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Kernel: Introduce workaround to make LTO builds work with Clang

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LLD fails to define the _GLOBAL_OFFSET_TABLE_ symbol if all inputs to it
are LLVM bitcode files (i.e. those used for LTO). To allow the kernel to
be built with ThinLTO, the workaround suggested in the original LLVM bug
report (<https://bugs.llvm.org/show_bug.cgi?id=39634>) is added in this
commit.
This commit is contained in:
Daniel Bertalan 2021-10-09 19:05:19 +02:00 • committed by Linus Groh
parent 3c3df95958
commit 1faffc2192
2 changed files with 13 additions and 0 deletions
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12
Kernel/StdLib.cpp
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@ -207,6 +207,18 @@ KResult memset_user(void* dest_ptr, int c, size_t n)
return KSuccess;
}
#if defined(__clang__) && defined(ENABLE_KERNEL_LTO)
// Due to a chicken-and-egg situation, certain linker-defined symbols that are added on-demand (like the GOT)
// need to be present before LTO bitcode files are compiled. And since we don't link to any native object files,
// the linker does not know that _GLOBAL_OFFSET_TABLE_ is needed, so it doesn't define it, so linking as a PIE fails.
// See https://bugs.llvm.org/show_bug.cgi?id=39634
FlatPtr missing_got_workaround()
{
extern volatile FlatPtr _GLOBAL_OFFSET_TABLE_;
return _GLOBAL_OFFSET_TABLE_;
}
#endif
extern "C" {
const void* memmem(const void* haystack, size_t haystack_length, const void* needle, size_t needle_length)