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llvm-project/llvm/lib/MC/MCAssembler.cpp

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//===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "assembler"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetRegistry.h"
#include "llvm/Target/TargetAsmBackend.h"
#include <vector>
using namespace llvm;
namespace {
namespace stats {
STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
STATISTIC(EvaluateFixup, "Number of evaluated fixups");
STATISTIC(FragmentLayouts, "Number of fragment layouts");
STATISTIC(ObjectBytes, "Number of emitted object file bytes");
STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
STATISTIC(SectionLayouts, "Number of section layouts");
}
}
// FIXME FIXME FIXME: There are number of places in this file where we convert
// what is a 64-bit assembler value used for computation into a value in the
// object file, which may truncate it. We should detect that truncation where
// invalid and report errors back.
/* *** */
MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
: Assembler(Asm), LastValidFragment(0)
{
// Compute the section layout order. Virtual sections must go last.
for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
if (!Asm.getBackend().isVirtualSection(it->getSection()))
SectionOrder.push_back(&*it);
for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
if (Asm.getBackend().isVirtualSection(it->getSection()))
SectionOrder.push_back(&*it);
}
bool MCAsmLayout::isSectionUpToDate(const MCSectionData *SD) const {
// The first section is always up-to-date.
unsigned Index = SD->getLayoutOrder();
if (!Index)
return true;
// Otherwise, sections are always implicitly computed when the preceeding
// fragment is layed out.
const MCSectionData *Prev = getSectionOrder()[Index - 1];
return isFragmentUpToDate(&(Prev->getFragmentList().back()));
}
bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
return (LastValidFragment &&
F->getLayoutOrder() <= LastValidFragment->getLayoutOrder());
}
void MCAsmLayout::UpdateForSlide(MCFragment *F, int SlideAmount) {
// If this fragment wasn't already up-to-date, we don't need to do anything.
if (!isFragmentUpToDate(F))
return;
// Otherwise, reset the last valid fragment to the predecessor of the
// invalidated fragment.
LastValidFragment = F->getPrevNode();
if (!LastValidFragment) {
unsigned Index = F->getParent()->getLayoutOrder();
if (Index != 0) {
MCSectionData *Prev = getSectionOrder()[Index - 1];
LastValidFragment = &(Prev->getFragmentList().back());
}
}
}
void MCAsmLayout::EnsureValid(const MCFragment *F) const {
// Advance the layout position until the fragment is up-to-date.
while (!isFragmentUpToDate(F)) {
// Advance to the next fragment.
MCFragment *Cur = LastValidFragment;
if (Cur)
Cur = Cur->getNextNode();
if (!Cur) {
unsigned NextIndex = 0;
if (LastValidFragment)
NextIndex = LastValidFragment->getParent()->getLayoutOrder() + 1;
Cur = SectionOrder[NextIndex]->begin();
}
const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
}
}
void MCAsmLayout::FragmentReplaced(MCFragment *Src, MCFragment *Dst) {
if (LastValidFragment == Src)
LastValidFragment = Dst;
Dst->Offset = Src->Offset;
Dst->EffectiveSize = Src->EffectiveSize;
}
uint64_t MCAsmLayout::getFragmentAddress(const MCFragment *F) const {
assert(F->getParent() && "Missing section()!");
return getSectionAddress(F->getParent()) + getFragmentOffset(F);
}
uint64_t MCAsmLayout::getFragmentEffectiveSize(const MCFragment *F) const {
EnsureValid(F);
assert(F->EffectiveSize != ~UINT64_C(0) && "Address not set!");
return F->EffectiveSize;
}
uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
EnsureValid(F);
assert(F->Offset != ~UINT64_C(0) && "Address not set!");
return F->Offset;
}
uint64_t MCAsmLayout::getSymbolAddress(const MCSymbolData *SD) const {
assert(SD->getFragment() && "Invalid getAddress() on undefined symbol!");
return getFragmentAddress(SD->getFragment()) + SD->getOffset();
}
uint64_t MCAsmLayout::getSectionAddress(const MCSectionData *SD) const {
EnsureValid(SD->begin());
assert(SD->Address != ~UINT64_C(0) && "Address not set!");
return SD->Address;
}
uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
// The size is the last fragment's end offset.
const MCFragment &F = SD->getFragmentList().back();
return getFragmentOffset(&F) + getFragmentEffectiveSize(&F);
}
uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
// Virtual sections have no file size.
