[glibc.git] / 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;

  switch (ELF32_R_TYPE (reloc->r_info))
    {
    case R_386_COPY:
      loadbase = (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0);
      memcpy (reloc_addr, (void *) (loadbase + sym->st_value), sym->st_size);
      break;
    case R_386_GLOB_DAT:
      loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0) :
		  /* RESOLVE is null during bootstrap relocation.  */
		  map->l_addr);
      *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
      break;
    case R_386_JMP_SLOT:
      loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 1) :
		  /* RESOLVE is null during bootstrap relocation.  */
		  map->l_addr);
      *reloc_addr = sym ? (loadbase + sym->st_value) : 0;
      break;
    case R_386_32:
      if (map->l_type == lt_interpreter)
	{
	  /* 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.  */
	  const Elf32_Sym *const dlsymtab
	    = (void *) (map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
	  *reloc_addr -= (map->l_addr +
			  dlsymtab[ELF32_R_SYM (reloc->r_info)].st_value);
	}
      loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0) :
		  /* RESOLVE is null during bootstrap relocation.  */
		  map->l_addr);
      *reloc_addr += sym ? (loadbase + sym->st_value) : 0;
      break;
    case R_386_RELATIVE:
      if (map->l_type != lt_interpreter) /* Already done in dynamic linker.  */
	*reloc_addr += map->l_addr;
      break;
    case R_386_PC32:
      loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0) :
		  /* RESOLVE is null during bootstrap relocation.  */
		  map->l_addr);
      *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;
    }
}

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\
	call _dl_start\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_loaded as argument in _dl_init_next call below.\n\
	movl _dl_loaded@GOT(%ebx), %eax\n\
	movl (%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\
");
Commit	Line	Data
d66e34cd	1	/* Machine-dependent ELF dynamic relocation inline functions. i386 version.
a2e1b046	2	Copyright (C) 1995, 1996 Free Software Foundation, Inc.
d66e34cd RM	3	This file is part of the GNU C Library.
	4
	5	The GNU C Library is free software; you can redistribute it and/or
	6	modify it under the terms of the GNU Library General Public License as
	7	published by the Free Software Foundation; either version 2 of the
	8	License, or (at your option) any later version.
	9
	10	The GNU C Library is distributed in the hope that it will be useful,
	11	but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	13	Library General Public License for more details.
	14
	15	You should have received a copy of the GNU Library General Public
	16	License along with the GNU C Library; see the file COPYING.LIB. If
	17	not, write to the Free Software Foundation, Inc., 675 Mass Ave,
	18	Cambridge, MA 02139, USA. */
	19
	20	#define ELF_MACHINE_NAME "i386"
	21
	22	#include <assert.h>
	23	#include <string.h>
	24	#include <link.h>
	25
	26
	27	/* Return nonzero iff E_MACHINE is compatible with the running host. */
	28	static inline int
	29	elf_machine_matches_host (Elf32_Half e_machine)
	30	{
	31	switch (e_machine)
	32	{
	33	case EM_386:
	34	case EM_486:
	35	return 1;
	36	default:
	37	return 0;
	38	}
	39	}
	40
	41
	42	/* Return the run-time address of the _GLOBAL_OFFSET_TABLE_.
	43	Must be inlined in a function which uses global data. */
	44	static inline Elf32_Addr *
	45	elf_machine_got (void)
	46	{
	47	register Elf32_Addr *got asm ("%ebx");
	48	return got;
	49	}
	50
	51
	52	/* Return the run-time load address of the shared object. */
	53	static inline Elf32_Addr
	54	elf_machine_load_address (void)
	55	{
	56	Elf32_Addr addr;
	57	asm (" call here\n"
	58	"here: popl %0\n"
	59	" subl $here, %0"
	60	: "=r" (addr));
	61	return addr;
	62	}
	63	/* The `subl' insn above will contain an R_386_32 relocation entry
	64	intended to insert the run-time address of the label `here'.
	65	This will be the first relocation in the text of the dynamic linker;
	66	we skip it to avoid trying to modify read-only text in this early stage. */
67	#define ELF_MACHINE_BEFORE_RTLD_RELOC(dynamic_info) \
44c8d1a2	68	++(const Elf32_Rel *) (dynamic_info)[DT_REL]->d_un.d_ptr; \
a993273c	69	(dynamic_info)[DT_RELSZ]->d_un.d_val -= sizeof (Elf32_Rel);
d66e34cd RM	70
d66e34cd RM	71	/* Perform the relocation specified by RELOC and SYM (which is fully resolved).
