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arm: Simplify elf_machine_{load_address,dynamic}

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and drop reliance on _GLOBAL_OFFSET_TABLE_[0] being the link-time
address of _DYNAMIC. &__ehdr_start is a better way to get the load address.

This is similar to commits b37b75d269883a2c553bb7019a813094eb4e2dd1
(x86-64) and 43d06ed218fc8be58987bdfd00e21e5720f0b862 (aarch64).

Reviewed-by: Joseph Myers <joseph@codesourcery.com>
This commit is contained in:
Fangrui Song 2021-08-18 11:13:03 -07:00
parent 34b4624b04
commit bca0f5cbc9
1 changed files with 10 additions and 37 deletions

47
sysdeps/arm/dl-machine.h

@ -37,48 +37,21 @@ elf_machine_matches_host (const Elf32_Ehdr *ehdr)
return ehdr->e_machine == EM_ARM;
}
/* Return the link-time address of _DYNAMIC. Conveniently, this is the
first element of the GOT. */
static inline Elf32_Addr __attribute__ ((unused))
elf_machine_dynamic (void)
{
/* Declaring this hidden ensures that a PC-relative reference is used. */
extern const Elf32_Addr _GLOBAL_OFFSET_TABLE_[] attribute_hidden;
return _GLOBAL_OFFSET_TABLE_[0];
}
/* Return the run-time load address of the shared object. */
static inline Elf32_Addr __attribute__ ((unused))
static inline ElfW(Addr) __attribute__ ((unused))
elf_machine_load_address (void)
{
Elf32_Addr pcrel_addr;
#ifdef SHARED
extern Elf32_Addr __dl_start (void *) asm ("_dl_start");
Elf32_Addr got_addr = (Elf32_Addr) &__dl_start;
asm ("adr %0, _dl_start" : "=r" (pcrel_addr));
#else
extern Elf32_Addr __dl_relocate_static_pie (void *)
asm ("_dl_relocate_static_pie") attribute_hidden;
Elf32_Addr got_addr = (Elf32_Addr) &__dl_relocate_static_pie;
asm ("adr %0, _dl_relocate_static_pie" : "=r" (pcrel_addr));
#endif
#ifdef __thumb__
/* Clear the low bit of the function address.
NOTE: got_addr is from GOT table whose lsb is always set by linker if it's
Thumb function address. PCREL_ADDR comes from PC-relative calculation
which will finish during assembling. GAS assembler before the fix for
PR gas/21458 was not setting the lsb but does after that. Always do the
strip for both, so the code works with various combinations of glibc and
Binutils. */
got_addr &= ~(Elf32_Addr) 1;
pcrel_addr &= ~(Elf32_Addr) 1;
#endif
return pcrel_addr - got_addr;
extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
return (ElfW(Addr)) &__ehdr_start;
}
/* Return the link-time address of _DYNAMIC. */
static inline ElfW(Addr) __attribute__ ((unused))
elf_machine_dynamic (void)
{
extern ElfW(Dyn) _DYNAMIC[] attribute_hidden;
return (ElfW(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. */