| //===- X86.cpp ------------------------------------------------------------===// |
| // |
| // The LLVM Linker |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "InputFiles.h" |
| #include "Symbols.h" |
| #include "SyntheticSections.h" |
| #include "Target.h" |
| #include "lld/Common/ErrorHandler.h" |
| #include "llvm/Support/Endian.h" |
| |
| using namespace llvm; |
| using namespace llvm::support::endian; |
| using namespace llvm::ELF; |
| using namespace lld; |
| using namespace lld::elf; |
| |
| namespace { |
| class X86 : public TargetInfo { |
| public: |
| X86(); |
| RelExpr getRelExpr(RelType Type, const Symbol &S, |
| const uint8_t *Loc) const override; |
| int64_t getImplicitAddend(const uint8_t *Buf, RelType Type) const override; |
| void writeGotPltHeader(uint8_t *Buf) const override; |
| RelType getDynRel(RelType Type) const override; |
| void writeGotPlt(uint8_t *Buf, const Symbol &S) const override; |
| void writeIgotPlt(uint8_t *Buf, const Symbol &S) const override; |
| void writePltHeader(uint8_t *Buf) const override; |
| void writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, uint64_t PltEntryAddr, |
| int32_t Index, unsigned RelOff) const override; |
| void relocateOne(uint8_t *Loc, RelType Type, uint64_t Val) const override; |
| |
| RelExpr adjustRelaxExpr(RelType Type, const uint8_t *Data, |
| RelExpr Expr) const override; |
| void relaxTlsGdToIe(uint8_t *Loc, RelType Type, uint64_t Val) const override; |
| void relaxTlsGdToLe(uint8_t *Loc, RelType Type, uint64_t Val) const override; |
| void relaxTlsIeToLe(uint8_t *Loc, RelType Type, uint64_t Val) const override; |
| void relaxTlsLdToLe(uint8_t *Loc, RelType Type, uint64_t Val) const override; |
| }; |
| } // namespace |
| |
| X86::X86() { |
| CopyRel = R_386_COPY; |
| GotRel = R_386_GLOB_DAT; |
| PltRel = R_386_JUMP_SLOT; |
| IRelativeRel = R_386_IRELATIVE; |
| RelativeRel = R_386_RELATIVE; |
| TlsGotRel = R_386_TLS_TPOFF; |
| TlsModuleIndexRel = R_386_TLS_DTPMOD32; |
| TlsOffsetRel = R_386_TLS_DTPOFF32; |
| GotEntrySize = 4; |
| GotPltEntrySize = 4; |
| PltEntrySize = 16; |
| PltHeaderSize = 16; |
| TlsGdRelaxSkip = 2; |
| TrapInstr = 0xcccccccc; // 0xcc = INT3 |
| } |
| |
| static bool hasBaseReg(uint8_t ModRM) { return (ModRM & 0xc7) != 0x5; } |
| |
| RelExpr X86::getRelExpr(RelType Type, const Symbol &S, |
| const uint8_t *Loc) const { |
| switch (Type) { |
| case R_386_8: |
| case R_386_16: |
| case R_386_32: |
| case R_386_TLS_LDO_32: |
| return R_ABS; |
| case R_386_TLS_GD: |
| return R_TLSGD_GOT_FROM_END; |
| case R_386_TLS_LDM: |
| return R_TLSLD_GOT_FROM_END; |
| case R_386_PLT32: |
| return R_PLT_PC; |
| case R_386_PC8: |
| case R_386_PC16: |
| case R_386_PC32: |
| return R_PC; |
| case R_386_GOTPC: |
| return R_GOTONLY_PC_FROM_END; |
| case R_386_TLS_IE: |
| return R_GOT; |
| case R_386_GOT32: |
| case R_386_GOT32X: |
| // These relocations are arguably mis-designed because their calculations |
| // depend on the instructions they are applied to. This is bad because we |
