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| author | Fangrui Song <maskray@google.com> | 2021-08-11 09:00:37 -0700 |
|---|---|---|
| committer | Fangrui Song <maskray@google.com> | 2021-08-11 09:00:38 -0700 |
| commit | 43d06ed218fc8be58987bdfd00e21e5720f0b862 (patch) | |
| tree | a0981530e58766ac0eaf0ce6c0ed3c41d24c1742 /sysdeps | |
| parent | 302247c89121e8d4c7629e589edbb4974fff6edb (diff) | |
| download | glibc-43d06ed218fc8be58987bdfd00e21e5720f0b862.tar.gz | |
aarch64: Make elf_machine_{load_address,dynamic} robust [BZ #28203]
The AArch64 ABI is largely platform agnostic and does not specify
_GLOBAL_OFFSET_TABLE_[0] ([1]). glibc ld.so turns out to be probably the
only user of _GLOBAL_OFFSET_TABLE_[0] and GNU ld defines the value
to the link-time address _DYNAMIC. [2]
In 2012, __ehdr_start was implemented in GNU ld and gold in binutils
2.23. Using adrp+add / (-mcmodel=tiny) adr to access
__ehdr_start/_DYNAMIC gives us a robust way to get the load address and
the link-time address of _DYNAMIC.
[1]: From a psABI maintainer, https://bugs.llvm.org/show_bug.cgi?id=49672#c2
[2]: LLD's aarch64 port does not set _GLOBAL_OFFSET_TABLE_[0] to the
link-time address _DYNAMIC.
LLD is widely used on aarch64 Android and ChromeOS devices. Software
just works without the need for _GLOBAL_OFFSET_TABLE_[0].
Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
Diffstat (limited to 'sysdeps')
| -rw-r--r-- | sysdeps/aarch64/dl-machine.h | 24 |
1 files changed, 9 insertions, 15 deletions
diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h index d29d827ab3..3e10cb462f 100644 --- a/sysdeps/aarch64/dl-machine.h +++ b/sysdeps/aarch64/dl-machine.h @@ -37,28 +37,22 @@ elf_machine_matches_host (const ElfW(Ehdr) *ehdr) return ehdr->e_machine == EM_AARCH64; } -/* Return the link-time address of _DYNAMIC. Conveniently, this is the - first element of the GOT. */ -static inline ElfW(Addr) __attribute__ ((unused)) -elf_machine_dynamic (void) -{ - extern const ElfW(Addr) _GLOBAL_OFFSET_TABLE_[] attribute_hidden; - return _GLOBAL_OFFSET_TABLE_[0]; -} - /* Return the run-time load address of the shared object. */ static inline ElfW(Addr) __attribute__ ((unused)) elf_machine_load_address (void) { - /* To figure out the load address we use the definition that for any symbol: - dynamic_addr(symbol) = static_addr(symbol) + load_addr + extern const ElfW(Ehdr) __ehdr_start attribute_hidden; + return (ElfW(Addr)) &__ehdr_start; +} - _DYNAMIC sysmbol is used here as its link-time address stored in - the special unrelocated first GOT entry. */ +/* Return the link-time address of _DYNAMIC. */ - extern ElfW(Dyn) _DYNAMIC[] attribute_hidden; - return (ElfW(Addr)) &_DYNAMIC - elf_machine_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 |