glibc/sysdeps/i386/dl-machine.h

/* Machine-dependent ELF dynamic relocation inline functions.  i386 version.
   Copyright (C) 1995, 1996, 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#ifndef dl_machine_h
#define dl_machine_h

#define ELF_MACHINE_NAME "i386"

#include <sys/param.h>

#include <assert.h>

/* Return nonzero iff E_MACHINE is compatible with the running host.  */
static inline int __attribute__ ((unused))
elf_machine_matches_host (Elf32_Half e_machine)
{
  switch (e_machine)
    {
    case EM_386:
    case EM_486:
      return 1;
    default:
      return 0;
    }
}


/* Return the link-time address of _DYNAMIC.  Conveniently, this is the
   first element of the GOT.  This must be inlined in a function which
   uses global data.  */
static inline Elf32_Addr
elf_machine_dynamic (void)
{
  register Elf32_Addr *got asm ("%ebx");
  return *got;
}


/* Return the run-time load address of the shared object.  */
static inline Elf32_Addr __attribute__ ((unused))
elf_machine_load_address (void)
{
  Elf32_Addr addr;
  asm ("	call .Lhere\n"
       ".Lhere:	popl %0\n"
       "	subl $.Lhere, %0"
       : "=r" (addr));
  return addr;
}
/* The `subl' insn above will contain an R_386_32 relocation entry
   intended to insert the run-time address of the label `.Lhere'.
   This will be the first relocation in the text of the dynamic linker;
   we skip it to avoid trying to modify read-only text in this early stage.  */
#define ELF_MACHINE_BEFORE_RTLD_RELOC(dynamic_info) \
  ++(const Elf32_Rel *) (dynamic_info)[DT_REL]->d_un.d_ptr; \
  (dynamic_info)[DT_RELSZ]->d_un.d_val -= sizeof (Elf32_Rel);


#ifndef PROF
/* We add a declaration of this function here so that in dl-runtime.c
   the ELF_MACHINE_RUNTIME_TRAMPOLINE macro really can pass the parameters
   in registers.

   We cannot use this scheme for profiling because the _mcount call
   destroys the passed register information.  */
static ElfW(Addr) fixup (struct link_map *l, ElfW(Word) reloc_offset)
     __attribute__ ((regparm (2), unused));
#endif

/* Set up the loaded object described by L so its unrelocated PLT
   entries will jump to the on-demand fixup code in dl-runtime.c.  */

static inline int
elf_machine_runtime_setup (struct link_map *l, int lazy)
{
  Elf32_Addr *got;
  extern void _dl_runtime_resolve (Elf32_Word);

  if (l->l_info[DT_JMPREL] && lazy)
    {
      /* The GOT entries for functions in the PLT have not yet been filled
	 in.  Their initial contents will arrange when called to push an
	 offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
	 and then jump to _GLOBAL_OFFSET_TABLE[2].  */
      got = (Elf32_Addr *) (l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr);
      got[1] = (Elf32_Addr) l;	/* Identify this shared object.  */
      /* This function will get called to fix up the GOT entry indicated by
	 the offset on the stack, and then jump to the resolved address.  */
      got[2] = (Elf32_Addr) &_dl_runtime_resolve;
    }

  return lazy;
}

/* This code is used in dl-runtime.c to call the `fixup' function
   and then redirect to the address it returns.  */
#ifndef PROF
# define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
	.globl _dl_runtime_resolve
	.type _dl_runtime_resolve, @function
_dl_runtime_resolve:
	pushl %eax		# Preserve registers otherwise clobbered.
	pushl %ecx
	pushl %edx
	movl 16(%esp), %edx	# Copy args pushed by PLT in register.  Note
	movl 12(%esp), %eax	# that `fixup' takes its parameters in regs.
	call fixup		# Call resolver.
	popl %edx		# Get register content back.
	popl %ecx
	xchgl %eax, (%esp)	# Get %eax contents end store function address.
	ret $8			# Jump to function address.
	.size _dl_runtime_resolve, .-_dl_runtime_resolve
");
#else
# define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
	.globl _dl_runtime_resolve
	.type _dl_runtime_resolve, @function
_dl_runtime_resolve:
	pushl %eax		# Preserve registers otherwise clobbered.
	pushl %ecx
	pushl %edx
	movl 16(%esp), %edx	# Push the arguments for `fixup'
	movl 12(%esp), %eax
	pushl %edx
	pushl %eax
	call fixup		# Call resolver.
	popl %edx		# Pop the parameters
	popl %ecx
	popl %edx		# Get register content back.
	popl %ecx
	xchgl %eax, (%esp)	# Get %eax contents end store function address.
	ret $8			# Jump to function address.
	.size _dl_runtime_resolve, .-_dl_runtime_resolve
");
#endif
/* The PLT uses Elf32_Rel relocs.  */
#define elf_machine_relplt elf_machine_rel

/* Mask identifying addresses reserved for the user program,
   where the dynamic linker should not map anything.  */
#define ELF_MACHINE_USER_ADDRESS_MASK	0xf8000000UL



/* Initial entry point code for the dynamic linker.
   The C function `_dl_start' is the real entry point;
   its return value is the user program's entry point.  */

