glibc/sysdeps/i386/dl-machine.h

/* Machine-dependent ELF dynamic relocation inline functions.  i386 version.
   Copyright (C) 1995-2023 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 Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef dl_machine_h
#define dl_machine_h

#define ELF_MACHINE_NAME "i386"

#include <assert.h>
#include <sys/param.h>
#include <sysdep.h>
#include <tls.h>
#include <dl-tlsdesc.h>
#include <dl-static-tls.h>
#include <dl-machine-rel.h>

/* Return nonzero iff ELF header is compatible with the running host.  */
static inline int __attribute__ ((unused))
elf_machine_matches_host (const Elf32_Ehdr *ehdr)
{
  return ehdr->e_machine == EM_386;
}


/* Return the run-time load address of the shared object.  */
static inline Elf32_Addr __attribute__ ((unused))
elf_machine_load_address (void)
{
  extern const Elf32_Ehdr __ehdr_start attribute_hidden;
  return (Elf32_Addr) &__ehdr_start;
}

/* Return the link-time address of _DYNAMIC.  */
static inline Elf32_Addr __attribute__ ((unused))
elf_machine_dynamic (void)
{
  extern Elf32_Dyn _DYNAMIC[] attribute_hidden;
  return (Elf32_Addr) _DYNAMIC - elf_machine_load_address ();
}

/* 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 __attribute__ ((unused, always_inline))
elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
			   int lazy, int profile)
{
  Elf32_Addr *got;
  extern void _dl_runtime_resolve (Elf32_Word) attribute_hidden;
  extern void _dl_runtime_profile (Elf32_Word) attribute_hidden;
  extern void _dl_runtime_resolve_shstk (Elf32_Word) attribute_hidden;
  extern void _dl_runtime_profile_shstk (Elf32_Word) attribute_hidden;
  /* Check if SHSTK is enabled by kernel.  */
  bool shstk_enabled
    = (GL(dl_x86_feature_1) & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;

  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 *) D_PTR (l, l_info[DT_PLTGOT]);
      /* If a library is prelinked but we have to relocate anyway,
	 we have to be able to undo the prelinking of .got.plt.
	 The prelinker saved us here address of .plt + 0x16.  */
      if (got[1])
	{
	  l->l_mach.plt = got[1] + l->l_addr;
	  l->l_mach.gotplt = (Elf32_Addr) &got[3];
	}
      got[1] = (Elf32_Addr) l;	/* Identify this shared object.  */

      /* The got[2] entry contains the address of a function which gets
	 called to get the address of a so far unresolved function and
	 jump to it.  The profiling extension of the dynamic linker allows
	 to intercept the calls to collect information.  In this case we
	 don't store the address in the GOT so that all future calls also
	 end in this function.  */
      if (__glibc_unlikely (profile))
	{
	  got[2] = (shstk_enabled
		    ? (Elf32_Addr) &_dl_runtime_profile_shstk
		    : (Elf32_Addr) &_dl_runtime_profile);

	  if (GLRO(dl_profile) != NULL
	      && _dl_name_match_p (GLRO(dl_profile), l))
	    /* This is the object we are looking for.  Say that we really
	       want profiling and the timers are started.  */
	    GL(dl_profile_map) = l;
	}
      else
	/* 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] = (shstk_enabled
		  ? (Elf32_Addr) &_dl_runtime_resolve_shstk
		  : (Elf32_Addr) &_dl_runtime_resolve);
    }

  return lazy;
}

/* 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 ("\n\
	.text\n\
	.align 16\n\
0:	movl (%esp), %ebx\n\
	ret\n\
	.align 16\n\
.globl _start\n\
.globl _dl_start_user\n\
_start:\n\
	movl %esp, %eax\n\
        subl $12, %esp\n\
        pushl %eax\n\
	call _dl_start\n\
        addl $16, %esp\n\
_dl_start_user:\n\
	# Save the user entry point address in %edi.\n\
	movl %eax, %edi\n\
	# Point %ebx at the GOT.\n\
	call 0b\n\
	addl $_GLOBAL_OFFSET_TABLE_, %ebx\n\
	# Read the original argument count.\n\
	movl (%esp), %edx\n\
	# The special initializer gets called with the stack just\n\
	# as the application's entry point will see it; it can\n\
	# switch stacks if it moves these contents over.\n\
" RTLD_START_SPECIAL_INIT "\n\
	# Load the parameters again.\n\
	# (eax, edx, ecx, esi) = (_dl_loaded, argc, argv, envp)\n\
	movl _rtld_local@GOTOFF(%ebx), %eax\n\
	leal 8(%esp,%edx,4), %esi\n\
	leal 4(%esp), %ecx\n\
	movl %esp, %ebp\n\
	# Make sure _dl_init is run with 16 byte aligned stack.\n\
	andl $-16, %esp\n\
        subl $12, %esp\n\
	pushl %ebp\n\
        # Arguments for _dl_init.\n\
	pushl %esi\n\
	pushl %ecx\n\
	pushl %edx\n\
	pushl %eax\n\
	# Clear %ebp, so that even constructors have terminated backchain.\n\
	xorl %ebp, %ebp\n\
	# Call the function to run the initializers.\n\
	call _dl_init\n\
	# Pass our finalizer function to the user in %edx, as per ELF ABI.\n\
	leal _dl_fini@GOTOFF(%ebx), %edx\n\
	# Restore %esp _start expects.\n\
	movl 16(%esp), %esp\n\
	# Jump to the user's entry point.\n\
	jmp *%edi\n\
	.previous\n\
");