| // usually don't care about whether the target section contains valid |
| // machine instructions or not. But this is part of the documented ABI, so |
| // we had to implement as the standard requires. |
| // |
| // x86 does not support PC-relative data access. Therefore, in order to |
| // access GOT contents, a GOT address needs to be known at link-time |
| // (which means non-PIC) or compilers have to emit code to get a GOT |
| // address at runtime (which means code is position-independent but |
| // compilers need to emit extra code for each GOT access.) This decision |
| // is made at compile-time. In the latter case, compilers emit code to |
| // load an GOT address to a register, which is usually %ebx. |
| // |
| // So, there are two ways to refer to symbol foo's GOT entry: foo@GOT or |
| // foo@GOT(%reg). |
| // |
| // foo@GOT is not usable in PIC. If we are creating a PIC output and if we |
| // find such relocation, we should report an error. foo@GOT is resolved to |
| // an *absolute* address of foo's GOT entry, because both GOT address and |
| // foo's offset are known. In other words, it's G + A. |
| // |
| // foo@GOT(%reg) needs to be resolved to a *relative* offset from a GOT to |
| // foo's GOT entry in the table, because GOT address is not known but foo's |
| // offset in the table is known. It's G + A - GOT. |
| // |
| // It's unfortunate that compilers emit the same relocation for these |
| // different use cases. In order to distinguish them, we have to read a |
| // machine instruction. |
| // |
| // The following code implements it. We assume that Loc[0] is the first |
| // byte of a displacement or an immediate field of a valid machine |
| // instruction. That means a ModRM byte is at Loc[-1]. By taking a look at |
| // the byte, we can determine whether the instruction is register-relative |
| // (i.e. it was generated for foo@GOT(%reg)) or absolute (i.e. foo@GOT). |
| return hasBaseReg(Loc[-1]) ? R_GOT_FROM_END : R_GOT; |
| case R_386_TLS_GOTIE: |
| return R_GOT_FROM_END; |
| case R_386_GOTOFF: |
| return R_GOTREL_FROM_END; |
| case R_386_TLS_LE: |
| return R_TLS; |
| case R_386_TLS_LE_32: |
| return R_NEG_TLS; |
| case R_386_NONE: |
| return R_NONE; |
| default: |
| return R_INVALID; |
| } |
| } |
| |
| RelExpr X86::adjustRelaxExpr(RelType Type, const uint8_t *Data, |
| RelExpr Expr) const { |
| switch (Expr) { |
| default: |
| return Expr; |
| case R_RELAX_TLS_GD_TO_IE: |
| return R_RELAX_TLS_GD_TO_IE_END; |
| case R_RELAX_TLS_GD_TO_LE: |
| return R_RELAX_TLS_GD_TO_LE_NEG; |
| } |
| } |
| |
| void X86::writeGotPltHeader(uint8_t *Buf) const { |
| write32le(Buf, InX::Dynamic->getVA()); |
| } |
| |
| void X86::writeGotPlt(uint8_t *Buf, const Symbol &S) const { |
| // Entries in .got.plt initially points back to the corresponding |
| // PLT entries with a fixed offset to skip the first instruction. |
| write32le(Buf, S.getPltVA() + 6); |
| } |
| |
| void X86::writeIgotPlt(uint8_t *Buf, const Symbol &S) const { |
