llvm-6502/lib/MC/WinCOFFStreamer.cpp
David Majnemer 31b080d57f MC: Support aligned COMMON symbols for COFF
link.exe:
Fuzz testing has shown that COMMON symbols with size > 32 will always
have an alignment of at least 32 and all symbols with size < 32 will
have an alignment of at least the largest power of 2 less than the size
of the symbol.

binutils:
The BFD linker essentially work like the link.exe behavior but with
alignment 4 instead of 32.  The BFD linker also supports an extension to
COFF which adds an -aligncomm argument to the .drectve section which
permits specifying a precise alignment for a variable but MC currently
doesn't support editing .drectve in this way.

With all of this in mind, we decide to play a little trick: we can
ensure that the alignment will be respected by bumping the size of the
global to it's alignment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218201 91177308-0d34-0410-b5e6-96231b3b80d8
2014-09-21 09:18:07 +00:00

267 lines
9.1 KiB
C++

//===-- llvm/MC/WinCOFFStreamer.cpp -----------------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains an implementation of a Windows COFF object file streamer.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/StringExtras.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSectionCOFF.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/MCWinCOFFStreamer.h"
#include "llvm/Support/COFF.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "WinCOFFStreamer"
namespace llvm {
MCWinCOFFStreamer::MCWinCOFFStreamer(MCContext &Context, MCAsmBackend &MAB,
MCCodeEmitter &CE, raw_ostream &OS)
: MCObjectStreamer(Context, MAB, OS, &CE), CurSymbol(nullptr) {}
void MCWinCOFFStreamer::EmitInstToData(const MCInst &Inst,
const MCSubtargetInfo &STI) {
MCDataFragment *DF = getOrCreateDataFragment();
SmallVector<MCFixup, 4> Fixups;
SmallString<256> Code;
raw_svector_ostream VecOS(Code);
getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups, STI);
VecOS.flush();
// Add the fixups and data.
for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
DF->getFixups().push_back(Fixups[i]);
}
DF->getContents().append(Code.begin(), Code.end());
}
void MCWinCOFFStreamer::InitSections() {
// FIXME: this is identical to the ELF one.
// This emulates the same behavior of GNU as. This makes it easier
// to compare the output as the major sections are in the same order.
SwitchSection(getContext().getObjectFileInfo()->getTextSection());
EmitCodeAlignment(4);
SwitchSection(getContext().getObjectFileInfo()->getDataSection());
EmitCodeAlignment(4);
SwitchSection(getContext().getObjectFileInfo()->getBSSSection());
EmitCodeAlignment(4);
SwitchSection(getContext().getObjectFileInfo()->getTextSection());
}
void MCWinCOFFStreamer::EmitLabel(MCSymbol *Symbol) {
assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
MCObjectStreamer::EmitLabel(Symbol);
}
void MCWinCOFFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
llvm_unreachable("not implemented");
}
void MCWinCOFFStreamer::EmitThumbFunc(MCSymbol *Func) {
llvm_unreachable("not implemented");
}
bool MCWinCOFFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
MCSymbolAttr Attribute) {
assert(Symbol && "Symbol must be non-null!");
assert((!Symbol->isInSection() ||
Symbol->getSection().getVariant() == MCSection::SV_COFF) &&
"Got non-COFF section in the COFF backend!");
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
switch (Attribute) {
default: return false;
case MCSA_WeakReference:
case MCSA_Weak:
SD.modifyFlags(COFF::SF_WeakExternal, COFF::SF_WeakExternal);
SD.setExternal(true);
break;
case MCSA_Global:
SD.setExternal(true);
break;
}
return true;
}
void MCWinCOFFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
llvm_unreachable("not implemented");
}
void MCWinCOFFStreamer::BeginCOFFSymbolDef(MCSymbol const *Symbol) {
assert((!Symbol->isInSection() ||
Symbol->getSection().getVariant() == MCSection::SV_COFF) &&
"Got non-COFF section in the COFF backend!");
if (CurSymbol)
FatalError("starting a new symbol definition without completing the "
"previous one");
CurSymbol = Symbol;
}
void MCWinCOFFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
if (!CurSymbol)
FatalError("storage class specified outside of symbol definition");
if (StorageClass & ~0xff)
FatalError(Twine("storage class value '") + itostr(StorageClass) +
