i386obsd-tdep.c   [plain text]

/* Target-dependent code for OpenBSD/i386.

   Copyright 1988, 1989, 1991, 1992, 1994, 1996, 2000, 2001, 2002,
   2003, 2004, 2005
   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 2 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, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include "defs.h"
#include "arch-utils.h"
#include "frame.h"
#include "gdbcore.h"
#include "regcache.h"
#include "regset.h"
#include "symtab.h"
#include "objfiles.h"
#include "osabi.h"
#include "target.h"

#include "gdb_assert.h"
#include "gdb_string.h"

#include "i386-tdep.h"
#include "i387-tdep.h"
#include "solib-svr4.h"
#include "bsd-uthread.h"

/* Support for signal handlers.  */

/* Since OpenBSD 3.2, the sigtramp routine is mapped at a random page
   in virtual memory.  The randomness makes it somewhat tricky to
   detect it, but fortunately we can rely on the fact that the start
   of the sigtramp routine is page-aligned.  We recognize the
   trampoline by looking for the code that invokes the sigreturn
   system call.  The offset where we can find that code varies from
   release to release.

   By the way, the mapping mentioned above is read-only, so you cannot
   place a breakpoint in the signal trampoline.  */

/* Default page size.  */
static const int i386obsd_page_size = 4096;

/* Offset for sigreturn(2).  */
static const int i386obsd_sigreturn_offset[] = {
  0x0a,				/* OpenBSD 3.2 */
  0x14,				/* OpenBSD 3.6 */
  0x3a,				/* OpenBSD 3.8 */
  -1
};

/* Return whether the frame preceding NEXT_FRAME corresponds to an
   OpenBSD sigtramp routine.  */

static int
i386obsd_sigtramp_p (struct frame_info *next_frame)
{
  CORE_ADDR pc = frame_pc_unwind (next_frame);
  CORE_ADDR start_pc = (pc & ~(i386obsd_page_size - 1));
  /* The call sequence invoking sigreturn(2).  */
  const gdb_byte sigreturn[] =
  {
    0xb8,
    0x67, 0x00, 0x00, 0x00,	/* movl $SYS_sigreturn, %eax */
    0xcd, 0x80			/* int $0x80 */
  };
  size_t buflen = sizeof sigreturn;
  const int *offset;
  gdb_byte *buf;
  char *name;

  /* If the function has a valid symbol name, it isn't a
     trampoline.  */
  find_pc_partial_function (pc, &name, NULL, NULL);
  if (name != NULL)
    return 0;

  /* If the function lives in a valid section (even without a starting
     point) it isn't a trampoline.  */
  if (find_pc_section (pc) != NULL)
    return 0;

  /* Allocate buffer.  */
  buf = alloca (buflen);

  /* Loop over all offsets.  */
  for (offset = i386obsd_sigreturn_offset; *offset != -1; offset++)
    {
      /* If we can't read the instructions, return zero.  */
      if (!safe_frame_unwind_memory (next_frame, start_pc + *offset,
				     buf, buflen))
	return 0;

      /* Check for sigreturn(2).  */
      if (memcmp (buf, sigreturn, buflen) == 0)
	return 1;
    }

  return 0;
}

/* Mapping between the general-purpose registers in `struct reg'
   format and GDB's register cache layout.  */

/* From <machine/reg.h>.  */
static int i386obsd_r_reg_offset[] =
{
  0 * 4,			/* %eax */
  1 * 4,			/* %ecx */
  2 * 4,			/* %edx */
  3 * 4,			/* %ebx */
  4 * 4,			/* %esp */
  5 * 4,			/* %ebp */
  6 * 4,			/* %esi */
  7 * 4,			/* %edi */
  8 * 4,			/* %eip */
  9 * 4,			/* %eflags */
  10 * 4,			/* %cs */
  11 * 4,			/* %ss */
  12 * 4,			/* %ds */
  13 * 4,			/* %es */
  14 * 4,			/* %fs */
  15 * 4			/* %gs */
};

static void
i386obsd_aout_supply_regset (const struct regset *regset,
			     struct regcache *regcache, int regnum,
			     const void *regs, size_t len)
{
  const struct gdbarch_tdep *tdep = gdbarch_tdep (regset->arch);
  const gdb_byte *gregs = regs;

  gdb_assert (len >= tdep->sizeof_gregset + I387_SIZEOF_FSAVE);

  i386_supply_gregset (regset, regcache, regnum, regs, tdep->sizeof_gregset);
  i387_supply_fsave (regcache, regnum, gregs + tdep->sizeof_gregset);
}

static const struct regset *
i386obsd_aout_regset_from_core_section (struct gdbarch *gdbarch,
					const char *sect_name,
					size_t sect_size)
{
  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

