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actuall addresses in a .o file, so it is better to let the MachO writer compute it. This is good for two reasons. First, areas that shouldn't care about addresses now don't have access to it. Second, the layout of each section is independent. I should use this in a subsequent commit to speed it up. Most of the patch is just removing the section address computation. The two interesting parts are the change on how we handle padding in the end of sections and how MachO can get the address of a-b when a and b are in different sections. Since now the expression evaluation normally doesn't know the section address, it will think that a-b needs relocation and let the MachO writer know. Once it has computed the section addresses, it calls back the expression evaluation with the section addresses to resolve these expressions. The remaining problem is the handling of padding. Currently it will create a special alignment fragment at the end. Since that fragment doesn't update the alignment of the section, it needs the real address to be computed. Since now the layout will not compute a-b with a and b in different sections, the only effect that the special alignment fragment has is update the address size of the section. This can also be done by the MachO writer. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121076 91177308-0d34-0410-b5e6-96231b3b80d8
403 lines
15 KiB
C++
403 lines
15 KiB
C++
//===- lib/MC/MCMachOStreamer.cpp - Mach-O Object Output ------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/MC/MCStreamer.h"
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#include "llvm/MC/MCAssembler.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCCodeEmitter.h"
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#include "llvm/MC/MCExpr.h"
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#include "llvm/MC/MCInst.h"
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#include "llvm/MC/MCObjectStreamer.h"
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#include "llvm/MC/MCSection.h"
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#include "llvm/MC/MCSymbol.h"
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#include "llvm/MC/MCMachOSymbolFlags.h"
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#include "llvm/MC/MCSectionMachO.h"
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#include "llvm/MC/MCDwarf.h"
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#include "llvm/Support/Dwarf.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetAsmBackend.h"
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using namespace llvm;
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namespace {
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class MCMachOStreamer : public MCObjectStreamer {
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private:
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virtual void EmitInstToData(const MCInst &Inst);
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public:
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MCMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
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raw_ostream &OS, MCCodeEmitter *Emitter)
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: MCObjectStreamer(Context, TAB, OS, Emitter) {}
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/// @name MCStreamer Interface
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/// @{
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virtual void InitSections();
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virtual void EmitLabel(MCSymbol *Symbol);
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virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
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virtual void EmitThumbFunc(MCSymbol *Func);
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virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
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virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
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virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
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virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
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unsigned ByteAlignment);
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virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
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assert(0 && "macho doesn't support this directive");
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}
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virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
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assert(0 && "macho doesn't support this directive");
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}
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virtual void EmitCOFFSymbolType(int Type) {
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assert(0 && "macho doesn't support this directive");
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}
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virtual void EndCOFFSymbolDef() {
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assert(0 && "macho doesn't support this directive");
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}
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virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
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assert(0 && "macho doesn't support this directive");
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}
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virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
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assert(0 && "macho doesn't support this directive");
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}
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virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
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unsigned Size = 0, unsigned ByteAlignment = 0);
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virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
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uint64_t Size, unsigned ByteAlignment = 0);
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virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
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virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
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unsigned ValueSize = 1,
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unsigned MaxBytesToEmit = 0);
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virtual void EmitCodeAlignment(unsigned ByteAlignment,
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unsigned MaxBytesToEmit = 0);
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virtual void EmitFileDirective(StringRef Filename) {
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// FIXME: Just ignore the .file; it isn't important enough to fail the
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// entire assembly.
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//report_fatal_error("unsupported directive: '.file'");
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}
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virtual void Finish();
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/// @}
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};
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} // end anonymous namespace.
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void MCMachOStreamer::InitSections() {
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SwitchSection(getContext().getMachOSection("__TEXT", "__text",
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MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
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0, SectionKind::getText()));
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}
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void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
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assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
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// isSymbolLinkerVisible uses the section.
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Symbol->setSection(*CurSection);
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// We have to create a new fragment if this is an atom defining symbol,
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// fragments cannot span atoms.
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if (getAssembler().isSymbolLinkerVisible(*Symbol))
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new MCDataFragment(getCurrentSectionData());
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MCObjectStreamer::EmitLabel(Symbol);
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MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
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// This causes the reference type flag to be cleared. Darwin 'as' was "trying"
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// to clear the weak reference and weak definition bits too, but the
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// implementation was buggy. For now we just try to match 'as', for
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// diffability.
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//
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// FIXME: Cleanup this code, these bits should be emitted based on semantic
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// properties, not on the order of definition, etc.