421f82e5	72	MAP is the object containing the reloc. */
d66e34cd RM	73
d66e34cd RM	74	static inline void
421f82e5	75	elf_machine_rel (struct link_map *map,
710f7bab RM	76	const Elf32_Rel reloc, const Elf32_Sym sym,
	77	Elf32_Addr (resolve) (const Elf32_Sym *ref,
	78	Elf32_Addr reloc_addr,
	79	int noplt))
d66e34cd	80	{
a1a9d215	81	Elf32_Addr const reloc_addr = (void ) (map->l_addr + reloc->r_offset);
710f7bab	82	Elf32_Addr loadbase;
d66e34cd RM	83
	84	switch (ELF32_R_TYPE (reloc->r_info))
	85	{
	86	case R_386_COPY:
710f7bab RM	87	loadbase = (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0);
710f7bab RM	88	memcpy (reloc_addr, (void *) (loadbase + sym->st_value), sym->st_size);
d66e34cd RM	89	break;
d66e34cd RM	90	case R_386_GLOB_DAT:
710f7bab RM	91	loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0) :
	92	/* RESOLVE is null during bootstrap relocation. */
	93	map->l_addr);
	94	*reloc_addr = sym ? (loadbase + sym->st_value) : 0;
	95	break;
d66e34cd	96	case R_386_JMP_SLOT:
710f7bab RM	97	loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 1) :
	98	/* RESOLVE is null during bootstrap relocation. */
	99	map->l_addr);
	100	*reloc_addr = sym ? (loadbase + sym->st_value) : 0;
d66e34cd RM	101	break;
d66e34cd RM	102	case R_386_32:
5bf62f2d RM	103	if (map->l_type == lt_interpreter)
	104	{
	105	/* Undo the relocation done here during bootstrapping. Now we will
	106	relocate it anew, possibly using a binding found in the user
	107	program or a loaded library rather than the dynamic linker's
	108	built-in definitions used while loading those libraries. */
	109	const Elf32_Sym *const dlsymtab
	110	= (void *) (map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
	111	*reloc_addr -= (map->l_addr +
	112	dlsymtab[ELF32_R_SYM (reloc->r_info)].st_value);
	113	}
aa592a63 RM	114	loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0) :
	115	/* RESOLVE is null during bootstrap relocation. */
	116	map->l_addr);
710f7bab	117	*reloc_addr += sym ? (loadbase + sym->st_value) : 0;
d66e34cd RM	118	break;
d66e34cd RM	119	case R_386_RELATIVE:
5bf62f2d RM	120	if (map->l_type != lt_interpreter) /* Already done in dynamic linker. */
5bf62f2d RM	121	*reloc_addr += map->l_addr;
d66e34cd RM	122	break;
d66e34cd RM	123	case R_386_PC32:
aa592a63 RM	124	loadbase = (resolve ? (*resolve) (&sym, (Elf32_Addr) reloc_addr, 0) :
	125	/* RESOLVE is null during bootstrap relocation. */
	126	map->l_addr);
710f7bab RM	127	*reloc_addr += ((sym ? (loadbase + sym->st_value) : 0) -
710f7bab RM	128	(Elf32_Addr) reloc_addr);
d66e34cd	129	break;
86fe2915 RM	130	case R_386_NONE: /* Alright, Wilbur. */
86fe2915 RM	131	break;
d66e34cd RM	132	default:
	133	assert (! "unexpected dynamic reloc type");
	134	break;
	135	}
	136	}
	137
a1a9d215 RM	138	static inline void
	139	elf_machine_lazy_rel (struct link_map map, const Elf32_Rel reloc)
	140	{
	141	Elf32_Addr const reloc_addr = (void ) (map->l_addr + reloc->r_offset);
	142	switch (ELF32_R_TYPE (reloc->r_info))
	143	{
	144	case R_386_JMP_SLOT:
	145	*reloc_addr += map->l_addr;
	146	break;
	147	default:
	148	assert (! "unexpected PLT reloc type");
	149	break;
	150	}
	151	}
d66e34cd	152
6c03c2cf RM	153	/* Nonzero iff TYPE describes relocation of a PLT entry, so
	154	PLT entries should not be allowed to define the value. */
	155	#define elf_machine_pltrel_p(type) ((type) == R_386_JMP_SLOT)
	156
d66e34cd	157	/* The i386 never uses Elf32_Rela relocations. */
421f82e5	158	#define ELF_MACHINE_NO_RELA 1
d66e34cd RM	159
	160
	161	/* Set up the loaded object described by L so its unrelocated PLT
	162	entries will jump to the on-demand fixup code in dl-runtime.c. */
	163
	164	static inline void
a2e1b046	165	elf_machine_runtime_setup (struct link_map *l, int lazy)
d66e34cd	166	{
a1a9d215	167	Elf32_Addr *got;
d66e34cd	168	extern void _dl_runtime_resolve (Elf32_Word);
a1a9d215	169
a2e1b046 RM	170	if (l->l_info[DT_JMPREL] && lazy)
	171	{
	172	/* The GOT entries for functions in the PLT have not yet been filled
	173	in. Their initial contents will arrange when called to push an
	174	offset into the .rel.plt section, push _GLOBAL_OFFSET_TABLE_[1],
	175	and then jump to _GLOBAL_OFFSET_TABLE[2]. */
	176	got = (Elf32_Addr *) (l->l_addr + l->l_info[DT_PLTGOT]->d_un.d_ptr);
	177	got[1] = (Elf32_Addr) l; /* Identify this shared object. */
	178	/* This function will get called to fix up the GOT entry indicated by
	179	the offset on the stack, and then jump to the resolved address. */
	180	got[2] = (Elf32_Addr) &_dl_runtime_resolve;
	181	}
d66e34cd	182
38334018 RM	183	/* This code is used in dl-runtime.c to call the `fixup' function
	184	and then redirect to the address it returns. */
	185	#define ELF_MACHINE_RUNTIME_TRAMPOLINE asm ("\
	186	.globl _dl_runtime_resolve
	187	.type _dl_runtime_resolve, @function
	188	_dl_runtime_resolve:
	189	call fixup # Args pushed by PLT.