  /* OpenBSD a.out core dumps don't use seperate register sets for the
     general-purpose and floating-point registers.  */

  if (strcmp (sect_name, ".reg") == 0
      && sect_size >= tdep->sizeof_gregset + I387_SIZEOF_FSAVE)
    {
      if (tdep->gregset == NULL)
        tdep->gregset =
	  regset_alloc (gdbarch, i386obsd_aout_supply_regset, NULL);
      return tdep->gregset;
    }

  return NULL;
}


/* Sigtramp routine location for OpenBSD 3.1 and earlier releases.  */
CORE_ADDR i386obsd_sigtramp_start_addr = 0xbfbfdf20;
CORE_ADDR i386obsd_sigtramp_end_addr = 0xbfbfdff0;

/* From <machine/signal.h>.  */
int i386obsd_sc_reg_offset[I386_NUM_GREGS] =
{
  10 * 4,			/* %eax */
  9 * 4,			/* %ecx */
  8 * 4,			/* %edx */
  7 * 4,			/* %ebx */
  14 * 4,			/* %esp */
  6 * 4,			/* %ebp */
  5 * 4,			/* %esi */
  4 * 4,			/* %edi */
  11 * 4,			/* %eip */
  13 * 4,			/* %eflags */
  12 * 4,			/* %cs */
  15 * 4,			/* %ss */
  3 * 4,			/* %ds */
  2 * 4,			/* %es */
  1 * 4,			/* %fs */
  0 * 4				/* %gs */
};

/* From /usr/src/lib/libpthread/arch/i386/uthread_machdep.c.  */
static int i386obsd_uthread_reg_offset[] =
{
  11 * 4,			/* %eax */
  10 * 4,			/* %ecx */
  9 * 4,			/* %edx */
  8 * 4,			/* %ebx */
  -1,				/* %esp */
  6 * 4,			/* %ebp */
  5 * 4,			/* %esi */
  4 * 4,			/* %edi */
  12 * 4,			/* %eip */
  -1,				/* %eflags */
  13 * 4,			/* %cs */
  -1,				/* %ss */
  3 * 4,			/* %ds */
  2 * 4,			/* %es */
  1 * 4,			/* %fs */
  0 * 4				/* %gs */
};

/* Offset within the thread structure where we can find the saved
   stack pointer (%esp).  */
#define I386OBSD_UTHREAD_ESP_OFFSET	176

static void
i386obsd_supply_uthread (struct regcache *regcache,
			 int regnum, CORE_ADDR addr)
{
  CORE_ADDR sp_addr = addr + I386OBSD_UTHREAD_ESP_OFFSET;
  CORE_ADDR sp = 0;
  gdb_byte buf[4];
  int i;

  gdb_assert (regnum >= -1);

  if (regnum == -1 || regnum == I386_ESP_REGNUM)
    {
      int offset;

      /* Fetch stack pointer from thread structure.  */
      sp = read_memory_unsigned_integer (sp_addr, 4);

      /* Adjust the stack pointer such that it looks as if we just
         returned from _thread_machdep_switch.  */
      offset = i386obsd_uthread_reg_offset[I386_EIP_REGNUM] + 4;
      store_unsigned_integer (buf, 4, sp + offset);
      regcache_raw_supply (regcache, I386_ESP_REGNUM, buf);
    }

  for (i = 0; i < ARRAY_SIZE (i386obsd_uthread_reg_offset); i++)
    {
      if (i386obsd_uthread_reg_offset[i] != -1
	  && (regnum == -1 || regnum == i))
	{
	  /* Fetch stack pointer from thread structure (if we didn't
             do so already).  */
	  if (sp == 0)
	    sp = read_memory_unsigned_integer (sp_addr, 4);

	  /* Read the saved register from the stack frame.  */
	  read_memory (sp + i386obsd_uthread_reg_offset[i], buf, 4);
	  regcache_raw_supply (regcache, i, buf);
	}
    }

