[PATCH 0/3] Simplify ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA and revert aarch64/arm's extern protected data handling
Fangrui Song
maskray@google.com
Sun May 1 06:06:12 GMT 2022
Say both a.so and b.so define protected var and the executable copy
relocates var. ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA has strange
semantics: a.so accesses the copy in the executable while b.so accesses
its own. This behavior requires that (a) the compiler emits
GOT-generating relocations (b) the linker produces GLOB_DAT instead of
RELATIVE.
Without the ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA code, b.so's GLOB_DAT
will bind to the executable (normal behavior).
For aarch64/arm it makes sense to restore the original behavior and don't
pay the ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA cost. The behavior is very
unlikely used by anyone.
* Clang code generation treats STV_PROTECTED the same way as STV_HIDDEN:
no GOT-generating relocation in the first place.
* gold and lld reject copy relocation on a STV_PROTECTED symbol.
* Nowadays -fpie/-fpic modes are popular. GCC/Clang's codegen uses
GOT-generating relocation when accessing an default visibility
external symbol which avoids copy relocation.
Fangrui Song (3):
elf: Remove ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA check for
non-DL_EXTERN_PROTECTED_DATA ports
Revert "[AArch64][BZ #17711] Fix extern protected data handling"
Revert "[ARM][BZ #17711] Fix extern protected data handling"
elf/dl-lookup.c | 46 ++++++++++++------------------------
sysdeps/aarch64/dl-machine.h | 13 +++++-----
sysdeps/aarch64/dl-sysdep.h | 2 --
sysdeps/arm/dl-machine.h | 10 +++-----
sysdeps/arm/dl-sysdep.h | 2 --
5 files changed, 24 insertions(+), 49 deletions(-)
--
2.36.0.464.gb9c8b46e94-goog
More information about the Libc-alpha
mailing list