diff options
Diffstat (limited to 'lld/ELF/Target.cpp')
| -rw-r--r-- | lld/ELF/Target.cpp | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/lld/ELF/Target.cpp b/lld/ELF/Target.cpp index a68cf8b80b2..df2e7e6fcea 100644 --- a/lld/ELF/Target.cpp +++ b/lld/ELF/Target.cpp @@ -74,6 +74,9 @@ public: void relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type, uint64_t P, uint64_t SA) const override; bool isRelRelative(uint32_t Type) const override; + bool isTlsOptimized(unsigned Type, const SymbolBody &S) const override; + void relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd, uint64_t P, + uint64_t SA) const override; }; class PPC64TargetInfo final : public TargetInfo { @@ -148,6 +151,10 @@ TargetInfo *createTarget() { TargetInfo::~TargetInfo() {} +bool TargetInfo::isTlsOptimized(unsigned Type, const SymbolBody &S) const { + return false; +} + uint64_t TargetInfo::getVAStart() const { return Config->Shared ? 0 : VAStart; } bool TargetInfo::relocNeedsCopy(uint32_t Type, const SymbolBody &S) const { @@ -162,6 +169,9 @@ bool TargetInfo::relocPointsToGot(uint32_t Type) const { return false; } bool TargetInfo::isRelRelative(uint32_t Type) const { return true; } +void TargetInfo::relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd, uint64_t P, + uint64_t SA) const {} + void TargetInfo::writeGotHeaderEntries(uint8_t *Buf) const {} void TargetInfo::writeGotPltHeaderEntries(uint8_t *Buf) const {} @@ -279,6 +289,8 @@ bool X86_64TargetInfo::relocNeedsCopy(uint32_t Type, } bool X86_64TargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const { + if (Type == R_X86_64_GOTTPOFF) + return !isTlsOptimized(Type, S); return Type == R_X86_64_GOTTPOFF || Type == R_X86_64_GOTPCREL || relocNeedsPlt(Type, S); } @@ -344,6 +356,48 @@ bool X86_64TargetInfo::isRelRelative(uint32_t Type) const { } } +bool X86_64TargetInfo::isTlsOptimized(unsigned Type, + const SymbolBody &S) const { + if (Config->Shared || !S.isTLS()) + return false; + return Type == R_X86_64_GOTTPOFF && !canBePreempted(&S, true); +} + +// In some conditions, R_X86_64_GOTTPOFF relocation can be optimized to +// R_X86_64_TPOFF32 so that R_X86_64_TPOFF32 so that it does not use GOT. +// This function does that. Read "ELF Handling For Thread-Local Storage, +// 5.5 x86-x64 linker optimizations" (http://www.akkadia.org/drepper/tls.pdf) +// by Ulrich Drepper for details. +void X86_64TargetInfo::relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd, + uint64_t P, uint64_t SA) const { + // Ulrich's document section 6.5 says that @gottpoff(%rip) must be + // used in MOVQ or ADDQ instructions only. + // "MOVQ foo@GOTTPOFF(%RIP), %REG" is transformed to "MOVQ $foo, %REG". + // "ADDQ foo@GOTTPOFF(%RIP), %REG" is transformed to "LEAQ foo(%REG), %REG" + // (if the register is not RSP/R12) or "ADDQ $foo, %RSP". + // Opcodes info can be found at http://ref.x86asm.net/coder64.html#x48. + uint8_t *Prefix = Loc - 3; + uint8_t *Inst = Loc - 2; + uint8_t *RegSlot = Loc - 1; + uint8_t Reg = Loc[-1] >> 3; + bool IsMov = *Inst == 0x8b; + bool RspAdd = !IsMov && Reg == 4; + // r12 and rsp registers requires special handling. + // Problem is that for other registers, for example leaq 0xXXXXXXXX(%r11),%r11 + // result out is 7 bytes: 4d 8d 9b XX XX XX XX, + // but leaq 0xXXXXXXXX(%r12),%r12 is 8 bytes: 4d 8d a4 24 XX XX XX XX. + // The same true for rsp. So we convert to addq for them, saving 1 byte that + // we dont have. + if (RspAdd) + *Inst = 0x81; + else + *Inst = IsMov ? 0xc7 : 0x8d; + if (*Prefix == 0x4c) + *Prefix = (IsMov || RspAdd) ? 0x49 : 0x4d; + *RegSlot = (IsMov || RspAdd) ? (0xc0 | Reg) : (0x80 | Reg | (Reg << 3)); + relocateOne(Loc, BufEnd, R_X86_64_TPOFF32, P, SA); +} + void X86_64TargetInfo::relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type, uint64_t P, uint64_t SA) const { switch (Type) { |