#define RTLD_START asm ("\
.text\n\
.globl _start\n\
.globl _dl_start_user\n\
_start:\n\
	pushl %esp\n\
	call _dl_start\n\
	popl %ebx\n\
_dl_start_user:\n\
	# Save the user entry point address in %edi.\n\
	movl %eax, %edi\n\
	# Point %ebx at the GOT.
	call 0f\n\
0:	popl %ebx\n\
	addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ebx\n\
	# See if we were run as a command with the executable file\n\
	# name as an extra leading argument.\n\
	movl _dl_skip_args@GOT(%ebx), %eax\n\
	movl (%eax), %eax\n\
	# Pop the original argument count.\n\
	popl %ecx\n\
	# Subtract _dl_skip_args from it.\n\
	subl %eax, %ecx\n\
	# Adjust the stack pointer to skip _dl_skip_args words.\n\
	leal (%esp,%eax,4), %esp\n\
	# Push back the modified argument count.\n\
	pushl %ecx\n\
	# Push _dl_default_scope[2] as argument in _dl_init_next call below.\n\
	movl _dl_default_scope@GOT(%ebx), %eax\n\
	movl 8(%eax), %esi\n\
0:	pushl %esi\n\
	# Call _dl_init_next to return the address of an initializer\n\
	# function to run.\n\
	call _dl_init_next@PLT\n\
	addl $4, %esp # Pop argument.\n\
	# Check for zero return, when out of initializers.\n\
	testl %eax, %eax\n\
	jz 1f\n\
	# Call the shared object initializer function.\n\
	# NOTE: We depend only on the registers (%ebx, %esi and %edi)\n\
	# and the return address pushed by this call;\n\
	# the initializer is called with the stack just\n\
	# as it appears on entry, and it is free to move\n\
	# the stack around, as long as it winds up jumping to\n\
	# the return address on the top of the stack.\n\
	call *%eax\n\
	# Loop to call _dl_init_next for the next initializer.\n\
	jmp 0b\n\
1:	# Clear the startup flag.\n\
	movl _dl_starting_up@GOT(%ebx), %eax\n\
	movl $0, (%eax)\n\
	# Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
	movl _dl_fini@GOT(%ebx), %edx\n\
	# Jump to the user's entry point.\n\
	jmp *%edi\n\
");

/* Nonzero iff TYPE should not be allowed to resolve to one of
   the main executable's symbols, as for a COPY reloc.  */
#define elf_machine_lookup_noexec_p(type) ((type) == R_386_COPY)

/* Nonzero iff TYPE describes relocation of a PLT entry, so
   PLT entries should not be allowed to define the value.  */
#define elf_machine_lookup_noplt_p(type) ((type) == R_386_JMP_SLOT)

/* A reloc type used for ld.so cmdline arg lookups to reject PLT entries.  */
#define ELF_MACHINE_RELOC_NOPLT	R_386_JMP_SLOT

/* The i386 never uses Elf32_Rela relocations.  */
#define ELF_MACHINE_NO_RELA 1

#endif /* !dl_machine_h */

#ifdef RESOLVE

extern char **_dl_argv;

/* Perform the relocation specified by RELOC and SYM (which is fully resolved).
   MAP is the object containing the reloc.  */

static inline void
elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
		 const Elf32_Sym *sym, const struct r_found_version *version)
{
  Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);

  if (ELF32_R_TYPE (reloc->r_info) == R_386_RELATIVE)
    {
#ifndef RTLD_BOOTSTRAP
      if (map != &_dl_rtld_map) /* Already done in rtld itself.  */
#endif
	*reloc_addr += map->l_addr;
    }
  else if (ELF32_R_TYPE (reloc->r_info) != R_386_NONE)
    {
      const Elf32_Sym *const refsym = sym;
      Elf32_Addr value = RESOLVE (&sym, version, ELF32_R_TYPE (reloc->r_info));
      if (sym)
	value += sym->st_value;

      switch (ELF32_R_TYPE (reloc->r_info))
	{
	case R_386_COPY:
	  if (sym == NULL)
	    /* This can happen in trace mode if an object could not be
	       found.  */
	    break;
	  if (sym->st_size > refsym->st_size
	      || (_dl_verbose && sym->st_size < refsym->st_size))
	    {
	      const char *strtab;

	      strtab = ((void *) map->l_addr
			+ map->l_info[DT_STRTAB]->d_un.d_ptr);
	      _dl_sysdep_error ("Symbol `", strtab + refsym->st_name,
				"' in `",
				_dl_argv[0] ?: "<program name unknown>",
				"' has different size in shared object, "
				"consider re-linking\n", NULL);
	    }
	  memcpy (reloc_addr, (void *) value, MIN (sym->st_size,
						   refsym->st_size));
	  break;
	case R_386_GLOB_DAT:
	case R_386_JMP_SLOT:
	  *reloc_addr = value;
	  break;
	case R_386_32:
	  {
#ifndef RTLD_BOOTSTRAP
	   /* This is defined in rtld.c, but nowhere in the static
	      libc.a; make the reference weak so static programs can
	      still link.  This declaration cannot be done when
	      compiling rtld.c (i.e.  #ifdef RTLD_BOOTSTRAP) because
	      rtld.c contains the common defn for _dl_rtld_map, which
	      is incompatible with a weak decl in the same file.  */
	    weak_extern (_dl_rtld_map);
	    if (map == &_dl_rtld_map)
	      /* Undo the relocation done here during bootstrapping.
		 Now we will relocate it anew, possibly using a
		 binding found in the user program or a loaded library
		 rather than the dynamic linker's built-in definitions
		 used while loading those libraries.  */
	      value -= map->l_addr + refsym->st_value;
#endif
	    *reloc_addr += value;
	    break;
	  }
	case R_386_PC32:
	  *reloc_addr += (value - (Elf32_Addr) reloc_addr);
	  break;
	default:
	  assert (! "unexpected dynamic reloc type");
	  break;
	}
    }
}

static inline void
elf_machine_lazy_rel (struct link_map *map, const Elf32_Rel *reloc)
{
  Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
  switch (ELF32_R_TYPE (reloc->r_info))
    {
    case R_386_JMP_SLOT:
      *reloc_addr += map->l_addr;
      break;
    default:
      assert (! "unexpected PLT reloc type");
      break;
    }
}

#endif /* RESOLVE */