glibc/sysdeps/i386/dl-machine.h

/* Machine-dependent ELF dynamic relocation inline functions.  i386 version.
Copyright (C) 1995, 1996 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., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#define ELF_MACHINE_NAME "i386"

#include <assert.h>
#include <string.h>
#include <link.h>


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


/* Return the run-time address of the _GLOBAL_OFFSET_TABLE_.
   Must be inlined in a function which uses global data.  */
static inline Elf32_Addr *
elf_machine_got (void)
{
  register Elf32_Addr *got asm ("%ebx");
  return got;
}


/* Return the run-time load address of the shared object.  */
static inline Elf32_Addr
elf_machine_load_address (void)
{
  Elf32_Addr addr;
  asm ("	call here\n"
       "here:	popl %0\n"
       "	subl $here, %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 `here'.
   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);

/* 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,
		 Elf32_Addr (*resolve) (const Elf32_Sym **ref,
					Elf32_Addr reloc_addr,
					int noplt))
{
  Elf32_Addr *const reloc_addr = (void *) (map->l_addr + reloc->r_offset);
  Elf32_Addr loadbase;

#ifdef RTLD_BOOTSTRAP
#define RESOLVE(noplt) map->l_addr
#else
#define RESOLVE(noplt) (*resolve) (&sym, (Elf32_Addr) reloc_addr, noplt)
#endif

  switch (ELF32_R_TYPE (reloc->r_info))
    {
    case R_386_COPY:
      loadbase = RESOLVE (0);
      memcpy (reloc_addr, (void *) (loadbase + sym->st_value), sym->st_size);
      break;
    case R_386_GLOB_DAT:
      loadbase = RESOLVE (0);
      *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
      break;
    case R_386_JMP_SLOT:
      loadbase = RESOLVE (1);
      *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
      break;
    case R_386_32:
      {
	Elf32_Addr undo = 0;
#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.  */
	  undo = map->l_addr + sym->st_value;
#endif
	loadbase = RESOLVE (0);
	*reloc_addr += (sym ? (loadbase + sym->st_value) : 0) - undo;
	break;
      }
    case R_386_RELATIVE:
      if (!resolve || map != &_dl_rtld_map) /* Already done in rtld itself.  */
	*reloc_addr += map->l_addr;
      break;
    case R_386_PC32:
      loadbase = RESOLVE (0);
      *reloc_addr += ((sym ? (loadbase + sym->st_value) : 0) -
		      (Elf32_Addr) reloc_addr);
      break;
    case R_386_NONE:		/* Alright, Wilbur.  */
      break;
    default:
      assert (! "unexpected dynamic reloc type");
      break;
    }

#undef RESOLVE
}

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;
    }
}

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

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


/* 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 void
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;
    }

  /* This code is used in dl-runtime.c to call the `fixup' function
     and then redirect to the address it returns.  */
#define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
	.globl _dl_runtime_resolve
	.type _dl_runtime_resolve, @function
_dl_runtime_resolve:
	call fixup	# Args pushed by PLT.
	addl $8, %esp	# Pop args.
	jmp *%eax	# Jump to function address.
");
/* 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:	# 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\
");