| // An x86 entry is the address of the ifunc resolver function. |
| write32le(Buf, S.getVA()); |
| } |
| |
| RelType X86::getDynRel(RelType Type) const { |
| if (Type == R_386_TLS_LE) |
| return R_386_TLS_TPOFF; |
| if (Type == R_386_TLS_LE_32) |
| return R_386_TLS_TPOFF32; |
| return Type; |
| } |
| |
| void X86::writePltHeader(uint8_t *Buf) const { |
| if (Config->Pic) { |
| const uint8_t V[] = { |
| 0xff, 0xb3, 0x04, 0x00, 0x00, 0x00, // pushl GOTPLT+4(%ebx) |
| 0xff, 0xa3, 0x08, 0x00, 0x00, 0x00, // jmp *GOTPLT+8(%ebx) |
| 0x90, 0x90, 0x90, 0x90 // nop |
| }; |
| memcpy(Buf, V, sizeof(V)); |
| |
| uint32_t Ebx = InX::Got->getVA() + InX::Got->getSize(); |
| uint32_t GotPlt = InX::GotPlt->getVA() - Ebx; |
| write32le(Buf + 2, GotPlt + 4); |
| write32le(Buf + 8, GotPlt + 8); |
| return; |
| } |
| |
| const uint8_t PltData[] = { |
| 0xff, 0x35, 0, 0, 0, 0, // pushl (GOTPLT+4) |
| 0xff, 0x25, 0, 0, 0, 0, // jmp *(GOTPLT+8) |
| 0x90, 0x90, 0x90, 0x90, // nop |
| }; |
| memcpy(Buf, PltData, sizeof(PltData)); |
| uint32_t GotPlt = InX::GotPlt->getVA(); |
| write32le(Buf + 2, GotPlt + 4); |
| write32le(Buf + 8, GotPlt + 8); |
| } |
| |
| void X86::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, |
| uint64_t PltEntryAddr, int32_t Index, |
| unsigned RelOff) const { |
| const uint8_t Inst[] = { |
| 0xff, 0x00, 0, 0, 0, 0, // jmp *foo_in_GOT or jmp *foo@GOT(%ebx) |
| 0x68, 0, 0, 0, 0, // pushl $reloc_offset |
| 0xe9, 0, 0, 0, 0, // jmp .PLT0@PC |
| }; |
| memcpy(Buf, Inst, sizeof(Inst)); |
| |
| if (Config->Pic) { |
| // jmp *foo@GOT(%ebx) |
| uint32_t Ebx = InX::Got->getVA() + InX::Got->getSize(); |
| Buf[1] = 0xa3; |
| write32le(Buf + 2, GotPltEntryAddr - Ebx); |
| } else { |
| // jmp *foo_in_GOT |
| Buf[1] = 0x25; |
| write32le(Buf + 2, GotPltEntryAddr); |
| } |
| |
| write32le(Buf + 7, RelOff); |
| write32le(Buf + 12, -getPltEntryOffset(Index) - 16); |
| } |
| |
| int64_t X86::getImplicitAddend(const uint8_t *Buf, RelType Type) const { |
| switch (Type) { |
| case R_386_8: |
| case R_386_PC8: |
| return SignExtend64<8>(*Buf); |
| case R_386_16: |
| case R_386_PC16: |
| return SignExtend64<16>(read16le(Buf)); |
| case R_386_32: |
| case R_386_GOT32: |
| case R_386_GOT32X: |
| case R_386_GOTOFF: |
| case R_386_GOTPC: |
| case R_386_PC32: |
| case R_386_PLT32: |
| case R_386_TLS_LDO_32: |
| case R_386_TLS_LE: |
| return SignExtend64<32>(read32le(Buf)); |
| default: |
| return 0; |
| } |
| } |
| |
| void X86::relocateOne(uint8_t *Loc, RelType Type, uint64_t Val) const { |
| switch (Type) { |
| case R_386_8: |
| // R_386_{PC,}{8,16} are not part of the i386 psABI, but they are |
| // being used for some 16-bit programs such as boot loaders, so |
| // we want to support them. |
| checkIntUInt(Loc, Val, 8, Type); |
| *Loc = Val; |
| break; |
| case R_386_PC8: |
| checkInt(Loc, Val, 8, Type); |
| *Loc = Val; |
| break; |
| case R_386_16: |
| checkIntUInt(Loc, Val, 16, Type); |
| write16le(Loc, Val); |
| break; |
| case R_386_PC16: |
| // R_386_PC16 is normally used with 16 bit code. In that situation |