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SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
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}
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void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
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switch (Flag) {
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case MCAF_SyntaxUnified: return; // no-op here.
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case MCAF_Code16: return; // no-op here.
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case MCAF_Code32: return; // no-op here.
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case MCAF_SubsectionsViaSymbols:
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getAssembler().setSubsectionsViaSymbols(true);
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return;
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default:
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llvm_unreachable("invalid assembler flag!");
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}
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}
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void MCMachOStreamer::EmitThumbFunc(MCSymbol *Func) {
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// FIXME: Flag the function ISA as thumb with DW_AT_APPLE_isa.
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}
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void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
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// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
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// MCObjectStreamer.
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// FIXME: Lift context changes into super class.
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getAssembler().getOrCreateSymbolData(*Symbol);
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Symbol->setVariableValue(AddValueSymbols(Value));
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}
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void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
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MCSymbolAttr Attribute) {
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// Indirect symbols are handled differently, to match how 'as' handles
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// them. This makes writing matching .o files easier.
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if (Attribute == MCSA_IndirectSymbol) {
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// Note that we intentionally cannot use the symbol data here; this is
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// important for matching the string table that 'as' generates.
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IndirectSymbolData ISD;
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ISD.Symbol = Symbol;
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ISD.SectionData = getCurrentSectionData();
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getAssembler().getIndirectSymbols().push_back(ISD);
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return;
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}
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// Adding a symbol attribute always introduces the symbol, note that an
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// important side effect of calling getOrCreateSymbolData here is to register
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// the symbol with the assembler.
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MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
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// The implementation of symbol attributes is designed to match 'as', but it
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// leaves much to desired. It doesn't really make sense to arbitrarily add and
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// remove flags, but 'as' allows this (in particular, see .desc).
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//
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// In the future it might be worth trying to make these operations more well
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// defined.
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switch (Attribute) {
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case MCSA_Invalid:
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case MCSA_ELF_TypeFunction:
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case MCSA_ELF_TypeIndFunction:
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case MCSA_ELF_TypeObject:
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case MCSA_ELF_TypeTLS:
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case MCSA_ELF_TypeCommon:
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case MCSA_ELF_TypeNoType:
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case MCSA_ELF_TypeGnuUniqueObject:
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case MCSA_IndirectSymbol:
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case MCSA_Hidden:
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case MCSA_Internal:
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case MCSA_Protected:
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case MCSA_Weak:
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case MCSA_Local:
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assert(0 && "Invalid symbol attribute for Mach-O!");
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break;
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case MCSA_Global:
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SD.setExternal(true);
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// This effectively clears the undefined lazy bit, in Darwin 'as', although
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// it isn't very consistent because it implements this as part of symbol
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// lookup.
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//
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// FIXME: Cleanup this code, these bits should be emitted based on semantic
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// properties, not on the order of definition, etc.
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SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeUndefinedLazy);
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break;
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case MCSA_LazyReference:
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// FIXME: This requires -dynamic.
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SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
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if (Symbol->isUndefined())
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SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
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break;
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// Since .reference sets the no dead strip bit, it is equivalent to
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// .no_dead_strip in practice.
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case MCSA_Reference:
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case MCSA_NoDeadStrip:
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SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
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break;
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case MCSA_SymbolResolver:
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SD.setFlags(SD.getFlags() | SF_SymbolResolver);
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break;
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case MCSA_PrivateExtern:
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SD.setExternal(true);
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SD.setPrivateExtern(true);
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break;
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case MCSA_WeakReference:
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// FIXME: This requires -dynamic.
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if (Symbol->isUndefined())
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SD.setFlags(SD.getFlags() | SF_WeakReference);
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break;
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case MCSA_WeakDefinition:
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// FIXME: 'as' enforces that this is defined and global. The manual claims
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// it has to be in a coalesced section, but this isn't enforced.
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SD.setFlags(SD.getFlags() | SF_WeakDefinition);
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break;
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case MCSA_WeakDefAutoPrivate:
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SD.setFlags(SD.getFlags() | SF_WeakDefinition | SF_WeakReference);
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break;
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}
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}
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void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
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// Encode the 'desc' value into the lowest implementation defined bits.
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assert(DescValue == (DescValue & SF_DescFlagsMask) &&
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"Invalid .desc value!");
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getAssembler().getOrCreateSymbolData(*Symbol).setFlags(
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DescValue & SF_DescFlagsMask);
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}
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void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
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unsigned ByteAlignment) {
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// FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
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assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
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MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
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SD.setExternal(true);
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SD.setCommon(Size, ByteAlignment);
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}
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void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
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unsigned Size, unsigned ByteAlignment) {
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MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
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// The symbol may not be present, which only creates the section.