if (getAssembler().getBackend().isVirtualSection(SD->getSection()))
return 0;
// Otherwise, the file size is the same as the address space size.
return getSectionAddressSize(SD);
}
uint64_t MCAsmLayout::getSectionSize(const MCSectionData *SD) const {
// The logical size is the address space size minus any tail padding.
uint64_t Size = getSectionAddressSize(SD);
const MCAlignFragment *AF =
dyn_cast<MCAlignFragment>(&(SD->getFragmentList().back()));
if (AF && AF->hasOnlyAlignAddress())
Size -= getFragmentEffectiveSize(AF);
return Size;
}
/* *** */
MCFragment::MCFragment() : Kind(FragmentType(~0)) {
}
MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
: Kind(_Kind), Parent(_Parent), Atom(0), EffectiveSize(~UINT64_C(0))
{
if (Parent)
Parent->getFragmentList().push_back(this);
}
/* *** */
MCSectionData::MCSectionData() : Section(0) {}
MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
: Section(&_Section),
Alignment(1),
Address(~UINT64_C(0)),
HasInstructions(false)
{
if (A)
A->getSectionList().push_back(this);
}
/* *** */
MCSymbolData::MCSymbolData() : Symbol(0) {}
MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
uint64_t _Offset, MCAssembler *A)
: Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
IsExternal(false), IsPrivateExtern(false),
CommonSize(0), CommonAlign(0), Flags(0), Index(0)
{
if (A)
A->getSymbolList().push_back(this);
}
/* *** */
MCAssembler::MCAssembler(MCContext &_Context, TargetAsmBackend &_Backend,
MCCodeEmitter &_Emitter, raw_ostream &_OS)
: Context(_Context), Backend(_Backend), Emitter(_Emitter),
OS(_OS), RelaxAll(false), SubsectionsViaSymbols(false)
{
}
MCAssembler::~MCAssembler() {
}
static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
const MCFixup &Fixup,
const MCValue Target,
const MCSection *BaseSection) {
// The effective fixup address is
// addr(atom(A)) + offset(A)
// - addr(atom(B)) - offset(B)
// - addr(<base symbol>) + <fixup offset from base symbol>
// and the offsets are not relocatable, so the fixup is fully resolved when
// addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0.
//
// The simple (Darwin, except on x86_64) way of dealing with this was to
// assume that any reference to a temporary symbol *must* be a temporary
// symbol in the same atom, unless the sections differ. Therefore, any PCrel
// relocation to a temporary symbol (in the same section) is fully
// resolved. This also works in conjunction with absolutized .set, which
// requires the compiler to use .set to absolutize the differences between
// symbols which the compiler knows to be assembly time constants, so we don't
// need to worry about considering symbol differences fully resolved.
// Non-relative fixups are only resolved if constant.
if (!BaseSection)
return Target.isAbsolute();
// Otherwise, relative fixups are only resolved if not a difference and the
// target is a temporary in the same section.
if (Target.isAbsolute() || Target.getSymB())
return false;
const MCSymbol *A = &Target.getSymA()->getSymbol();
if (!A->isTemporary() || !A->isInSection() ||
&A->getSection() != BaseSection)
return false;
return true;
}
static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFixup &Fixup,
const MCValue Target,
const MCSymbolData *BaseSymbol) {
// The effective fixup address is
// addr(atom(A)) + offset(A)
// - addr(atom(B)) - offset(B)
// - addr(BaseSymbol) + <fixup offset from base symbol>
// and the offsets are not relocatable, so the fixup is fully resolved when
// addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
//
// Note that "false" is almost always conservatively correct (it means we emit
// a relocation which is unnecessary), except when it would force us to emit a
// relocation which the target cannot encode.
const MCSymbolData *A_Base = 0, *B_Base = 0;
if (const MCSymbolRefExpr *A = Target.getSymA()) {
// Modified symbol references cannot be resolved.
if (A->getKind() != MCSymbolRefExpr::VK_None)
return false;
A_Base = Asm.getAtom(Layout, &Asm.getSymbolData(A->getSymbol()));
if (!A_Base)
return false;
}
if (const MCSymbolRefExpr *B = Target.getSymB()) {
// Modified symbol references cannot be resolved.
if (B->getKind() != MCSymbolRefExpr::VK_None)
return false;
B_Base = Asm.getAtom(Layout, &Asm.getSymbolData(B->getSymbol()));
if (!B_Base)
return false;
}
// If there is no base, A and B have to be the same atom for this fixup to be
// fully resolved.
