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llvm/lib/MC/MCAssembler.cpp
Rafael Espindola a23cc6a1ea Add r224985 back with fixes. 
The fixes are to note that AArch64 has additional restrictions on when local
relocations can be used. In particular, ld64 requires that relocations to
cstring/cfstrings use linker visible symbols.

Original message:

In an assembly expression like

bar:
  .long L0 + 1

the intended semantics is that bar will contain a pointer one byte past L0.

In sections that are merged by content (strings, 4 byte constants, etc), a
single position in the section doesn't give the linker enough information.
For example, it would not be able to tell a relocation must point to the
end of a string, since that would look just like the start of the next.

The solution used in ELF to use relocation with symbols if there is a non-zero
addend.

In MachO before this patch we would just keep all symbols in some sections.

This would miss some cases (only cstrings on x86_64 were implemented) and was
inefficient since most relocations have an addend of 0 and can be represented
without the symbol.

This patch implements the non-zero addend logic for MachO too.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226503 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-19 21:11:14 +00:00

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44 KiB
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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.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCAssembler.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/raw_ostream.h"
#include <tuple>
using namespace llvm;
#define DEBUG_TYPE "assembler"
namespace {
namespace stats {
STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
STATISTIC(EmittedRelaxableFragments,
"Number of emitted assembler fragments - relaxable");
STATISTIC(EmittedDataFragments,
"Number of emitted assembler fragments - data");
STATISTIC(EmittedCompactEncodedInstFragments,
"Number of emitted assembler fragments - compact encoded inst");
STATISTIC(EmittedAlignFragments,
"Number of emitted assembler fragments - align");
STATISTIC(EmittedFillFragments,
"Number of emitted assembler fragments - fill");
STATISTIC(EmittedOrgFragments,
"Number of emitted assembler fragments - org");
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");
}
}
// 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()
{
// Compute the section layout order. Virtual sections must go last.
for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
if (!it->getSection().isVirtualSection())
SectionOrder.push_back(&*it);
for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
if (it->getSection().isVirtualSection())
SectionOrder.push_back(&*it);
}
bool MCAsmLayout::isFragmentValid(const MCFragment *F) const {
const MCSectionData &SD = *F->getParent();
const MCFragment *LastValid = LastValidFragment.lookup(&SD);
if (!LastValid)
return false;
assert(LastValid->getParent() == F->getParent());
return F->getLayoutOrder() <= LastValid->getLayoutOrder();
}
void MCAsmLayout::invalidateFragmentsFrom(MCFragment *F) {
// If this fragment wasn't already valid, we don't need to do anything.
if (!isFragmentValid(F))
return;
// Otherwise, reset the last valid fragment to the previous fragment
// (if this is the first fragment, it will be NULL).
const MCSectionData &SD = *F->getParent();
LastValidFragment[&SD] = F->getPrevNode();
}
void MCAsmLayout::ensureValid(const MCFragment *F) const {
MCSectionData &SD = *F->getParent();
MCFragment *Cur = LastValidFragment[&SD];
if (!Cur)
Cur = &*SD.begin();
else
Cur = Cur->getNextNode();
// Advance the layout position until the fragment is valid.
while (!isFragmentValid(F)) {
assert(Cur && "Layout bookkeeping error");
const_cast<MCAsmLayout*>(this)->layoutFragment(Cur);
Cur = Cur->getNextNode();
}
}
uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
ensureValid(F);
assert(F->Offset != ~UINT64_C(0) && "Address not set!");
return F->Offset;
}
// Simple getSymbolOffset helper for the non-varibale case.
static bool getLabelOffset(const MCAsmLayout &Layout, const MCSymbolData &SD,
bool ReportError, uint64_t &Val) {
if (!SD.getFragment()) {
if (ReportError)
report_fatal_error("unable to evaluate offset to undefined symbol '" +
SD.getSymbol().getName() + "'");
return false;
}
Val = Layout.getFragmentOffset(SD.getFragment()) + SD.getOffset();
return true;
}
static bool getSymbolOffsetImpl(const MCAsmLayout &Layout,
const MCSymbolData *SD, bool ReportError,
uint64_t &Val) {
const MCSymbol &S = SD->getSymbol();
if (!S.isVariable())
return getLabelOffset(Layout, *SD, ReportError, Val);
// If SD is a variable, evaluate it.
