//===-- AArch64MachObjectWriter.cpp - ARM Mach Object Writer --------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// #include "MCTargetDesc/AArch64FixupKinds.h" #include "MCTargetDesc/AArch64MCTargetDesc.h" #include "llvm/ADT/Twine.h" #include "llvm/MC/MCAsmInfo.h" #include "llvm/MC/MCAsmLayout.h" #include "llvm/MC/MCAssembler.h" #include "llvm/MC/MCContext.h" #include "llvm/MC/MCExpr.h" #include "llvm/MC/MCFixup.h" #include "llvm/MC/MCMachObjectWriter.h" #include "llvm/MC/MCSectionMachO.h" #include "llvm/MC/MCValue.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/MachO.h" using namespace llvm; namespace { class AArch64MachObjectWriter : public MCMachObjectTargetWriter { bool getAArch64FixupKindMachOInfo(const MCFixup &Fixup, unsigned &RelocType, const MCSymbolRefExpr *Sym, unsigned &Log2Size, const MCAssembler &Asm); public: AArch64MachObjectWriter(uint32_t CPUType, uint32_t CPUSubtype) : MCMachObjectTargetWriter(true /* is64Bit */, CPUType, CPUSubtype, /*UseAggressiveSymbolFolding=*/true) {} void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, uint64_t &FixedValue) override; }; } bool AArch64MachObjectWriter::getAArch64FixupKindMachOInfo( const MCFixup &Fixup, unsigned &RelocType, const MCSymbolRefExpr *Sym, unsigned &Log2Size, const MCAssembler &Asm) { RelocType = unsigned(MachO::ARM64_RELOC_UNSIGNED); Log2Size = ~0U; switch ((unsigned)Fixup.getKind()) { default: return false; case FK_Data_1: Log2Size = llvm::Log2_32(1); return true; case FK_Data_2: Log2Size = llvm::Log2_32(2); return true; case FK_Data_4: Log2Size = llvm::Log2_32(4); if (Sym->getKind() == MCSymbolRefExpr::VK_GOT) RelocType = unsigned(MachO::ARM64_RELOC_POINTER_TO_GOT); return true; case FK_Data_8: Log2Size = llvm::Log2_32(8); if (Sym->getKind() == MCSymbolRefExpr::VK_GOT) RelocType = unsigned(MachO::ARM64_RELOC_POINTER_TO_GOT); return true; case AArch64::fixup_aarch64_add_imm12: case AArch64::fixup_aarch64_ldst_imm12_scale1: case AArch64::fixup_aarch64_ldst_imm12_scale2: case AArch64::fixup_aarch64_ldst_imm12_scale4: case AArch64::fixup_aarch64_ldst_imm12_scale8: case AArch64::fixup_aarch64_ldst_imm12_scale16: Log2Size = llvm::Log2_32(4); switch (Sym->getKind()) { default: llvm_unreachable("Unexpected symbol reference variant kind!"); case MCSymbolRefExpr::VK_PAGEOFF: RelocType = unsigned(MachO::ARM64_RELOC_PAGEOFF12); return true; case MCSymbolRefExpr::VK_GOTPAGEOFF: RelocType = unsigned(MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12); return true; case MCSymbolRefExpr::VK_TLVPPAGEOFF: RelocType = unsigned(MachO::ARM64_RELOC_TLVP_LOAD_PAGEOFF12); return true; } case AArch64::fixup_aarch64_pcrel_adrp_imm21: Log2Size = llvm::Log2_32(4); // This encompasses the relocation for the whole 21-bit value. switch (Sym->getKind()) { default: Asm.getContext().FatalError(Fixup.getLoc(), "ADR/ADRP relocations must be GOT relative"); case MCSymbolRefExpr::VK_PAGE: RelocType = unsigned(MachO::ARM64_RELOC_PAGE21); return true; case MCSymbolRefExpr::VK_GOTPAGE: RelocType = unsigned(MachO::ARM64_RELOC_GOT_LOAD_PAGE21); return true; case MCSymbolRefExpr::VK_TLVPPAGE: RelocType = unsigned(MachO::ARM64_RELOC_TLVP_LOAD_PAGE21); return true; } return true; case AArch64::fixup_aarch64_pcrel_branch26: case AArch64::fixup_aarch64_pcrel_call26: Log2Size = llvm::Log2_32(4); RelocType = unsigned(MachO::ARM64_RELOC_BRANCH26); return true; } } static bool canUseLocalRelocation(const MCSectionMachO &Section, const MCSymbol &Symbol, unsigned Log2Size) { // Debug info sections can use local relocations. if (Section.hasAttribute(MachO::S_ATTR_DEBUG)) return true; // Otherwise, only pointer sized relocations are supported. if (Log2Size != 3) return false; // But only if they don't point to a few forbidden sections. if (!Symbol.isInSection()) return true; const MCSectionMachO &RefSec = cast(Symbol.getSection()); if (RefSec.getType() == MachO::S_CSTRING_LITERALS) return false; if (RefSec.getSegmentName() == "__DATA" && RefSec.getSectionName() == "__cfstring") return false; if (RefSec.getSegmentName() == "__DATA" && RefSec.getSectionName() == "__objc_classrefs") return false; return true; } void AArch64MachObjectWriter::RecordRelocation( MachObjectWriter *Writer, MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, uint64_t &FixedValue) { unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind()); // See . uint32_t FixupOffset = Layout.getFragmentOffset(Fragment); unsigned