#ifndef RTLD_START_SPECIAL_INIT
# define RTLD_START_SPECIAL_INIT /* nothing */
#endif

/* ELF_RTYPE_CLASS_PLT iff TYPE describes relocation of a PLT entry or
   TLS variable, so undefined references should not be allowed to
   define the value.
   ELF_RTYPE_CLASS_COPY iff TYPE should not be allowed to resolve to one
   of the main executable's symbols, as for a COPY reloc.  */
# define elf_machine_type_class(type) \
  ((((type) == R_386_JMP_SLOT || (type) == R_386_TLS_DTPMOD32		      \
     || (type) == R_386_TLS_DTPOFF32 || (type) == R_386_TLS_TPOFF32	      \
     || (type) == R_386_TLS_TPOFF || (type) == R_386_TLS_DESC)		      \
    * ELF_RTYPE_CLASS_PLT)						      \
   | (((type) == R_386_COPY) * ELF_RTYPE_CLASS_COPY))

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

/* We define an initialization functions.  This is called very early in
   _dl_sysdep_start.  */
#define DL_PLATFORM_INIT dl_platform_init ()

static inline void __attribute__ ((unused))
dl_platform_init (void)
{
#if IS_IN (rtld)
  /* _dl_x86_init_cpu_features is a wrapper for init_cpu_features which
     has been called early from __libc_start_main in static executable.  */
  _dl_x86_init_cpu_features ();
#else
  if (GLRO(dl_platform) != NULL && *GLRO(dl_platform) == '\0')
    /* Avoid an empty string which would disturb us.  */
    GLRO(dl_platform) = NULL;
#endif
}

static inline Elf32_Addr
elf_machine_fixup_plt (struct link_map *map, lookup_t t,
		       const ElfW(Sym) *refsym, const ElfW(Sym) *sym,
		       const Elf32_Rel *reloc,
		       Elf32_Addr *reloc_addr, Elf32_Addr value)
{
  return *reloc_addr = value;
}

/* Return the final value of a plt relocation.  */
static inline Elf32_Addr
elf_machine_plt_value (struct link_map *map, const Elf32_Rel *reloc,
		       Elf32_Addr value)
{
  return value;
}


/* Names of the architecture-specific auditing callback functions.  */
#define ARCH_LA_PLTENTER i86_gnu_pltenter
#define ARCH_LA_PLTEXIT i86_gnu_pltexit

#endif /* !dl_machine_h */

#ifdef RESOLVE_MAP

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

static inline void
__attribute ((always_inline))
elf_machine_rel (struct link_map *map, struct r_scope_elem *scope[],
		 const Elf32_Rel *reloc,
		 const Elf32_Sym *sym, const struct r_found_version *version,
		 void *const reloc_addr_arg, int skip_ifunc)
{
  Elf32_Addr *const reloc_addr = reloc_addr_arg;
  const unsigned int r_type = ELF32_R_TYPE (reloc->r_info);

# if !defined RTLD_BOOTSTRAP
  if (__glibc_unlikely (r_type == R_386_RELATIVE))
    *reloc_addr += map->l_addr;
#  ifndef RTLD_BOOTSTRAP
  else if (__glibc_unlikely (r_type == R_386_NONE))
    return;
#  endif
  else
# endif	/* !RTLD_BOOTSTRAP */
    {
# ifndef RTLD_BOOTSTRAP
      const Elf32_Sym *const refsym = sym;
# endif
      struct link_map *sym_map = RESOLVE_MAP (map, scope, &sym, version,
					      r_type);
      Elf32_Addr value = SYMBOL_ADDRESS (sym_map, sym, true);