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if (!Symbol)
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return;
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// FIXME: Assert that this section has the zerofill type.
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assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
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MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
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// Emit an align fragment if necessary.
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if (ByteAlignment != 1)
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new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectData);
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MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
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SD.setFragment(F);
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Symbol->setSection(*Section);
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// Update the maximum alignment on the zero fill section if necessary.
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if (ByteAlignment > SectData.getAlignment())
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SectData.setAlignment(ByteAlignment);
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}
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// This should always be called with the thread local bss section. Like the
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// .zerofill directive this doesn't actually switch sections on us.
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void MCMachOStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
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uint64_t Size, unsigned ByteAlignment) {
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EmitZerofill(Section, Symbol, Size, ByteAlignment);
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return;
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}
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void MCMachOStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
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// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
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// MCObjectStreamer.
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getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
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}
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void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
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int64_t Value, unsigned ValueSize,
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unsigned MaxBytesToEmit) {
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// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
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// MCObjectStreamer.
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if (MaxBytesToEmit == 0)
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MaxBytesToEmit = ByteAlignment;
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new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
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getCurrentSectionData());
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// Update the maximum alignment on the current section if necessary.
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if (ByteAlignment > getCurrentSectionData()->getAlignment())
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getCurrentSectionData()->setAlignment(ByteAlignment);
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}
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void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
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unsigned MaxBytesToEmit) {
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// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
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// MCObjectStreamer.
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if (MaxBytesToEmit == 0)
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MaxBytesToEmit = ByteAlignment;
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MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
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getCurrentSectionData());
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F->setEmitNops(true);
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// Update the maximum alignment on the current section if necessary.
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if (ByteAlignment > getCurrentSectionData()->getAlignment())
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getCurrentSectionData()->setAlignment(ByteAlignment);
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}
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void MCMachOStreamer::EmitInstToData(const MCInst &Inst) {
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MCDataFragment *DF = getOrCreateDataFragment();
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SmallVector<MCFixup, 4> Fixups;
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SmallString<256> Code;
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raw_svector_ostream VecOS(Code);
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getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
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VecOS.flush();
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// Add the fixups and data.
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for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
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Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
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DF->addFixup(Fixups[i]);
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}
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DF->getContents().append(Code.begin(), Code.end());
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}
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void MCMachOStreamer::Finish() {
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// Dump out the dwarf file & directory tables and line tables.
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if (getContext().hasDwarfFiles()) {
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const MCSection *DwarfLineSection = getContext().getMachOSection("__DWARF",
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"__debug_line",
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MCSectionMachO::S_ATTR_DEBUG,
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0, SectionKind::getDataRelLocal());
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MCDwarfFileTable::Emit(this, DwarfLineSection);
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}
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// We have to set the fragment atom associations so we can relax properly for
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// Mach-O.
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// First, scan the symbol table to build a lookup table from fragments to
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// defining symbols.
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DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
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for (MCAssembler::symbol_iterator it = getAssembler().symbol_begin(),
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ie = getAssembler().symbol_end(); it != ie; ++it) {
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if (getAssembler().isSymbolLinkerVisible(it->getSymbol()) &&
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it->getFragment()) {
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// An atom defining symbol should never be internal to a fragment.
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assert(it->getOffset() == 0 && "Invalid offset in atom defining symbol!");
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DefiningSymbolMap[it->getFragment()] = it;
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}
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}
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// Set the fragment atom associations by tracking the last seen atom defining
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// symbol.
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for (MCAssembler::iterator it = getAssembler().begin(),
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ie = getAssembler().end(); it != ie; ++it) {
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MCSymbolData *CurrentAtom = 0;
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for (MCSectionData::iterator it2 = it->begin(),
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ie2 = it->end(); it2 != ie2; ++it2) {
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if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
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CurrentAtom = SD;
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it2->setAtom(CurrentAtom);
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}
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}
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this->MCObjectStreamer::Finish();
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}
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MCStreamer *llvm::createMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
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raw_ostream &OS, MCCodeEmitter *CE,
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bool RelaxAll) {
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MCMachOStreamer *S = new MCMachOStreamer(Context, TAB, OS, CE);
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if (RelaxAll)
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S->getAssembler().setRelaxAll(true);
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return S;
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}
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