Log2Size = 0; int64_t Value = 0; unsigned Index = 0; unsigned Type = 0; unsigned Kind = Fixup.getKind(); const MCSymbolData *RelSymbol = nullptr; FixupOffset += Fixup.getOffset(); // AArch64 pcrel relocation addends do not include the section offset. if (IsPCRel) FixedValue += FixupOffset; // ADRP fixups use relocations for the whole symbol value and only // put the addend in the instruction itself. Clear out any value the // generic code figured out from the sybmol definition. if (Kind == AArch64::fixup_aarch64_pcrel_adrp_imm21) FixedValue = 0; // imm19 relocations are for conditional branches, which require // assembler local symbols. If we got here, that's not what we have, // so complain loudly. if (Kind == AArch64::fixup_aarch64_pcrel_branch19) { Asm.getContext().FatalError(Fixup.getLoc(), "conditional branch requires assembler-local" " label. '" + Target.getSymA()->getSymbol().getName() + "' is external."); return; } // 14-bit branch relocations should only target internal labels, and so // should never get here. if (Kind == AArch64::fixup_aarch64_pcrel_branch14) { Asm.getContext().FatalError(Fixup.getLoc(), "Invalid relocation on conditional branch!"); return; } if (!getAArch64FixupKindMachOInfo(Fixup, Type, Target.getSymA(), Log2Size, Asm)) { Asm.getContext().FatalError(Fixup.getLoc(), "unknown AArch64 fixup kind!"); return; } Value = Target.getConstant(); if (Target.isAbsolute()) { // constant // FIXME: Should this always be extern? // SymbolNum of 0 indicates the absolute section. Type = MachO::ARM64_RELOC_UNSIGNED; if (IsPCRel) { Asm.getContext().FatalError(Fixup.getLoc(), "PC relative absolute relocation!"); // FIXME: x86_64 sets the type to a branch reloc here. Should we do // something similar? } } else if (Target.getSymB()) { // A - B + constant const MCSymbol *A = &Target.getSymA()->getSymbol(); const MCSymbolData &A_SD = Asm.getSymbolData(*A); const MCSymbolData *A_Base = Asm.getAtom(&A_SD); const MCSymbol *B = &Target.getSymB()->getSymbol(); const MCSymbolData &B_SD = Asm.getSymbolData(*B); const MCSymbolData *B_Base = Asm.getAtom(&B_SD); // Check for "_foo@got - .", which comes through here as: // Ltmp0: // ... _foo@got - Ltmp0 if (Target.getSymA()->getKind() == MCSymbolRefExpr::VK_GOT && Target.getSymB()->getKind() == MCSymbolRefExpr::VK_None && Layout.getSymbolOffset(&B_SD) == Layout.getFragmentOffset(Fragment) + Fixup.getOffset()) { // SymB is the PC, so use a PC-rel pointer-to-GOT relocation. Type = MachO::ARM64_RELOC_POINTER_TO_GOT; IsPCRel = 1; MachO::any_relocation_info MRE; MRE.r_word0 = FixupOffset; MRE.r_word1 = (IsPCRel << 24) | (Log2Size << 25) | (Type << 28); Writer->addRelocation(A_Base, Fragment->getParent(), MRE); return; } else if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None || Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None) // Otherwise, neither symbol can be modified. Asm.getContext().FatalError(Fixup.getLoc(), "unsupported relocation of modified symbol"); // We don't support PCrel relocations of differences. if (IsPCRel) Asm.getContext().FatalError(Fixup.getLoc(), "unsupported pc-relative relocation of " "difference"); // AArch64 always uses external relocations. If there is no symbol to use as // a base address (a local symbol with no preceding non-local symbol), // error out. // // FIXME: We should probably just synthesize an external symbol and use // that. if (!A_Base) Asm.getContext().FatalError( Fixup.getLoc(), "unsupported relocation of local symbol '" + A->getName() + "'. Must have non-local symbol earlier in section."); if (!B_Base) Asm.getContext().FatalError( Fixup.getLoc(), "unsupported relocation of local symbol '" + B->getName() + "'. Must have non-local symbol earlier in section."); if (A_Base == B_Base && A_Base) Asm.getContext().FatalError(Fixup.getLoc(), "unsupported relocation with identical base"); Value += (!A_SD.getFragment() ? 0 : Writer->getSymbolAddress(&A_SD, Layout)) - (!A_Base || !A_Base->getFragment() ? 0 : Writer->getSymbolAddress(A_Base, Layout)); Value -= (!B_SD.getFragment() ? 0 : Writer->getSymbolAddress(&B_SD, Layout)) - (!B_Base || !B_Base->getFragment() ? 