      if (sym != NULL
	  && __glibc_unlikely (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC)
	  && __glibc_likely (sym->st_shndx != SHN_UNDEF)
	  && __glibc_likely (!skip_ifunc))
	{
# ifndef RTLD_BOOTSTRAP
	  if (sym_map != map
	      && !sym_map->l_relocated)
	    {
	      const char *strtab
		= (const char *) D_PTR (map, l_info[DT_STRTAB]);
	      if (sym_map->l_type == lt_executable)
		_dl_fatal_printf ("\
%s: IFUNC symbol '%s' referenced in '%s' is defined in the executable \
and creates an unsatisfiable circular dependency.\n",
				  RTLD_PROGNAME, strtab + refsym->st_name,
				  map->l_name);
	      else
		_dl_error_printf ("\
%s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
				  RTLD_PROGNAME, map->l_name,
				  sym_map->l_name,
				  strtab + refsym->st_name);
	    }
# endif
	  value = ((Elf32_Addr (*) (void)) value) ();
	}

      switch (r_type)
	{
# ifndef RTLD_BOOTSTRAP
	case R_386_SIZE32:
	  /* Set to symbol size plus addend.  */
	  *reloc_addr += sym->st_size;
	  break;
# endif
	case R_386_GLOB_DAT:
	case R_386_JMP_SLOT:
	  *reloc_addr = value;
	  break;

	case R_386_TLS_DTPMOD32:
# ifdef RTLD_BOOTSTRAP
	  /* During startup the dynamic linker is always the module
	     with index 1.
	     XXX If this relocation is necessary move before RESOLVE
	     call.  */
	  *reloc_addr = 1;
# else
	  /* Get the information from the link map returned by the
	     resolv function.  */
	  if (sym_map != NULL)
	    *reloc_addr = sym_map->l_tls_modid;
# endif
	  break;
	case R_386_TLS_DTPOFF32:
# ifndef RTLD_BOOTSTRAP
	  /* During relocation all TLS symbols are defined and used.
	     Therefore the offset is already correct.  */
	  if (sym != NULL)
	    *reloc_addr = sym->st_value;
# endif
	  break;
	case R_386_TLS_DESC:
	  {
	    struct tlsdesc volatile *td =
	      (struct tlsdesc volatile *)reloc_addr;

# ifndef RTLD_BOOTSTRAP
	    if (! sym)
	      td->entry = _dl_tlsdesc_undefweak;
	    else
# endif
	      {
# ifndef RTLD_BOOTSTRAP
#  ifndef SHARED
		CHECK_STATIC_TLS (map, sym_map);
#  else
		if (!TRY_STATIC_TLS (map, sym_map))
		  {
		    td->arg = _dl_make_tlsdesc_dynamic
		      (sym_map, sym->st_value + (ElfW(Word))td->arg);
		    td->entry = _dl_tlsdesc_dynamic;
		  }
		else
#  endif
# endif
		  {
		    td->arg = (void*)(sym->st_value - sym_map->l_tls_offset
				      + (ElfW(Word))td->arg);
		    td->entry = _dl_tlsdesc_return;
		  }
	      }
	    break;
	  }
	case R_386_TLS_TPOFF32:
	  /* The offset is positive, backward from the thread pointer.  */
#  ifdef RTLD_BOOTSTRAP
	  *reloc_addr += map->l_tls_offset - sym->st_value;
#  else
	  /* We know the offset of object the symbol is contained in.
	     It is a positive value which will be subtracted from the
	     thread pointer.  To get the variable position in the TLS
	     block we subtract the offset from that of the TLS block.  */
	  if (sym != NULL)
	    {
	      CHECK_STATIC_TLS (map, sym_map);
	      *reloc_addr += sym_map->l_tls_offset - sym->st_value;
	    }
# endif
	  break;
	case R_386_TLS_TPOFF:
	  /* The offset is negative, forward from the thread pointer.  */
# ifdef RTLD_BOOTSTRAP
	  *reloc_addr += sym->st_value - map->l_tls_offset;
# else
	  /* We know the offset of object the symbol is contained in.
	     It is a negative value which will be added to the
	     thread pointer.  */
	  if (sym != NULL)
	    {
	      CHECK_STATIC_TLS (map, sym_map);
	      *reloc_addr += sym->st_value - sym_map->l_tls_offset;
	    }
# endif
	  break;

