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19a6a3acd1
IFUNC is difficult to correctly implement on any target needing a GOT to support position independent code, due to the dependency on order of dynamic relocations. ld.so should be changed to apply IFUNC relocations last, globally, because without that it is actually impossible to write an IFUNC resolver in C that works in all situations. Case in point, vfork in libpthread.so is an IFUNC with the resolver returning &__libc_vfork. (system and fork are similar.) If another shared library, libA say, uses vfork then it is quite possible that libpthread.so hasn't been dynamically relocated before the unfortunate libA is dynamically relocated. In that case the GOT entry for &__libc_vfork is still zero, so the IFUNC resolver returns NULL. LD_BIND_NOW=1 results in libA PLT dynamic relocations being applied using this NULL value and ld.so segfaults. This patch hardens ld.so to not segfault on a NULL from an IFUNC resolver. It also fixes a problem with undefined weak. If you leave the plt entry as-is for undefined weak then if the entry is ever called it will loop in ld.so rather than segfaulting. * sysdeps/powerpc/powerpc64/dl-machine.h (elf_machine_fixup_plt): Don't segfault if ifunc resolver returns a NULL. Do set plt to zero for undefined weak. (elf_machine_plt_conflict): Similarly. |
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