MCValue Target;
if (!S.getVariableValue()->EvaluateAsValue(Target, &Layout, nullptr))
report_fatal_error("unable to evaluate offset for variable '" +
S.getName() + "'");
uint64_t Offset = Target.getConstant();
const MCAssembler &Asm = Layout.getAssembler();
const MCSymbolRefExpr *A = Target.getSymA();
if (A) {
uint64_t ValA;
if (!getLabelOffset(Layout, Asm.getSymbolData(A->getSymbol()), ReportError,
ValA))
return false;
Offset += ValA;
}
const MCSymbolRefExpr *B = Target.getSymB();
if (B) {
uint64_t ValB;
if (!getLabelOffset(Layout, Asm.getSymbolData(B->getSymbol()), ReportError,
ValB))
return false;
Offset -= ValB;
}
Val = Offset;
return true;
}
bool MCAsmLayout::getSymbolOffset(const MCSymbolData *SD, uint64_t &Val) const {
return getSymbolOffsetImpl(*this, SD, false, Val);
}
uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
uint64_t Val;
getSymbolOffsetImpl(*this, SD, true, Val);
return Val;
}
const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
if (!Symbol.isVariable())
return &Symbol;
const MCExpr *Expr = Symbol.getVariableValue();
MCValue Value;
if (!Expr->EvaluateAsValue(Value, this, nullptr))
llvm_unreachable("Invalid Expression");
const MCSymbolRefExpr *RefB = Value.getSymB();
if (RefB)
Assembler.getContext().FatalError(
SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
"' could not be evaluated in a subtraction expression");
const MCSymbolRefExpr *A = Value.getSymA();
if (!A)
return nullptr;
const MCSymbol &ASym = A->getSymbol();
const MCAssembler &Asm = getAssembler();
const MCSymbolData &ASD = Asm.getSymbolData(ASym);
if (ASD.isCommon()) {
// FIXME: we should probably add a SMLoc to MCExpr.
Asm.getContext().FatalError(SMLoc(),
"Common symbol " + ASym.getName() +
" cannot be used in assignment expr");
}
return &ASym;
}
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) + getAssembler().computeFragmentSize(*this, F);
}
uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
// Virtual sections have no file size.
if (SD->getSection().isVirtualSection())
return 0;
// Otherwise, the file size is the same as the address space size.
return getSectionAddressSize(SD);
}
uint64_t MCAsmLayout::computeBundlePadding(const MCFragment *F,
uint64_t FOffset, uint64_t FSize) {
uint64_t BundleSize = Assembler.getBundleAlignSize();
assert(BundleSize > 0 &&
"computeBundlePadding should only be called if bundling is enabled");
uint64_t BundleMask = BundleSize - 1;
uint64_t OffsetInBundle = FOffset & BundleMask;
uint64_t EndOfFragment = OffsetInBundle + FSize;
// There are two kinds of bundling restrictions:
//
// 1) For alignToBundleEnd(), add padding to ensure that the fragment will
// *end* on a bundle boundary.
// 2) Otherwise, check if the fragment would cross a bundle boundary. If it
// would, add padding until the end of the bundle so that the fragment
// will start in a new one.
if (F->alignToBundleEnd()) {
// Three possibilities here:
//
// A) The fragment just happens to end at a bundle boundary, so we're good.
// B) The fragment ends before the current bundle boundary: pad it just
// enough to reach the boundary.
// C) The fragment ends after the current bundle boundary: pad it until it
// reaches the end of the next bundle boundary.
//
// Note: this code could be made shorter with some modulo trickery, but it's
// intentionally kept in its more explicit form for simplicity.