"' out of range");
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*CurSymbol);
SD.modifyFlags(StorageClass << COFF::SF_ClassShift, COFF::SF_ClassMask);
}
void MCWinCOFFStreamer::EmitCOFFSymbolType(int Type) {
if (!CurSymbol)
FatalError("symbol type specified outside of a symbol definition");
if (Type & ~0xffff)
FatalError(Twine("type value '") + itostr(Type) + "' out of range");
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*CurSymbol);
SD.modifyFlags(Type << COFF::SF_TypeShift, COFF::SF_TypeMask);
}
void MCWinCOFFStreamer::EndCOFFSymbolDef() {
if (!CurSymbol)
FatalError("ending symbol definition without starting one");
CurSymbol = nullptr;
}
void MCWinCOFFStreamer::EmitCOFFSectionIndex(MCSymbol const *Symbol) {
MCDataFragment *DF = getOrCreateDataFragment();
const MCSymbolRefExpr *SRE = MCSymbolRefExpr::Create(Symbol, getContext());
MCFixup Fixup = MCFixup::Create(DF->getContents().size(), SRE, FK_SecRel_2);
DF->getFixups().push_back(Fixup);
DF->getContents().resize(DF->getContents().size() + 4, 0);
}
void MCWinCOFFStreamer::EmitCOFFSecRel32(MCSymbol const *Symbol) {
MCDataFragment *DF = getOrCreateDataFragment();
const MCSymbolRefExpr *SRE = MCSymbolRefExpr::Create(Symbol, getContext());
MCFixup Fixup = MCFixup::Create(DF->getContents().size(), SRE, FK_SecRel_4);
DF->getFixups().push_back(Fixup);
DF->getContents().resize(DF->getContents().size() + 4, 0);
}
void MCWinCOFFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
llvm_unreachable("not supported");
}
void MCWinCOFFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
assert((!Symbol->isInSection() ||
Symbol->getSection().getVariant() == MCSection::SV_COFF) &&
"Got non-COFF section in the COFF backend!");
const Triple &T = getContext().getObjectFileInfo()->getTargetTriple();
if (T.isKnownWindowsMSVCEnvironment()) {
if (ByteAlignment > 32)
report_fatal_error("alignment is limited to 32-bytes");
} else {
// The bfd linker from binutils only supports alignments less than 4 bytes
// without inserting -aligncomm arguments into the .drectve section.
// TODO: Support inserting -aligncomm into the .drectve section.
if (ByteAlignment > 4)
report_fatal_error("alignment is limited to 4-bytes");
}
// Round size up to alignment so that we will honor the alignment request.
// TODO: We don't need to do this if we are targeting the bfd linker once we
// add support for adding -aligncomm into the .drectve section.
Size = std::max(Size, static_cast<uint64_t>(ByteAlignment));
AssignSection(Symbol, nullptr);
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
SD.setExternal(true);
SD.setCommon(Size, ByteAlignment);
}
void MCWinCOFFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
assert(!Symbol->isInSection() && "Symbol must not already have a section!");
const MCSection *Section = getContext().getObjectFileInfo()->getBSSSection();
MCSectionData &SectionData = getAssembler().getOrCreateSectionData(*Section);
if (SectionData.getAlignment() < ByteAlignment)
SectionData.setAlignment(ByteAlignment);
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
SD.setExternal(false);
AssignSection(Symbol, Section);
if (ByteAlignment != 1)
new MCAlignFragment(ByteAlignment, /*_Value=*/0, /*_ValueSize=*/0,
ByteAlignment, &SectionData);
MCFillFragment *Fragment =
new MCFillFragment(/*_Value=*/0, /*_ValueSize=*/0, Size, &SectionData);
SD.setFragment(Fragment);
}
void MCWinCOFFStreamer::EmitZerofill(const MCSection *Section,
MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
llvm_unreachable("not implemented");
}
void MCWinCOFFStreamer::EmitTBSSSymbol(const MCSection *Section,
MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
llvm_unreachable("not implemented");
}
void MCWinCOFFStreamer::EmitFileDirective(StringRef Filename) {
getAssembler().addFileName(Filename);
}
// TODO: Implement this if you want to emit .comment section in COFF obj files.
void MCWinCOFFStreamer::EmitIdent(StringRef IdentString) {
llvm_unreachable("not implemented");
}
void MCWinCOFFStreamer::EmitWinEHHandlerData() {
llvm_unreachable("not implemented");
}
void MCWinCOFFStreamer::FinishImpl() {
MCObjectStreamer::FinishImpl();
}
LLVM_ATTRIBUTE_NORETURN
void MCWinCOFFStreamer::FatalError(const Twine &Msg) const {
getContext().FatalError(SMLoc(), Msg);
}
}