if (!BaseSymbol)
return A_Base == B_Base;
// Otherwise, B must be missing and A must be the base.
return !B_Base && BaseSymbol == A_Base;
}
bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
// Non-temporary labels should always be visible to the linker.
if (!Symbol.isTemporary())
return true;
// Absolute temporary labels are never visible.
if (!Symbol.isInSection())
return false;
// Otherwise, check if the section requires symbols even for temporary labels.
return getBackend().doesSectionRequireSymbols(Symbol.getSection());
}
const MCSymbolData *MCAssembler::getAtom(const MCAsmLayout &Layout,
const MCSymbolData *SD) const {
// Linker visible symbols define atoms.
if (isSymbolLinkerVisible(SD->getSymbol()))
return SD;
// Absolute and undefined symbols have no defining atom.
if (!SD->getFragment())
return 0;
// Non-linker visible symbols in sections which can't be atomized have no
// defining atom.
if (!getBackend().isSectionAtomizable(
SD->getFragment()->getParent()->getSection()))
return 0;
// Otherwise, return the atom for the containing fragment.
return SD->getFragment()->getAtom();
}
bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout,
const MCFixup &Fixup, const MCFragment *DF,
MCValue &Target, uint64_t &Value) const {
++stats::EvaluateFixup;
if (!Fixup.getValue()->EvaluateAsRelocatable(Target, &Layout))
report_fatal_error("expected relocatable expression");
// FIXME: How do non-scattered symbols work in ELF? I presume the linker
// doesn't support small relocations, but then under what criteria does the
// assembler allow symbol differences?
Value = Target.getConstant();
bool IsPCRel = Emitter.getFixupKindInfo(
Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
bool IsResolved = true;
if (const MCSymbolRefExpr *A = Target.getSymA()) {
if (A->getSymbol().isDefined())
Value += Layout.getSymbolAddress(&getSymbolData(A->getSymbol()));
else
IsResolved = false;
}
if (const MCSymbolRefExpr *B = Target.getSymB()) {
if (B->getSymbol().isDefined())
Value -= Layout.getSymbolAddress(&getSymbolData(B->getSymbol()));
else
IsResolved = false;
}
// If we are using scattered symbols, determine whether this value is actually
// resolved; scattering may cause atoms to move.
if (IsResolved && getBackend().hasScatteredSymbols()) {
if (getBackend().hasReliableSymbolDifference()) {
// If this is a PCrel relocation, find the base atom (identified by its
// symbol) that the fixup value is relative to.
const MCSymbolData *BaseSymbol = 0;
if (IsPCRel) {
BaseSymbol = DF->getAtom();
if (!BaseSymbol)
IsResolved = false;
}
if (IsResolved)
IsResolved = isScatteredFixupFullyResolved(*this, Layout, Fixup, Target,
BaseSymbol);
} else {
const MCSection *BaseSection = 0;
if (IsPCRel)
BaseSection = &DF->getParent()->getSection();
IsResolved = isScatteredFixupFullyResolvedSimple(*this, Fixup, Target,
BaseSection);
}
}
if (IsPCRel)
Value -= Layout.getFragmentAddress(DF) + Fixup.getOffset();
return IsResolved;
}
uint64_t MCAssembler::ComputeFragmentSize(MCAsmLayout &Layout,
const MCFragment &F,
uint64_t SectionAddress,
uint64_t FragmentOffset) const {
switch (F.getKind()) {
case MCFragment::FT_Data:
return cast<MCDataFragment>(F).getContents().size();
case MCFragment::FT_Fill:
return cast<MCFillFragment>(F).getSize();
case MCFragment::FT_Inst:
return cast<MCInstFragment>(F).getInstSize();
case MCFragment::FT_Align: {
const MCAlignFragment &AF = cast<MCAlignFragment>(F);
assert((!AF.hasOnlyAlignAddress() || !AF.getNextNode()) &&
"Invalid OnlyAlignAddress bit, not the last fragment!");
uint64_t Size = OffsetToAlignment(SectionAddress + FragmentOffset,
AF.getAlignment());
// Honor MaxBytesToEmit.
if (Size > AF.getMaxBytesToEmit())
return 0;
return Size;
}
case MCFragment::FT_Org: {
const MCOrgFragment &OF = cast<MCOrgFragment>(F);
// FIXME: We should compute this sooner, we don't want to recurse here, and
// we would like to be more functional.
int64_t TargetLocation;
if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, &Layout))
report_fatal_error("expected assembly-time absolute expression");
// FIXME: We need a way to communicate this error.
int64_t Offset = TargetLocation - FragmentOffset;
if (Offset < 0)
report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
"' (at offset '" + Twine(FragmentOffset) + "'");
return Offset;
}
}
assert(0 && "invalid fragment kind");
return 0;
}
void MCAsmLayout::LayoutFile() {
// Initialize the first section and set the valid fragment layout point. All
// actual layout computations are done lazily.
