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llvm-svn: 248894
This commit is contained in:
Rafael Espindola
2015-09-30 12:30:58 +00:00
parent 33cb9f9419
commit 3c412e14cc
1 changed files with 16 additions and 8 deletions
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24
lld/ELF/Target.cpp
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@@ -111,21 +111,29 @@ bool X86_64TargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
return false;
case R_X86_64_PC32:
// This relocation is defined to have a value of (S + A - P).
// The problems start when a non PIC program calls a function is a shared
// The problems start when a non PIC program calls a function in a shared
// library.
// In an ideal world, we could just report an error saying the relocation
// can overflow at runtime.
// In the real world, crt1.o has a R_X86_64_PC32 pointing to libc.so.
// The general idea is to create a PLT entry and use that as the function
// value, which is why we return true in here.
// In the real world with glibc, crt1.o has a R_X86_64_PC32 pointing to
// libc.so.
//
// The general idea on how to handle such cases is to create a PLT entry
// and use that as the function value.
//
// For the static linking part, we just return true and everything else
// will use the the PLT entry as the address.
//
// The remaining (unimplemented) problem is making sure pointer equality
// still works. For that, we need the help of the dynamic linker. We
// let it know that we have a direct reference to a symbol by creating
// an undefined symbol with a non zero st_value. Seeing that the
// still works. We need the help of the dynamic linker for that. We
// let it know that we have a direct reference to a so symbol by creating
// an undefined symbol with a non zero st_value. Seeing that, the
// dynamic linker resolves the symbol to the value of the symbol we created.
// This is true even for got entries, so pointer equality is maintained.
// To avoid an infinite loop, the only entry that points to the
// real function is a dedicated got entry used by the plt.
// real function is a dedicated got entry used by the plt. That is
// identified by special relocation types (R_X86_64_JUMP_SLOT,
// R_386_JMP_SLOT, etc).
return S.isShared();
case R_X86_64_PLT32:
return true;