# ifndef RTLD_BOOTSTRAP
	case R_386_32:
	  *reloc_addr += value;
	  break;
	case R_386_PC32:
	  *reloc_addr += (value - (Elf32_Addr) reloc_addr);
	  break;
	case R_386_COPY:
	  if (sym == NULL)
	    /* This can happen in trace mode if an object could not be
	       found.  */
	    break;
	  if (__glibc_unlikely (sym->st_size > refsym->st_size)
	      || (__glibc_unlikely(sym->st_size < refsym->st_size)
		  && GLRO(dl_verbose)))
	    {
	      const char *strtab;

	      strtab = (const char *) D_PTR (map, l_info[DT_STRTAB]);
	      _dl_error_printf ("\
%s: Symbol `%s' has different size in shared object, consider re-linking\n",
				RTLD_PROGNAME, strtab + refsym->st_name);
	    }
	  memcpy (reloc_addr_arg, (void *) value,
		  MIN (sym->st_size, refsym->st_size));
	  break;
	case R_386_IRELATIVE:
	  value = map->l_addr + *reloc_addr;
	  if (__glibc_likely (!skip_ifunc))
	    value = ((Elf32_Addr (*) (void)) value) ();
	  *reloc_addr = value;
	  break;
	default:
	  _dl_reloc_bad_type (map, r_type, 0);
	  break;
# endif	/* !RTLD_BOOTSTRAP */
	}
    }
}


static inline void
__attribute ((always_inline))
elf_machine_rel_relative (Elf32_Addr l_addr, const Elf32_Rel *reloc,
			  void *const reloc_addr_arg)
{
  Elf32_Addr *const reloc_addr = reloc_addr_arg;
  assert (ELF32_R_TYPE (reloc->r_info) == R_386_RELATIVE);
  *reloc_addr += l_addr;
}

# ifndef RTLD_BOOTSTRAP
static inline void
__attribute__ ((always_inline))
elf_machine_rela_relative (Elf32_Addr l_addr, const Elf32_Rela *reloc,
			   void *const reloc_addr_arg)
{
  Elf32_Addr *const reloc_addr = reloc_addr_arg;
  *reloc_addr = l_addr + reloc->r_addend;
}
# endif	/* !RTLD_BOOTSTRAP */

static inline void
__attribute__ ((always_inline))
elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
		      Elf32_Addr l_addr, const Elf32_Rel *reloc,
		      int skip_ifunc)
{
  Elf32_Addr *const reloc_addr = (void *) (l_addr + reloc->r_offset);
  const unsigned int r_type = ELF32_R_TYPE (reloc->r_info);
  /* Check for unexpected PLT reloc type.  */
  if (__glibc_likely (r_type == R_386_JMP_SLOT))
    {
      /* Prelink has been deprecated.  */
      if (__glibc_likely (map->l_mach.plt == 0))
	*reloc_addr += l_addr;
      else
	*reloc_addr = (map->l_mach.plt
		       + (((Elf32_Addr) reloc_addr) - map->l_mach.gotplt) * 4);
    }
  else if (__glibc_likely (r_type == R_386_TLS_DESC))
    {
      const Elf32_Rel *const r = reloc;
      /* The code below was borrowed from elf_dynamic_do_rel().  */
      const ElfW(Sym) *const symtab =
	(const void *) D_PTR (map, l_info[DT_SYMTAB]);

      /* Always initialize TLS descriptors completely at load time, in
	 case static TLS is allocated for it that requires locking.  */
# ifdef RTLD_BOOTSTRAP
      /* The dynamic linker always uses versioning.  */
      assert (map->l_info[VERSYMIDX (DT_VERSYM)] != NULL);
# else
      if (map->l_info[VERSYMIDX (DT_VERSYM)])
# endif
	{
	  const ElfW(Half) *const version =
	    (const void *) D_PTR (map, l_info[VERSYMIDX (DT_VERSYM)]);
	  ElfW(Half) ndx = version[ELFW(R_SYM) (r->r_info)] & 0x7fff;
	  elf_machine_rel (map, scope, r, &symtab[ELFW(R_SYM) (r->r_info)],
			   &map->l_versions[ndx],
			   (void *) (l_addr + r->r_offset), skip_ifunc);
	}
# ifndef RTLD_BOOTSTRAP
      else
	elf_machine_rel (map, scope, r, &symtab[ELFW(R_SYM) (r->r_info)], NULL,
			 (void *) (l_addr + r->r_offset), skip_ifunc);
# endif
    }
  else if (__glibc_unlikely (r_type == R_386_IRELATIVE))
    {
      Elf32_Addr value = map->l_addr + *reloc_addr;
      if (__glibc_likely (!skip_ifunc))
	value = ((Elf32_Addr (*) (void)) value) ();
      *reloc_addr = value;
    }
  else
    _dl_reloc_bad_type (map, r_type, 1);
}

#endif /* RESOLVE_MAP */