LastValidFragment = 0;
if (!getSectionOrder().empty())
getSectionOrder().front()->Address = 0;
}
void MCAsmLayout::LayoutFragment(MCFragment *F) {
MCFragment *Prev = F->getPrevNode();
// We should never try to recompute something which is up-to-date.
assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
// We should never try to compute the fragment layout if the section isn't
// up-to-date.
assert(isSectionUpToDate(F->getParent()) &&
"Attempt to compute fragment before it's section!");
// We should never try to compute the fragment layout if it's predecessor
// isn't up-to-date.
assert((!Prev || isFragmentUpToDate(Prev)) &&
"Attempt to compute fragment before it's predecessor!");
++stats::FragmentLayouts;
// Compute the fragment start address.
uint64_t StartAddress = F->getParent()->Address;
uint64_t Address = StartAddress;
if (Prev)
Address += Prev->Offset + Prev->EffectiveSize;
// Compute fragment offset and size.
F->Offset = Address - StartAddress;
F->EffectiveSize = getAssembler().ComputeFragmentSize(*this, *F, StartAddress,
F->Offset);
LastValidFragment = F;
// If this is the last fragment in a section, update the next section address.
if (!F->getNextNode()) {
unsigned NextIndex = F->getParent()->getLayoutOrder() + 1;
if (NextIndex != getSectionOrder().size())
LayoutSection(getSectionOrder()[NextIndex]);
}
}
void MCAsmLayout::LayoutSection(MCSectionData *SD) {
unsigned SectionOrderIndex = SD->getLayoutOrder();
++stats::SectionLayouts;
// Compute the section start address.
uint64_t StartAddress = 0;
if (SectionOrderIndex) {
MCSectionData *Prev = getSectionOrder()[SectionOrderIndex - 1];
StartAddress = getSectionAddress(Prev) + getSectionAddressSize(Prev);
}
// Honor the section alignment requirements.
StartAddress = RoundUpToAlignment(StartAddress, SD->getAlignment());
// Set the section address.
SD->Address = StartAddress;
}
/// WriteFragmentData - Write the \arg F data to the output file.
static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment &F, MCObjectWriter *OW) {
uint64_t Start = OW->getStream().tell();
(void) Start;
++stats::EmittedFragments;
// FIXME: Embed in fragments instead?
uint64_t FragmentSize = Layout.getFragmentEffectiveSize(&F);
switch (F.getKind()) {
case MCFragment::FT_Align: {
MCAlignFragment &AF = cast<MCAlignFragment>(F);
uint64_t Count = FragmentSize / AF.getValueSize();
assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
// FIXME: This error shouldn't actually occur (the front end should emit
// multiple .align directives to enforce the semantics it wants), but is
// severe enough that we want to report it. How to handle this?
if (Count * AF.getValueSize() != FragmentSize)
report_fatal_error("undefined .align directive, value size '" +
Twine(AF.getValueSize()) +
"' is not a divisor of padding size '" +
Twine(FragmentSize) + "'");
// See if we are aligning with nops, and if so do that first to try to fill
// the Count bytes. Then if that did not fill any bytes or there are any
// bytes left to fill use the the Value and ValueSize to fill the rest.