| // the PC is 16 bits, just like the addend. This means that it can |
| // point from any 16 bit address to any other if the possibility |
| // of wrapping is included. |
| // The only restriction we have to check then is that the destination |
| // address fits in 16 bits. That is impossible to do here. The problem is |
| // that we are passed the final value, which already had the |
| // current location subtracted from it. |
| // We just check that Val fits in 17 bits. This misses some cases, but |
| // should have no false positives. |
| checkInt(Loc, Val, 17, Type); |
| write16le(Loc, Val); |
| break; |
| case R_386_32: |
| case R_386_GLOB_DAT: |
| case R_386_GOT32: |
| case R_386_GOT32X: |
| case R_386_GOTOFF: |
| case R_386_GOTPC: |
| case R_386_PC32: |
| case R_386_PLT32: |
| case R_386_RELATIVE: |
| case R_386_TLS_DTPMOD32: |
| case R_386_TLS_DTPOFF32: |
| case R_386_TLS_GD: |
| case R_386_TLS_GOTIE: |
| case R_386_TLS_IE: |
| case R_386_TLS_LDM: |
| case R_386_TLS_LDO_32: |
| case R_386_TLS_LE: |
| case R_386_TLS_LE_32: |
| case R_386_TLS_TPOFF: |
| case R_386_TLS_TPOFF32: |
| checkInt(Loc, Val, 32, Type); |
| write32le(Loc, Val); |
| break; |
| default: |
| error(getErrorLocation(Loc) + "unrecognized reloc " + Twine(Type)); |
| } |
| } |
| |
| void X86::relaxTlsGdToLe(uint8_t *Loc, RelType Type, uint64_t Val) const { |
| // Convert |
| // leal x@tlsgd(, %ebx, 1), |
| // call __tls_get_addr@plt |
| // to |
| // movl %gs:0,%eax |
| // subl $x@ntpoff,%eax |
| const uint8_t Inst[] = { |
| 0x65, 0xa1, 0x00, 0x00, 0x00, 0x00, // movl %gs:0, %eax |
| 0x81, 0xe8, 0, 0, 0, 0, // subl Val(%ebx), %eax |
| }; |
| memcpy(Loc - 3, Inst, sizeof(Inst)); |
| write32le(Loc + 5, Val); |
| } |
| |
| void X86::relaxTlsGdToIe(uint8_t *Loc, RelType Type, uint64_t Val) const { |
| // Convert |
| // leal x@tlsgd(, %ebx, 1), |
| // call __tls_get_addr@plt |
| // to |
| // movl %gs:0, %eax |
| // addl x@gotntpoff(%ebx), %eax |
| const uint8_t Inst[] = { |
| 0x65, 0xa1, 0x00, 0x00, 0x00, 0x00, // movl %gs:0, %eax |
| 0x03, 0x83, 0, 0, 0, 0, // addl Val(%ebx), %eax |
| }; |
| memcpy(Loc - 3, Inst, sizeof(Inst)); |
| write32le(Loc + 5, Val); |
| } |
| |
| // In some conditions, relocations can be optimized to avoid using GOT. |
| // This function does that for Initial Exec to Local Exec case. |
| void X86::relaxTlsIeToLe(uint8_t *Loc, RelType Type, uint64_t Val) const { |
| // Ulrich's document section 6.2 says that @gotntpoff can |
| // be used with MOVL or ADDL instructions. |
| // @indntpoff is similar to @gotntpoff, but for use in |
| // position dependent code. |
| uint8_t Reg = (Loc[-1] >> 3) & 7; |
| |
| if (Type == R_386_TLS_IE) { |
| if (Loc[-1] == 0xa1) { |
| // "movl foo@indntpoff,%eax" -> "movl $foo,%eax" |
| // This case is different from the generic case below because |
| // this is a 5 byte instruction while below is 6 bytes. |
| Loc[-1] = 0xb8; |
| } else if (Loc[-2] == 0x8b) { |
| // "movl foo@indntpoff,%reg" -> "movl $foo,%reg" |