if (EndOfFragment == BundleSize)
return 0;
else if (EndOfFragment < BundleSize)
return BundleSize - EndOfFragment;
else { // EndOfFragment > BundleSize
return 2 * BundleSize - EndOfFragment;
}
} else if (EndOfFragment > BundleSize)
return BundleSize - OffsetInBundle;
else
return 0;
}
/* *** */
MCFragment::MCFragment() : Kind(FragmentType(~0)) {
}
MCFragment::~MCFragment() {
}
MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
: Kind(_Kind), Parent(_Parent), Atom(nullptr), Offset(~UINT64_C(0))
{
if (Parent)
Parent->getFragmentList().push_back(this);
}
/* *** */
MCEncodedFragment::~MCEncodedFragment() {
}
/* *** */
MCEncodedFragmentWithFixups::~MCEncodedFragmentWithFixups() {
}
/* *** */
MCSectionData::MCSectionData() : Section(nullptr) {}
MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
: Section(&_Section),
Ordinal(~UINT32_C(0)),
Alignment(1),
BundleLockState(NotBundleLocked),
BundleLockNestingDepth(0),
BundleGroupBeforeFirstInst(false),
HasInstructions(false)
{
if (A)
A->getSectionList().push_back(this);
}
MCSectionData::iterator
MCSectionData::getSubsectionInsertionPoint(unsigned Subsection) {
if (Subsection == 0 && SubsectionFragmentMap.empty())
return end();
SmallVectorImpl<std::pair<unsigned, MCFragment *> >::iterator MI =
std::lower_bound(SubsectionFragmentMap.begin(), SubsectionFragmentMap.end(),
std::make_pair(Subsection, (MCFragment *)nullptr));
bool ExactMatch = false;
if (MI != SubsectionFragmentMap.end()) {
ExactMatch = MI->first == Subsection;
if (ExactMatch)
++MI;
}
iterator IP;
if (MI == SubsectionFragmentMap.end())
IP = end();
else
IP = MI->second;
if (!ExactMatch && Subsection != 0) {
// The GNU as documentation claims that subsections have an alignment of 4,
// although this appears not to be the case.
MCFragment *F = new MCDataFragment();
SubsectionFragmentMap.insert(MI, std::make_pair(Subsection, F));
getFragmentList().insert(IP, F);
F->setParent(this);
}
return IP;
}
void MCSectionData::setBundleLockState(BundleLockStateType NewState) {
if (NewState == NotBundleLocked) {
if (BundleLockNestingDepth == 0) {
report_fatal_error("Mismatched bundle_lock/unlock directives");
}
if (--BundleLockNestingDepth == 0) {
BundleLockState = NotBundleLocked;
}
return;
}
// If any of the directives is an align_to_end directive, the whole nested
// group is align_to_end. So don't downgrade from align_to_end to just locked.
if (BundleLockState != BundleLockedAlignToEnd) {
BundleLockState = NewState;
}
++BundleLockNestingDepth;
}
/* *** */
MCSymbolData::MCSymbolData() : Symbol(nullptr) {}
MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
uint64_t _Offset, MCAssembler *A)
: Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
SymbolSize(nullptr), CommonAlign(-1U), Flags(0), Index(0) {
if (A)
A->getSymbolList().push_back(this);
}
/* *** */
MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
raw_ostream &OS_)
: Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
OS(OS_), BundleAlignSize(0), RelaxAll(false),
SubsectionsViaSymbols(false), ELFHeaderEFlags(0) {
VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
}
MCAssembler::~MCAssembler() {
}
void MCAssembler::reset() {
Sections.clear();
Symbols.clear();
SectionMap.clear();
SymbolMap.clear();
IndirectSymbols.clear();
DataRegions.clear();
LinkerOptions.clear();
FileNames.clear();
ThumbFuncs.clear();
BundleAlignSize = 0;
RelaxAll = false;
SubsectionsViaSymbols = false;
ELFHeaderEFlags = 0;
LOHContainer.reset();
VersionMinInfo.Major = 0;
// reset objects owned by us
getBackend().reset();
getEmitter().reset();
getWriter().reset();
getLOHContainer().reset();
}
bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
if (ThumbFuncs.count(Symbol))
return true;
if (!Symbol->isVariable())
return false;
// FIXME: It looks like gas supports some cases of the form "foo + 2". It
// is not clear if that is a bug or a feature.
const MCExpr *Expr = Symbol->getVariableValue();
const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr);
if (!Ref)
return false;
if (Ref->getKind() != MCSymbolRefExpr::VK_None)
return false;
const MCSymbol &Sym = Ref->getSymbol();
if (!isThumbFunc(&Sym))
return false;
ThumbFuncs.insert(Symbol); // Cache it.
return true;
}
void MCAssembler::addLocalUsedInReloc(const MCSymbol &Sym) {
assert(Sym.isTemporary());
LocalsUsedInReloc.insert(&Sym);
}
bool MCAssembler::isLocalUsedInReloc(const MCSymbol &Sym) const {
assert(Sym.isTemporary());
return LocalsUsedInReloc.count(&Sym);
}
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;
if (isLocalUsedInReloc(Symbol))
return true;
return false;
}
const MCSymbolData *MCAssembler::getAtom(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 nullptr;
// Non-linker visible symbols in sections which can't be atomized have no
// defining atom.
if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
SD->getFragment()->getParent()->getSection()))
return nullptr;
// Otherwise, return the atom for the containing fragment.
return SD->getFragment()->getAtom();
}
// Try to fully compute Expr to an absolute value and if that fails produce
// a relocatable expr.