// If we are aligning with nops, ask that target to emit the right data.
if (AF.hasEmitNops()) {
if (!Asm.getBackend().WriteNopData(Count, OW))
report_fatal_error("unable to write nop sequence of " +
Twine(Count) + " bytes");
break;
}
// Otherwise, write out in multiples of the value size.
for (uint64_t i = 0; i != Count; ++i) {
switch (AF.getValueSize()) {
default:
assert(0 && "Invalid size!");
case 1: OW->Write8 (uint8_t (AF.getValue())); break;
case 2: OW->Write16(uint16_t(AF.getValue())); break;
case 4: OW->Write32(uint32_t(AF.getValue())); break;
case 8: OW->Write64(uint64_t(AF.getValue())); break;
}
}
break;
}
case MCFragment::FT_Data: {
MCDataFragment &DF = cast<MCDataFragment>(F);
assert(FragmentSize == DF.getContents().size() && "Invalid size!");
OW->WriteBytes(DF.getContents().str());
break;
}
case MCFragment::FT_Fill: {
MCFillFragment &FF = cast<MCFillFragment>(F);
assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
switch (FF.getValueSize()) {
default:
assert(0 && "Invalid size!");
case 1: OW->Write8 (uint8_t (FF.getValue())); break;
case 2: OW->Write16(uint16_t(FF.getValue())); break;
case 4: OW->Write32(uint32_t(FF.getValue())); break;
case 8: OW->Write64(uint64_t(FF.getValue())); break;
}
}
break;
}
case MCFragment::FT_Inst:
llvm_unreachable("unexpected inst fragment after lowering");
break;
case MCFragment::FT_Org: {
MCOrgFragment &OF = cast<MCOrgFragment>(F);
for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
OW->Write8(uint8_t(OF.getValue()));
break;
}
}
assert(OW->getStream().tell() - Start == FragmentSize);
}
void MCAssembler::WriteSectionData(const MCSectionData *SD,
const MCAsmLayout &Layout,
MCObjectWriter *OW) const {
// Ignore virtual sections.
if (getBackend().isVirtualSection(SD->getSection())) {
assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
// Check that contents are only things legal inside a virtual section.
for (MCSectionData::const_iterator it = SD->begin(),
ie = SD->end(); it != ie; ++it) {
switch (it->getKind()) {
default:
assert(0 && "Invalid fragment in virtual section!");
case MCFragment::FT_Align:
assert(!cast<MCAlignFragment>(it)->getValueSize() &&
"Invalid align in virtual section!");
break;
case MCFragment::FT_Fill:
assert(!cast<MCFillFragment>(it)->getValueSize() &&
"Invalid fill in virtual section!");
break;
}
}
return;
}
uint64_t Start = OW->getStream().tell();
(void) Start;
for (MCSectionData::const_iterator it = SD->begin(),
ie = SD->end(); it != ie; ++it)
WriteFragmentData(*this, Layout, *it, OW);
assert(OW->getStream().tell() - Start == Layout.getSectionFileSize(SD));
}
void MCAssembler::Finish() {
DEBUG_WITH_TYPE("mc-dump", {
llvm::errs() << "assembler backend - pre-layout\n--\n";
dump(); });
// Create the layout object.
MCAsmLayout Layout(*this);
// Insert additional align fragments for concrete sections to explicitly pad
// the previous section to match their alignment requirements. This is for
// 'gas' compatibility, it shouldn't strictly be necessary.
//
// FIXME: This may be Mach-O specific.
for (unsigned i = 1, e = Layout.getSectionOrder().size(); i < e; ++i) {
MCSectionData *SD = Layout.getSectionOrder()[i];
// Ignore sections without alignment requirements.
unsigned Align = SD->getAlignment();
if (Align <= 1)
continue;
// Ignore virtual sections, they don't cause file size modifications.
if (getBackend().isVirtualSection(SD->getSection()))
continue;
// Otherwise, create a new align fragment at the end of the previous
// section.
MCAlignFragment *AF = new MCAlignFragment(Align, 0, 1, Align,
Layout.getSectionOrder()[i - 1]);
AF->setOnlyAlignAddress(true);
}
// Create dummy fragments and assign section ordinals.
unsigned SectionIndex = 0;
for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
// Create dummy fragments to eliminate any empty sections, this simplifies
// layout.
if (it->getFragmentList().empty())
new MCFillFragment(0, 1, 0, it);
it->setOrdinal(SectionIndex++);
}
// Assign layout order indices to sections and fragments.
unsigned FragmentIndex = 0;
for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
MCSectionData *SD = Layout.getSectionOrder()[i];
SD->setLayoutOrder(i);
for (MCSectionData::iterator it2 = SD->begin(),
ie2 = SD->end(); it2 != ie2; ++it2)
it2->setLayoutOrder(FragmentIndex++);
}
// Layout until everything fits.
while (LayoutOnce(Layout))
continue;
DEBUG_WITH_TYPE("mc-dump", {
llvm::errs() << "assembler backend - post-relaxation\n--\n";
dump(); });
// Finalize the layout, including fragment lowering.