	190	addl $8, %esp # Pop args.
	191	jmp *%eax # Jump to function address.
	192	");
	193	/* The PLT uses Elf32_Rel relocs. */
	194	#define elf_machine_relplt elf_machine_rel
	195	}
d66e34cd	196
5bf62f2d RM	197	/* Mask identifying addresses reserved for the user program,
	198	where the dynamic linker should not map anything. */
	199	#define ELF_MACHINE_USER_ADDRESS_MASK 0xf8000000UL
	200
	201
	202
d66e34cd RM	203	/* Initial entry point code for the dynamic linker.
	204	The C function `_dl_start' is the real entry point;
	205	its return value is the user program's entry point. */
	206
	207	#define RTLD_START asm ("\
	208	.text\n\
	209	.globl _start\n\
421f82e5 RM	210	.globl _dl_start_user\n\
	211	_start:\n\
	212	call _dl_start\n\
	213	_dl_start_user:\n\
	214	# Save the user entry point address in %edi.\n\
	215	movl %eax, %edi\n\
	216	# Point %ebx at the GOT.
a1a9d215 RM	217	call 0f\n\
	218	0: popl %ebx\n\
	219	addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ebx\n\
	220	# See if we were run as a command with the executable file\n\
	221	# name as an extra leading argument.\n\
24906b43	222	movl _dl_skip_args@GOT(%ebx), %eax\n\
a1a9d215	223	movl (%eax),%eax\n\
24906b43 RM	224	# Pop the original argument count.\n\
	225	popl %ecx\n\
	226	# Subtract _dl_skip_args from it.\n\
	227	subl %eax, %ecx\n\
	228	# Adjust the stack pointer to skip _dl_skip_args words.\n\
	229	leal (%esp,%eax,4), %esp\n\
	230	# Push back the modified argument count.\n\
	231	pushl %ecx\n\
f68b86cc RM	232	# Push _dl_loaded as argument in _dl_init_next call below.\n\
	233	movl _dl_loaded@GOT(%ebx), %eax\n\
	234	movl (%eax), %esi\n\
	235	0: pushl %esi\n\
d66e34cd RM	236	# Call _dl_init_next to return the address of an initializer\n\
d66e34cd RM	237	# function to run.\n\
f68b86cc RM	238	call _dl_init_next@PLT\n\
f68b86cc RM	239	addl $4, %esp # Pop argument.\n\
d66e34cd RM	240	# Check for zero return, when out of initializers.\n\
	241	testl %eax,%eax\n\
	242	jz 1f\n\
	243	# Call the shared object initializer function.\n\
f68b86cc	244	# NOTE: We depend only on the registers (%ebx, %esi and %edi)\n\
d66e34cd RM	245	# and the return address pushed by this call;\n\
	246	# the initializer is called with the stack just\n\
	247	# as it appears on entry, and it is free to move\n\
	248	# the stack around, as long as it winds up jumping to\n\
	249	# the return address on the top of the stack.\n\
	250	call *%eax\n\
	251	# Loop to call _dl_init_next for the next initializer.\n\
	252	jmp 0b\n\
a1a9d215 RM	253	1: # Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
a1a9d215 RM	254	movl _dl_fini@GOT(%ebx), %edx\n\
421f82e5 RM	255	# Jump to the user's entry point.\n\
421f82e5 RM	256	jmp *%edi\n\
d66e34cd	257	");