext_addr;

      /* The sigcontext structure is part of the user context.  A

         pointer to the user context is passed as the third argument

         to the signal handler.  */

      read_memory (sp + 8, buf, 4);

      ucontext_addr = extract_unsigned_integer (buf, 4);

      return ucontext_addr + I386_LINUX_UCONTEXT_SIGCONTEXT_OFFSET;

    }

  error (_("Couldn't recognize signal trampoline."));

  return 0;

}

/* Set the program counter for process PTID to PC.  */

static void

i386_linux_write_pc (struct regcache *regcache, CORE_ADDR pc)

{

  regcache_cooked_write_unsigned (regcache, I386_EIP_REGNUM, pc);

  /* We must be careful with modifying the program counter.  If we

     just interrupted a system call, the kernel might try to restart

     it when we resume the inferior.  On restarting the system call,

     the kernel will try backing up the program counter even though it

     no longer points at the system call.  This typically results in a

     SIGSEGV or SIGILL.  We can prevent this by writing `-1' in the

     "orig_eax" pseudo-register.

     Note that "orig_eax" is saved when setting up a dummy call frame.

     This means that it is properly restored when that frame is

     popped, and that the interrupted system call will be restarted

     when we resume the inferior on return from a function call from

     within GDB.  In all other cases the system call will not be

     restarted.  */

  regcache_cooked_write_unsigned (regcache, I386_LINUX_ORIG_EAX_REGNUM, -1);

}

/* The register sets used in GNU/Linux ELF core-dumps are identical to

   the register sets in `struct user' that are used for a.out

   core-dumps.  These are also used by ptrace(2).  The corresponding

   types are `elf_gregset_t' for the general-purpose registers (with

   `elf_greg_t' the type of a single GP register) and `elf_fpregset_t'

   for the floating-point registers.

   Those types used to be available under the names `gregset_t' and

   `fpregset_t' too, and GDB used those names in the past.  But those

   names are now used for the register sets used in the `mcontext_t'

   type, which have a different size and layout.  */

/* Mapping between the general-purpose registers in `struct user'

   format and GDB's register cache layout.  */

/* From <sys/reg.h>.  */

static int i386_linux_gregset_reg_offset[] =

{

  6 * 4,                        /* %eax */

  1 * 4,                        /* %ecx */

  2 * 4,                        /* %edx */

  15 * 4,                       /* %esp */

  5 * 4,                        /* %ebp */

  3 * 4,                        /* %esi */

  4 * 4,                        /* %edi */

  12 * 4,                       /* %eip */

  14 * 4,                       /* %eflags */

  13 * 4,                       /* %cs */

  16 * 4,                       /* %ss */

  7 * 4,                        /* %ds */

  8 * 4,                        /* %es */

  9 * 4,                        /* %fs */

  10 * 4,                       /* %gs */

  -1, -1, -1, -1, -1, -1, -1, -1,

  -1, -1, -1, -1, -1, -1, -1, -1,

  -1, -1, -1, -1, -1, -1, -1, -1,

  -1,

  11 * 4                        /* "orig_eax" */

};

/* Mapping between the general-purpose registers in `struct

   sigcontext' format and GDB's register cache layout.  */

/* From <asm/sigcontext.h>.  */

static int i386_linux_sc_reg_offset[] =

{

  11 * 4,                       /* %eax */

  10 * 4,                       /* %ecx */

  9 * 4,                        /* %edx */

  8 * 4,                        /* %ebx */

  7 * 4,                        /* %esp */

  6 * 4,                        /* %ebp */

  5 * 4,                        /* %esi */

  4 * 4,                        /* %edi */

  14 * 4,                       /* %eip */

  16 * 4,                       /* %eflags */

  15 * 4,                       /* %cs */

  18 * 4,                       /* %ss */

  3 * 4,                        /* %ds */

  2 * 4,                        /* %es */

  1 * 4,                        /* %fs */

};

static void

i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)

{

  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

  /* GNU/Linux uses ELF.  */

  i386_elf_init_abi (info, gdbarch);

  /* Since we have the extra "orig_eax" register on GNU/Linux, we have

     to adjust a few things.  */

  set_gdbarch_write_pc (gdbarch, i386_linux_write_pc);

  set_gdbarch_num_regs (gdbarch, I386_LINUX_NUM_REGS);

  set_gdbarch_register_name (gdbarch, i386_linux_register_name);

  set_gdbarch_register_reggroup_p (gdbarch, i386_linux_register_reggroup_p);

  tdep->gregset_reg_offset = i386_linux_gregset_reg_offset;

  tdep->gregset_num_regs = ARRAY_SIZE (i386_linux_gregset_reg_offset);

  tdep->sizeof_gregset = 17 * 4;

  tdep->jb_pc_offset = 20;      /* From <bits/setjmp.h>.  */

  tdep->sigtramp_p = i386_linux_sigtramp_p;

  tdep->sigcontext_addr = i386_linux_sigcontext_addr;

  tdep->sc_reg_offset = i386_linux_sc_reg_offset;

  tdep->sc_num_regs = ARRAY_SIZE (i386_linux_sc_reg_offset);

  /* N_FUN symbols in shared libaries have 0 for their values and need

     to be relocated. */

  set_gdbarch_sofun_address_maybe_missing (gdbarch, 1);

  /* GNU/Linux uses SVR4-style shared libraries.  */

  set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target);

  set_solib_svr4_fetch_link_map_offsets

    (gdbarch, svr4_ilp32_fetch_link_map_offsets);

  /* GNU/Linux uses the dynamic linker included in the GNU C Library.  */

  set_gdbarch_skip_solib_resolver (gdbarch, glibc_skip_solib_resolver);

  dwarf2_frame_set_signal_frame_p (gdbarch, i386_linux_dwarf_signal_frame_p);

  /* Enable TLS support.  */

  set_gdbarch_fetch_tls_load_module_address (gdbarch,

                                             svr4_fetch_objfile_link_map);

}

/* Provide a prototype to silence -Wmissing-prototypes.  */

extern void _initialize_i386_linux_tdep (void);

void

_initialize_i386_linux_tdep (void)

{

  gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_LINUX,

                          i386_linux_init_abi);

}