FinishLayout(Layout);
DEBUG_WITH_TYPE("mc-dump", {
llvm::errs() << "assembler backend - final-layout\n--\n";
dump(); });
uint64_t StartOffset = OS.tell();
llvm::OwningPtr<MCObjectWriter> Writer(getBackend().createObjectWriter(OS));
if (!Writer)
report_fatal_error("unable to create object writer!");
// Allow the object writer a chance to perform post-layout binding (for
// example, to set the index fields in the symbol data).
Writer->ExecutePostLayoutBinding(*this);
// Evaluate and apply the fixups, generating relocation entries as necessary.
for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
for (MCSectionData::iterator it2 = it->begin(),
ie2 = it->end(); it2 != ie2; ++it2) {
MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
if (!DF)
continue;
for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
MCFixup &Fixup = *it3;
// Evaluate the fixup.
MCValue Target;
uint64_t FixedValue;
if (!EvaluateFixup(Layout, Fixup, DF, Target, FixedValue)) {
// The fixup was unresolved, we need a relocation. Inform the object
// writer of the relocation, and give it an opportunity to adjust the
// fixup value if need be.
Writer->RecordRelocation(*this, Layout, DF, Fixup, Target,FixedValue);
}
getBackend().ApplyFixup(Fixup, *DF, FixedValue);
}
}
}
// Write the object file.
Writer->WriteObject(*this, Layout);
stats::ObjectBytes += OS.tell() - StartOffset;
}
bool MCAssembler::FixupNeedsRelaxation(const MCFixup &Fixup,
const MCFragment *DF,
const MCAsmLayout &Layout) const {
if (getRelaxAll())
return true;
// If we cannot resolve the fixup value, it requires relaxation.
MCValue Target;
uint64_t Value;
if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
return true;
// Otherwise, relax if the value is too big for a (signed) i8.
//
// FIXME: This is target dependent!
return int64_t(Value) != int64_t(int8_t(Value));
}
bool MCAssembler::FragmentNeedsRelaxation(const MCInstFragment *IF,
const MCAsmLayout &Layout) const {
// If this inst doesn't ever need relaxation, ignore it. This occurs when we
// are intentionally pushing out inst fragments, or because we relaxed a
// previous instruction to one that doesn't need relaxation.
if (!getBackend().MayNeedRelaxation(IF->getInst()))
return false;
for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
ie = IF->fixup_end(); it != ie; ++it)
if (FixupNeedsRelaxation(*it, IF, Layout))
return true;
return false;
}
bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
++stats::RelaxationSteps;
// Layout the sections in order.
Layout.LayoutFile();
// Scan for fragments that need relaxation.
bool WasRelaxed = false;
for (iterator it = begin(), ie = end(); it != ie; ++it) {
MCSectionData &SD = *it;
for (MCSectionData::iterator it2 = SD.begin(),
ie2 = SD.end(); it2 != ie2; ++it2) {
// Check if this is an instruction fragment that needs relaxation.
MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
if (!IF || !FragmentNeedsRelaxation(IF, Layout))
continue;
++stats::RelaxedInstructions;
// FIXME-PERF: We could immediately lower out instructions if we can tell
// they are fully resolved, to avoid retesting on later passes.
// Relax the fragment.
MCInst Relaxed;
getBackend().RelaxInstruction(IF->getInst(), Relaxed);
// Encode the new instruction.
//
// FIXME-PERF: If it matters, we could let the target do this. It can
// probably do so more efficiently in many cases.
SmallVector<MCFixup, 4> Fixups;
SmallString<256> Code;
raw_svector_ostream VecOS(Code);
getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
VecOS.flush();
// Update the instruction fragment.
int SlideAmount = Code.size() - IF->getInstSize();
IF->setInst(Relaxed);
IF->getCode() = Code;
IF->getFixups().clear();
// FIXME: Eliminate copy.
for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
IF->getFixups().push_back(Fixups[i]);
// Update the layout, and remember that we relaxed.
Layout.UpdateForSlide(IF, SlideAmount);
WasRelaxed = true;
}
}
return WasRelaxed;
}
void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
// Lower out any instruction fragments, to simplify the fixup application and
// output.