// FIXME: Should this be the behavior of EvaluateAsRelocatable itself?
static bool evaluate(const MCExpr &Expr, const MCAsmLayout &Layout,
const MCFixup &Fixup, MCValue &Target) {
if (Expr.EvaluateAsValue(Target, &Layout, &Fixup)) {
if (Target.isAbsolute())
return true;
}
return Expr.EvaluateAsRelocatable(Target, &Layout, &Fixup);
}
bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
const MCFixup &Fixup, const MCFragment *DF,
MCValue &Target, uint64_t &Value) const {
++stats::evaluateFixup;
// FIXME: This code has some duplication with RecordRelocation. We should
// probably merge the two into a single callback that tries to evaluate a
// fixup and records a relocation if one is needed.
const MCExpr *Expr = Fixup.getValue();
if (!evaluate(*Expr, Layout, Fixup, Target))
getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
bool IsPCRel = Backend.getFixupKindInfo(
Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
bool IsResolved;
if (IsPCRel) {
if (Target.getSymB()) {
IsResolved = false;
} else if (!Target.getSymA()) {
IsResolved = false;
} else {
const MCSymbolRefExpr *A = Target.getSymA();
const MCSymbol &SA = A->getSymbol();
if (A->getKind() != MCSymbolRefExpr::VK_None ||
SA.AliasedSymbol().isUndefined()) {
IsResolved = false;
} else {
const MCSymbolData &DataA = getSymbolData(SA);
IsResolved =
getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
*DF, false, true);
}
}
} else {
IsResolved = Target.isAbsolute();
}
Value = Target.getConstant();
if (const MCSymbolRefExpr *A = Target.getSymA()) {
const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
if (Sym.isDefined())
Value += Layout.getSymbolOffset(&getSymbolData(Sym));
}
if (const MCSymbolRefExpr *B = Target.getSymB()) {
const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
if (Sym.isDefined())
Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
}
bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
assert((ShouldAlignPC ? IsPCRel : true) &&
"FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
if (IsPCRel) {
uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
// A number of ARM fixups in Thumb mode require that the effective PC
// address be determined as the 32-bit aligned version of the actual offset.
if (ShouldAlignPC) Offset &= ~0x3;
Value -= Offset;
}
// Let the backend adjust the fixup value if necessary, including whether
// we need a relocation.
Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
IsResolved);
return IsResolved;
}
uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
const MCFragment &F) const {
switch (F.getKind()) {
case MCFragment::FT_Data:
case MCFragment::FT_Relaxable:
case MCFragment::FT_CompactEncodedInst:
return cast<MCEncodedFragment>(F).getContents().size();
case MCFragment::FT_Fill:
return cast<MCFillFragment>(F).getSize();
case MCFragment::FT_LEB:
return cast<MCLEBFragment>(F).getContents().size();
case MCFragment::FT_Align: {
const MCAlignFragment &AF = cast<MCAlignFragment>(F);
unsigned Offset = Layout.getFragmentOffset(&AF);
unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
// If we are padding with nops, force the padding to be larger than the
// minimum nop size.
if (Size > 0 && AF.hasEmitNops()) {
while (Size % getBackend().getMinimumNopSize())
Size += AF.getAlignment();
}
if (Size > AF.getMaxBytesToEmit())
return 0;
return Size;
}
case MCFragment::FT_Org: {
const MCOrgFragment &OF = cast<MCOrgFragment>(F);
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.
uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
int64_t Size = TargetLocation - FragmentOffset;
if (Size < 0 || Size >= 0x40000000)
report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
"' (at offset '" + Twine(FragmentOffset) + "')");
return Size;
}
case MCFragment::FT_Dwarf:
return cast<MCDwarfLineAddrFragment>(F).getContents().size();
case MCFragment::FT_DwarfFrame:
return cast<MCDwarfCallFrameFragment>(F).getContents().size();
}
llvm_unreachable("invalid fragment kind");
}
void MCAsmLayout::layoutFragment(MCFragment *F) {
MCFragment *Prev = F->getPrevNode();
// We should never try to recompute something which is valid.
assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
// We should never try to compute the fragment layout if its predecessor
// isn't valid.
assert((!Prev || isFragmentValid(Prev)) &&
"Attempt to compute fragment before its predecessor!");
++stats::FragmentLayouts;
// Compute fragment offset and size.
if (Prev)
F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
else
F->Offset = 0;
LastValidFragment[F->getParent()] = F;
// If bundling is enabled and this fragment has instructions in it, it has to
// obey the bundling restrictions. With padding, we'll have:
//
//
// BundlePadding
// |||
// -------------------------------------
// Prev |##########| F |
// -------------------------------------
// ^
// |
// F->Offset
//
// The fragment's offset will point to after the padding, and its computed
// size won't include the padding.
//
if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
assert(isa<MCEncodedFragment>(F) &&
"Only MCEncodedFragment implementations have instructions");
uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
if (FSize > Assembler.getBundleAlignSize())
report_fatal_error("Fragment can't be larger than a bundle size");
uint64_t RequiredBundlePadding = computeBundlePadding(F, F->Offset, FSize);
if (RequiredBundlePadding > UINT8_MAX)
report_fatal_error("Padding cannot exceed 255 bytes");
F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
F->Offset += RequiredBundlePadding;
}
}
/// \brief Write the contents of a fragment to the given object writer. Expects
/// a MCEncodedFragment.
static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
const MCEncodedFragment &EF = cast<MCEncodedFragment>(F);
OW->WriteBytes(EF.getContents());
}
/// \brief Write the fragment \p F to the output file.
static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment &F) {
MCObjectWriter *OW = &Asm.getWriter();
// FIXME: Embed in fragments instead?
uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
// Should NOP padding be written out before this fragment?
unsigned BundlePadding = F.getBundlePadding();
if (BundlePadding > 0) {
assert(Asm.isBundlingEnabled() &&
"Writing bundle padding with disabled bundling");
assert(F.hasInstructions() &&
"Writing bundle padding for a fragment without instructions");
unsigned TotalLength = BundlePadding + static_cast<unsigned>(FragmentSize);
if (F.alignToBundleEnd() && TotalLength > Asm.getBundleAlignSize()) {
// If the padding itself crosses a bundle boundary, it must be emitted
// in 2 pieces, since even nop instructions must not cross boundaries.
// v--------------v <- BundleAlignSize
// v---------v <- BundlePadding
// ----------------------------
// | Prev |####|####| F |
// ----------------------------
// ^-------------------^ <- TotalLength
unsigned DistanceToBoundary = TotalLength - Asm.getBundleAlignSize();
if (!Asm.getBackend().writeNopData(DistanceToBoundary, OW))
report_fatal_error("unable to write NOP sequence of " +
Twine(DistanceToBoundary) + " bytes");
BundlePadding -= DistanceToBoundary;
}
if (!Asm.getBackend().writeNopData(BundlePadding, OW))
report_fatal_error("unable to write NOP sequence of " +
Twine(BundlePadding) + " bytes");
}
// This variable (and its dummy usage) is to participate in the assert at
// the end of the function.
uint64_t Start = OW->getStream().tell();
(void) Start;
++stats::EmittedFragments;
switch (F.getKind()) {
case MCFragment::FT_Align: {
++stats::EmittedAlignFragments;
const MCAlignFragment &AF = cast<MCAlignFragment>(F);
assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
uint64_t Count = FragmentSize / AF.getValueSize();
// 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 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: llvm_unreachable("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:
++stats::EmittedDataFragments;
writeFragmentContents(F, OW);
break;
case MCFragment::FT_Relaxable:
++stats::EmittedRelaxableFragments;
writeFragmentContents(F, OW);
break;
case MCFragment::FT_CompactEncodedInst:
++stats::EmittedCompactEncodedInstFragments;
writeFragmentContents(F, OW);
break;
case MCFragment::FT_Fill: {
++stats::EmittedFillFragments;
const 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: llvm_unreachable("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_LEB: {
const MCLEBFragment &LF = cast<MCLEBFragment>(F);
OW->WriteBytes(LF.getContents().str());
break;
}
case MCFragment::FT_Org: {
++stats::EmittedOrgFragments;
const MCOrgFragment &OF = cast<MCOrgFragment>(F);
for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
OW->Write8(uint8_t(OF.getValue()));
break;
}
case MCFragment::FT_Dwarf: {
const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
OW->WriteBytes(OF.getContents().str());
break;
}
case MCFragment::FT_DwarfFrame: {
const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
OW->WriteBytes(CF.getContents().str());
break;
}
}
assert(OW->getStream().tell() - Start == FragmentSize &&
"The stream should advance by fragment size");
}
void MCAssembler::writeSectionData(const MCSectionData *SD,
const MCAsmLayout &Layout) const {
// Ignore virtual sections.