| Loc[-2] = 0xc7; |
| Loc[-1] = 0xc0 | Reg; |
| } else { |
| // "addl foo@indntpoff,%reg" -> "addl $foo,%reg" |
| Loc[-2] = 0x81; |
| Loc[-1] = 0xc0 | Reg; |
| } |
| } else { |
| assert(Type == R_386_TLS_GOTIE); |
| if (Loc[-2] == 0x8b) { |
| // "movl foo@gottpoff(%rip),%reg" -> "movl $foo,%reg" |
| Loc[-2] = 0xc7; |
| Loc[-1] = 0xc0 | Reg; |
| } else { |
| // "addl foo@gotntpoff(%rip),%reg" -> "leal foo(%reg),%reg" |
| Loc[-2] = 0x8d; |
| Loc[-1] = 0x80 | (Reg << 3) | Reg; |
| } |
| } |
| write32le(Loc, Val); |
| } |
| |
| void X86::relaxTlsLdToLe(uint8_t *Loc, RelType Type, uint64_t Val) const { |
| if (Type == R_386_TLS_LDO_32) { |
| write32le(Loc, Val); |
| return; |
| } |
| |
| // Convert |
| // leal foo(%reg),%eax |
| // call ___tls_get_addr |
| // to |
| // movl %gs:0,%eax |
| // nop |
| // leal 0(%esi,1),%esi |
| const uint8_t Inst[] = { |
| 0x65, 0xa1, 0x00, 0x00, 0x00, 0x00, // movl %gs:0,%eax |
| 0x90, // nop |
| 0x8d, 0x74, 0x26, 0x00, // leal 0(%esi,1),%esi |
| }; |
| memcpy(Loc - 2, Inst, sizeof(Inst)); |
| } |
| |
| namespace { |
| class RetpolinePic : public X86 { |
| public: |
| RetpolinePic(); |
| void writeGotPlt(uint8_t *Buf, const Symbol &S) const override; |
| void writePltHeader(uint8_t *Buf) const override; |
| void writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, uint64_t PltEntryAddr, |
| int32_t Index, unsigned RelOff) const override; |
| }; |
| |
| class RetpolineNoPic : public X86 { |
| public: |
| RetpolineNoPic(); |
| void writeGotPlt(uint8_t *Buf, const Symbol &S) const override; |
| void writePltHeader(uint8_t *Buf) const override; |
| void writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, uint64_t PltEntryAddr, |
| int32_t Index, unsigned RelOff) const override; |
| }; |
| } // namespace |
| |
| RetpolinePic::RetpolinePic() { |
| PltHeaderSize = 48; |
| PltEntrySize = 32; |
| } |
| |
| void RetpolinePic::writeGotPlt(uint8_t *Buf, const Symbol &S) const { |
| write32le(Buf, S.getPltVA() + 17); |
| } |
| |
| void RetpolinePic::writePltHeader(uint8_t *Buf) const { |
| const uint8_t Insn[] = { |
| 0xff, 0xb3, 0, 0, 0, 0, // 0: pushl GOTPLT+4(%ebx) |
| 0x50, // 6: pushl %eax |
| 0x8b, 0x83, 0, 0, 0, 0, // 7: mov GOTPLT+8(%ebx), %eax |
| 0xe8, 0x0e, 0x00, 0x00, 0x00, // d: call next |
| 0xf3, 0x90, // 12: loop: pause |
| 0x0f, 0xae, 0xe8, // 14: lfence |
| 0xeb, 0xf9, // 17: jmp loop |
| 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 19: int3; .align 16 |
| 0x89, 0x0c, 0x24, // 20: next: mov %ecx, (%esp) |
| 0x8b, 0x4c, 0x24, 0x04, // 23: mov 0x4(%esp), %ecx |
| 0x89, 0x44, 0x24, 0x04, // 27: mov %eax ,0x4(%esp) |
| 0x89, 0xc8, // 2b: mov %ecx, %eax |
| 0x59, // 2d: pop %ecx |
| 0xc3, // 2e: ret |
| 0xcc, // 2f: int3; padding |
| }; |
| memcpy(Buf, Insn, sizeof(Insn)); |
| |
| uint32_t Ebx = InX::Got->getVA() + InX::Got->getSize(); |
| uint32_t GotPlt = InX::GotPlt->getVA() - Ebx; |
| write32le(Buf + 2, GotPlt + 4); |
| write32le(Buf + 9, GotPlt + 8); |
| } |
| |
| void RetpolinePic::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, |