//
// FIXME-PERF: We don't have to do this, but the assumption is that it is
// cheap (we will mostly end up eliminating fragments and appending on to data
// fragments), so the extra complexity downstream isn't worth it. Evaluate
// this assumption.
for (iterator it = begin(), ie = end(); it != ie; ++it) {
MCSectionData &SD = *it;
for (MCSectionData::iterator it2 = SD.begin(),
ie2 = SD.end(); it2 != ie2; ++it2) {
MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
if (!IF)
continue;
// Create a new data fragment for the instruction.
//
// FIXME-PERF: Reuse previous data fragment if possible.
MCDataFragment *DF = new MCDataFragment();
SD.getFragmentList().insert(it2, DF);
// Update the data fragments layout data.
DF->setParent(IF->getParent());
DF->setAtom(IF->getAtom());
DF->setLayoutOrder(IF->getLayoutOrder());
Layout.FragmentReplaced(IF, DF);
// Copy in the data and the fixups.
DF->getContents().append(IF->getCode().begin(), IF->getCode().end());
for (unsigned i = 0, e = IF->getFixups().size(); i != e; ++i)
DF->getFixups().push_back(IF->getFixups()[i]);
// Delete the instruction fragment and update the iterator.
SD.getFragmentList().erase(IF);
it2 = DF;
}
}
}
// Debugging methods
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
OS << "<MCFixup" << " Offset:" << AF.getOffset()
<< " Value:" << *AF.getValue()
<< " Kind:" << AF.getKind() << ">";
return OS;
}
}
void MCFragment::dump() {
raw_ostream &OS = llvm::errs();
OS << "<";
switch (getKind()) {
case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
case MCFragment::FT_Data: OS << "MCDataFragment"; break;
case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
case MCFragment::FT_Inst: OS << "MCInstFragment"; break;
case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
}
OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
<< " Offset:" << Offset << " EffectiveSize:" << EffectiveSize << ">";
switch (getKind()) {
case MCFragment::FT_Align: {
const MCAlignFragment *AF = cast<MCAlignFragment>(this);
if (AF->hasEmitNops())
OS << " (emit nops)";
if (AF->hasOnlyAlignAddress())
OS << " (only align section)";
OS << "\n ";
OS << " Alignment:" << AF->getAlignment()
<< " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
<< " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
break;
}
case MCFragment::FT_Data: {
const MCDataFragment *DF = cast<MCDataFragment>(this);
OS << "\n ";
OS << " Contents:[";
const SmallVectorImpl<char> &Contents = DF->getContents();
for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
if (i) OS << ",";
OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
}
OS << "] (" << Contents.size() << " bytes)";
if (!DF->getFixups().empty()) {
OS << ",\n ";
OS << " Fixups:[";
for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
ie = DF->fixup_end(); it != ie; ++it) {
if (it != DF->fixup_begin()) OS << ",\n ";
OS << *it;
}
OS << "]";
}
break;
}
case MCFragment::FT_Fill: {
const MCFillFragment *FF = cast<MCFillFragment>(this);
OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
<< " Size:" << FF->getSize();
break;
}
case MCFragment::FT_Inst: {
const MCInstFragment *IF = cast<MCInstFragment>(this);
OS << "\n ";
OS << " Inst:";
IF->getInst().dump_pretty(OS);
break;
}
case MCFragment::FT_Org: {
const MCOrgFragment *OF = cast<MCOrgFragment>(this);
OS << "\n ";
OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
break;
}
}
OS << ">";
}
void MCSectionData::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCSectionData";
OS << " Alignment:" << getAlignment() << " Address:" << Address
<< " Fragments:[\n ";
for (iterator it = begin(), ie = end(); it != ie; ++it) {
if (it != begin()) OS << ",\n ";
it->dump();
}
OS << "]>";
}
void MCSymbolData::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCSymbolData Symbol:" << getSymbol()
<< " Fragment:" << getFragment() << " Offset:" << getOffset()
<< " Flags:" << getFlags() << " Index:" << getIndex();
if (isCommon())
OS << " (common, size:" << getCommonSize()
<< " align: " << getCommonAlignment() << ")";
if (isExternal())
OS << " (external)";
if (isPrivateExtern())
OS << " (private extern)";
OS << ">";
}
void MCAssembler::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCAssembler\n";
OS << " Sections:[\n ";
for (iterator it = begin(), ie = end(); it != ie; ++it) {
if (it != begin()) OS << ",\n ";
it->dump();
}
OS << "],\n";
OS << " Symbols:[";
for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
if (it != symbol_begin()) OS << ",\n ";
it->dump();
}
OS << "]>\n";
}
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