if (SD->getSection().isVirtualSection()) {
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: llvm_unreachable("Invalid fragment in virtual section!");
case MCFragment::FT_Data: {
// Check that we aren't trying to write a non-zero contents (or fixups)
// into a virtual section. This is to support clients which use standard
// directives to fill the contents of virtual sections.
const MCDataFragment &DF = cast<MCDataFragment>(*it);
assert(DF.fixup_begin() == DF.fixup_end() &&
"Cannot have fixups in virtual section!");
for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
if (DF.getContents()[i]) {
if (auto *ELFSec = dyn_cast<const MCSectionELF>(&SD->getSection()))
report_fatal_error("non-zero initializer found in section '" +
ELFSec->getSectionName() + "'");
else
report_fatal_error("non-zero initializer found in virtual section");
}
break;
}
case MCFragment::FT_Align:
// Check that we aren't trying to write a non-zero value into a virtual
// section.
assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
cast<MCAlignFragment>(it)->getValue() == 0) &&
"Invalid align in virtual section!");
break;
case MCFragment::FT_Fill:
assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
cast<MCFillFragment>(it)->getValue() == 0) &&
"Invalid fill in virtual section!");
break;
}
}
return;
}
uint64_t Start = getWriter().getStream().tell();
(void)Start;
for (MCSectionData::const_iterator it = SD->begin(), ie = SD->end();
it != ie; ++it)
writeFragment(*this, Layout, *it);
assert(getWriter().getStream().tell() - Start ==
Layout.getSectionAddressSize(SD));
}
std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
MCFragment &F,
const MCFixup &Fixup) {
// Evaluate the fixup.
MCValue Target;
uint64_t FixedValue;
bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
MCFixupKindInfo::FKF_IsPCRel;
if (!evaluateFixup(Layout, Fixup, &F, 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.
getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
FixedValue);
}
return std::make_pair(FixedValue, IsPCRel);
}
void MCAssembler::Finish() {
DEBUG_WITH_TYPE("mc-dump", {
llvm::errs() << "assembler backend - pre-layout\n--\n";
dump(); });
// Create the layout object.
MCAsmLayout Layout(*this);
// 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 MCDataFragment(it);
it->setOrdinal(SectionIndex++);
}
// Assign layout order indices to sections and fragments.
for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
MCSectionData *SD = Layout.getSectionOrder()[i];
SD->setLayoutOrder(i);
unsigned FragmentIndex = 0;
for (MCSectionData::iterator iFrag = SD->begin(), iFragEnd = SD->end();
iFrag != iFragEnd; ++iFrag)
iFrag->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();
// Allow the object writer a chance to perform post-layout binding (for
// example, to set the index fields in the symbol data).
getWriter().ExecutePostLayoutBinding(*this, Layout);
// 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) {
MCEncodedFragmentWithFixups *F =
dyn_cast<MCEncodedFragmentWithFixups>(it2);
if (F) {
for (MCEncodedFragmentWithFixups::fixup_iterator it3 = F->fixup_begin(),
ie3 = F->fixup_end(); it3 != ie3; ++it3) {
MCFixup &Fixup = *it3;
uint64_t FixedValue;
bool IsPCRel;
std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
getBackend().applyFixup(Fixup, F->getContents().data(),
F->getContents().size(), FixedValue, IsPCRel);
}
}
}
}
// Write the object file.
getWriter().WriteObject(*this, Layout);
stats::ObjectBytes += OS.tell() - StartOffset;
}
bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
const MCRelaxableFragment *DF,
const MCAsmLayout &Layout) const {
// If we cannot resolve the fixup value, it requires relaxation.