}

static void
i386obsd_collect_uthread (const struct regcache *regcache,
			  int regnum, CORE_ADDR addr)
{
  CORE_ADDR sp_addr = addr + I386OBSD_UTHREAD_ESP_OFFSET;
  CORE_ADDR sp = 0;
  gdb_byte buf[4];
  int i;

  gdb_assert (regnum >= -1);

  if (regnum == -1 || regnum == I386_ESP_REGNUM)
    {
      int offset;

      /* Calculate the stack pointer (frame pointer) that will be
         stored into the thread structure.  */
      offset = i386obsd_uthread_reg_offset[I386_EIP_REGNUM] + 4;
      regcache_raw_collect (regcache, I386_ESP_REGNUM, buf);
      sp = extract_unsigned_integer (buf, 4) - offset;

      /* Store the stack pointer.  */
      write_memory_unsigned_integer (sp_addr, 4, sp);

      /* The stack pointer was (potentially) modified.  Make sure we
         build a proper stack frame.  */
      regnum = -1;
    }

  for (i = 0; i < ARRAY_SIZE (i386obsd_uthread_reg_offset); i++)
    {
      if (i386obsd_uthread_reg_offset[i] != -1
	  && (regnum == -1 || regnum == i))
	{
	  /* Fetch stack pointer from thread structure (if we didn't
             calculate it already).  */
	  if (sp == 0)
	    sp = read_memory_unsigned_integer (sp_addr, 4);

	  /* Write the register into the stack frame.  */
	  regcache_raw_collect (regcache, i, buf);
	  write_memory (sp + i386obsd_uthread_reg_offset[i], buf, 4);
	}
    }
}

static void 
i386obsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

  /* Obviously OpenBSD is BSD-based.  */
  i386bsd_init_abi (info, gdbarch);

  /* OpenBSD has a different `struct reg'.  */
  tdep->gregset_reg_offset = i386obsd_r_reg_offset;
  tdep->gregset_num_regs = ARRAY_SIZE (i386obsd_r_reg_offset);
  tdep->sizeof_gregset = 16 * 4;

  /* OpenBSD uses -freg-struct-return by default.  */
  tdep->struct_return = reg_struct_return;

  /* OpenBSD uses a different memory layout.  */
  tdep->sigtramp_start = i386obsd_sigtramp_start_addr;
  tdep->sigtramp_end = i386obsd_sigtramp_end_addr;
  tdep->sigtramp_p = i386obsd_sigtramp_p;

  /* OpenBSD has a `struct sigcontext' that's different from the
     original 4.3 BSD.  */
  tdep->sc_reg_offset = i386obsd_sc_reg_offset;
  tdep->sc_num_regs = ARRAY_SIZE (i386obsd_sc_reg_offset);

  /* OpenBSD provides a user-level threads implementation.  */
  bsd_uthread_set_supply_uthread (gdbarch, i386obsd_supply_uthread);
  bsd_uthread_set_collect_uthread (gdbarch, i386obsd_collect_uthread);
}

/* OpenBSD a.out.  */

static void
i386obsd_aout_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
  i386obsd_init_abi (info, gdbarch);

  /* OpenBSD a.out has a single register set.  */
  set_gdbarch_regset_from_core_section
    (gdbarch, i386obsd_aout_regset_from_core_section);
}

/* OpenBSD ELF.  */

static void
i386obsd_elf_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

  /* It's still OpenBSD.  */
  i386obsd_init_abi (info, gdbarch);

  /* But ELF-based.  */
  i386_elf_init_abi (info, gdbarch);

  /* OpenBSD ELF uses SVR4-style shared libraries.  */
  set_solib_svr4_fetch_link_map_offsets
    (gdbarch, svr4_ilp32_fetch_link_map_offsets);
}


/* Provide a prototype to silence -Wmissing-prototypes.  */
void _initialize_i386obsd_tdep (void);

void
_initialize_i386obsd_tdep (void)
{
  /* FIXME: kettenis/20021020: Since OpenBSD/i386 binaries are
     indistingushable from NetBSD/i386 a.out binaries, building a GDB
     that should support both these targets will probably not work as
     expected.  */
#define GDB_OSABI_OPENBSD_AOUT GDB_OSABI_NETBSD_AOUT

  gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_OPENBSD_AOUT,
			  i386obsd_aout_init_abi);
  gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_OPENBSD_ELF,
			  i386obsd_elf_init_abi);
}