| uint64_t PltEntryAddr, int32_t Index, |
| unsigned RelOff) const { |
| const uint8_t Insn[] = { |
| 0x50, // pushl %eax |
| 0x8b, 0x83, 0, 0, 0, 0, // mov foo@GOT(%ebx), %eax |
| 0xe8, 0, 0, 0, 0, // call plt+0x20 |
| 0xe9, 0, 0, 0, 0, // jmp plt+0x12 |
| 0x68, 0, 0, 0, 0, // pushl $reloc_offset |
| 0xe9, 0, 0, 0, 0, // jmp plt+0 |
| 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // int3; padding |
| }; |
| memcpy(Buf, Insn, sizeof(Insn)); |
| |
| uint32_t Ebx = InX::Got->getVA() + InX::Got->getSize(); |
| unsigned Off = getPltEntryOffset(Index); |
| write32le(Buf + 3, GotPltEntryAddr - Ebx); |
| write32le(Buf + 8, -Off - 12 + 32); |
| write32le(Buf + 13, -Off - 17 + 18); |
| write32le(Buf + 18, RelOff); |
| write32le(Buf + 23, -Off - 27); |
| } |
| |
| RetpolineNoPic::RetpolineNoPic() { |
| PltHeaderSize = 48; |
| PltEntrySize = 32; |
| } |
| |
| void RetpolineNoPic::writeGotPlt(uint8_t *Buf, const Symbol &S) const { |
| write32le(Buf, S.getPltVA() + 16); |
| } |
| |
| void RetpolineNoPic::writePltHeader(uint8_t *Buf) const { |
| const uint8_t Insn[] = { |
| 0xff, 0x35, 0, 0, 0, 0, // 0: pushl GOTPLT+4 |
| 0x50, // 6: pushl %eax |
| 0xa1, 0, 0, 0, 0, // 7: mov GOTPLT+8, %eax |
| 0xe8, 0x0f, 0x00, 0x00, 0x00, // c: call next |
| 0xf3, 0x90, // 11: loop: pause |
| 0x0f, 0xae, 0xe8, // 13: lfence |
| 0xeb, 0xf9, // 16: jmp loop |
| 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 18: int3 |
| 0xcc, 0xcc, 0xcc, // 1f: int3; .align 16 |
| 0x89, 0x0c, 0x24, // 20: next: mov %ecx, (%esp) |
| 0x8b, 0x4c, 0x24, 0x04, // 23: mov 0x4(%esp), %ecx |
| 0x89, 0x44, 0x24, 0x04, // 27: mov %eax ,0x4(%esp) |
| 0x89, 0xc8, // 2b: mov %ecx, %eax |
| 0x59, // 2d: pop %ecx |
| 0xc3, // 2e: ret |
| 0xcc, // 2f: int3; padding |
| }; |
| memcpy(Buf, Insn, sizeof(Insn)); |
| |
| uint32_t GotPlt = InX::GotPlt->getVA(); |
| write32le(Buf + 2, GotPlt + 4); |
| write32le(Buf + 8, GotPlt + 8); |
| } |
| |
| void RetpolineNoPic::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, |
| uint64_t PltEntryAddr, int32_t Index, |
| unsigned RelOff) const { |
| const uint8_t Insn[] = { |
| 0x50, // 0: pushl %eax |
| 0xa1, 0, 0, 0, 0, // 1: mov foo_in_GOT, %eax |
| 0xe8, 0, 0, 0, 0, // 6: call plt+0x20 |
| 0xe9, 0, 0, 0, 0, // b: jmp plt+0x11 |
| 0x68, 0, 0, 0, 0, // 10: pushl $reloc_offset |
| 0xe9, 0, 0, 0, 0, // 15: jmp plt+0 |
| 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 1a: int3; padding |
| 0xcc, // 1f: int3; padding |
| }; |
| memcpy(Buf, Insn, sizeof(Insn)); |
| |
| unsigned Off = getPltEntryOffset(Index); |
| write32le(Buf + 2, GotPltEntryAddr); |
| write32le(Buf + 7, -Off - 11 + 32); |
| write32le(Buf + 12, -Off - 16 + 17); |
| write32le(Buf + 17, RelOff); |
| write32le(Buf + 22, -Off - 26); |
| } |
| |
| TargetInfo *elf::getX86TargetInfo() { |
| if (Config->ZRetpolineplt) { |
| if (Config->Pic) { |
| static RetpolinePic T; |
| return &T; |
| } |
| static RetpolineNoPic T; |
| return &T; |
| } |
| |
| static X86 T; |
| return &T; |
| } |