0 : Writer->getSymbolAddress(B_Base, Layout)); Type = MachO::ARM64_RELOC_UNSIGNED; MachO::any_relocation_info MRE; MRE.r_word0 = FixupOffset; MRE.r_word1 = (IsPCRel << 24) | (Log2Size << 25) | (Type << 28); Writer->addRelocation(A_Base, Fragment->getParent(), MRE); RelSymbol = B_Base; Type = MachO::ARM64_RELOC_SUBTRACTOR; } else { // A + constant const MCSymbol *Symbol = &Target.getSymA()->getSymbol(); const MCSectionMachO &Section = static_cast( Fragment->getParent()->getSection()); bool CanUseLocalRelocation = canUseLocalRelocation(Section, *Symbol, Log2Size); if (Symbol->isTemporary() && (Value || !CanUseLocalRelocation)) { const MCSection &Sec = Symbol->getSection(); if (!Asm.getContext().getAsmInfo()->isSectionAtomizableBySymbols(Sec)) Asm.addLocalUsedInReloc(*Symbol); } const MCSymbolData &SD = Asm.getSymbolData(*Symbol); const MCSymbolData *Base = Asm.getAtom(&SD); // If the symbol is a variable and we weren't able to get a Base for it // (i.e., it's not in the symbol table associated with a section) resolve // the relocation based its expansion instead. if (Symbol->isVariable() && !Base) { // If the evaluation is an absolute value, just use that directly // to keep things easy. int64_t Res; if (SD.getSymbol().getVariableValue()->EvaluateAsAbsolute( Res, Layout, Writer->getSectionAddressMap())) { FixedValue = Res; return; } // FIXME: Will the Target we already have ever have any data in it // we need to preserve and merge with the new Target? How about // the FixedValue? if (!Symbol->getVariableValue()->EvaluateAsRelocatable(Target, &Layout, &Fixup)) Asm.getContext().FatalError(Fixup.getLoc(), "unable to resolve variable '" + Symbol->getName() + "'"); return RecordRelocation(Writer, Asm, Layout, Fragment, Fixup, Target, FixedValue); } // Relocations inside debug sections always use local relocations when // possible. This seems to be done because the debugger doesn't fully // understand relocation entries and expects to find values that // have already been fixed up. if (Symbol->isInSection()) { if (Section.hasAttribute(MachO::S_ATTR_DEBUG)) Base = nullptr; } // AArch64 uses external relocations as much as possible. For debug // sections, and for pointer-sized relocations (.quad), we allow section // relocations. It's code sections that run into trouble. if (Base) { RelSymbol = Base; // Add the local offset, if needed. if (Base != &SD) Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base); } else if (Symbol->isInSection()) { if (!CanUseLocalRelocation) Asm.getContext().FatalError( Fixup.getLoc(), "unsupported relocation of local symbol '" + Symbol->getName() + "'. Must have non-local symbol earlier in section."); // Adjust the relocation to be section-relative. // The index is the section ordinal (1-based). const MCSectionData &SymSD = Asm.getSectionData(SD.getSymbol().getSection()); Index = SymSD.getOrdinal() + 1; Value += Writer->getSymbolAddress(&SD, Layout); if (IsPCRel) Value -= Writer->getFragmentAddress(Fragment, Layout) + Fixup.getOffset() + (1ULL << Log2Size); } else { // Resolve constant variables. if (SD.getSymbol().isVariable()) { int64_t Res; if (SD.getSymbol().getVariableValue()->EvaluateAsAbsolute( Res, Layout, Writer->getSectionAddressMap())) { FixedValue = Res; return; } } Asm.getContext().FatalError(Fixup.getLoc(), "unsupported relocation of variable '" + Symbol->getName() + "'"); } } // If the relocation kind is Branch26, Page21, or Pageoff12, any addend // is represented via an Addend relocation, not encoded directly into // the instruction. if ((Type == MachO::ARM64_RELOC_BRANCH26 || Type == MachO::ARM64_RELOC_PAGE21 || Type == MachO::ARM64_RELOC_PAGEOFF12) && Value) { assert((Value & 0xff000000) == 0 && "Added relocation out of range!"); MachO::any_relocation_info MRE; MRE.r_word0 = FixupOffset; MRE.r_word1 = (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28); Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE); // Now set up the Addend relocation. Type = MachO::ARM64_RELOC_ADDEND; Index = Value; RelSymbol = nullptr; IsPCRel = 0; Log2Size = 2; // Put zero into the instruction itself. The addend is in the relocation. Value = 0; } // If there's any addend left to handle, encode it in the instruction. FixedValue = Value; // struct relocation_info (8 bytes) MachO::any_relocation_info MRE; MRE.r_word0 = FixupOffset; MRE.r_word1 = (Index << 0) | (IsPCRel << 24) | (Log2Size << 25) | (Type << 28); Writer->addRelocation(RelSymbol, Fragment->getParent(), MRE); } MCObjectWriter *llvm::createAArch64MachObjectWriter(raw_pwrite_stream &OS, uint32_t CPUType, uint32_t CPUSubtype) { return createMachObjectWriter( new AArch64MachObjectWriter(CPUType, CPUSubtype), OS, /*IsLittleEndian=*/true); }