MCValue Target;
uint64_t Value;
if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
return true;
return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
}
bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
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(F->getInst()))
return false;
for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
ie = F->fixup_end(); it != ie; ++it)
if (fixupNeedsRelaxation(*it, F, Layout))
return true;
return false;
}
bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
MCRelaxableFragment &F) {
if (!fragmentNeedsRelaxation(&F, Layout))
return false;
++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(F.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, F.getSubtargetInfo());
VecOS.flush();
// Update the fragment.
F.setInst(Relaxed);
F.getContents() = Code;
F.getFixups() = Fixups;
return true;
}
bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
uint64_t OldSize = LF.getContents().size();
int64_t Value = LF.getValue().evaluateKnownAbsolute(Layout);
SmallString<8> &Data = LF.getContents();
Data.clear();
raw_svector_ostream OSE(Data);
if (LF.isSigned())
encodeSLEB128(Value, OSE);
else
encodeULEB128(Value, OSE);
OSE.flush();
return OldSize != LF.getContents().size();
}
bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
MCDwarfLineAddrFragment &DF) {
MCContext &Context = Layout.getAssembler().getContext();
uint64_t OldSize = DF.getContents().size();
int64_t AddrDelta = DF.getAddrDelta().evaluateKnownAbsolute(Layout);
int64_t LineDelta;
LineDelta = DF.getLineDelta();
SmallString<8> &Data = DF.getContents();
Data.clear();
raw_svector_ostream OSE(Data);
MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
OSE.flush();
return OldSize != Data.size();
}
bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
MCDwarfCallFrameFragment &DF) {
MCContext &Context = Layout.getAssembler().getContext();
uint64_t OldSize = DF.getContents().size();
int64_t AddrDelta = DF.getAddrDelta().evaluateKnownAbsolute(Layout);
SmallString<8> &Data = DF.getContents();
Data.clear();
raw_svector_ostream OSE(Data);
MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
OSE.flush();
return OldSize != Data.size();
}
bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSectionData &SD) {
// Holds the first fragment which needed relaxing during this layout. It will
// remain NULL if none were relaxed.
// When a fragment is relaxed, all the fragments following it should get
// invalidated because their offset is going to change.
MCFragment *FirstRelaxedFragment = nullptr;
// Attempt to relax all the fragments in the section.
for (MCSectionData::iterator I = SD.begin(), IE = SD.end(); I != IE; ++I) {
// Check if this is a fragment that needs relaxation.
bool RelaxedFrag = false;
switch(I->getKind()) {
default:
break;
case MCFragment::FT_Relaxable:
assert(!getRelaxAll() &&
"Did not expect a MCRelaxableFragment in RelaxAll mode");
RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
break;
case MCFragment::FT_Dwarf:
RelaxedFrag = relaxDwarfLineAddr(Layout,
*cast<MCDwarfLineAddrFragment>(I));
break;
case MCFragment::FT_DwarfFrame:
RelaxedFrag =
relaxDwarfCallFrameFragment(Layout,
*cast<MCDwarfCallFrameFragment>(I));
break;
case MCFragment::FT_LEB:
RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
break;
}
if (RelaxedFrag && !FirstRelaxedFragment)
FirstRelaxedFragment = I;
}
if (FirstRelaxedFragment) {
Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
return true;
}
return false;
}
bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
++stats::RelaxationSteps;
bool WasRelaxed = false;
for (iterator it = begin(), ie = end(); it != ie; ++it) {
MCSectionData &SD = *it;
while (layoutSectionOnce(Layout, SD))
WasRelaxed = true;
}
return WasRelaxed;
}
void MCAssembler::finishLayout(MCAsmLayout &Layout) {
// The layout is done. Mark every fragment as valid.
for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
}
}
// 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;
}
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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_CompactEncodedInst:
OS << "MCCompactEncodedInstFragment"; break;
case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
}
OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
<< " Offset:" << Offset
<< " HasInstructions:" << hasInstructions()
<< " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
switch (getKind()) {
case MCFragment::FT_Align: {
const MCAlignFragment *AF = cast<MCAlignFragment>(this);
if (AF->hasEmitNops())
OS << " (emit nops)";
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->fixup_begin() != DF->fixup_end()) {
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_CompactEncodedInst: {
const MCCompactEncodedInstFragment *CEIF =
cast<MCCompactEncodedInstFragment>(this);
OS << "\n ";
OS << " Contents:[";
const SmallVectorImpl<char> &Contents = CEIF->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)";
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_Relaxable: {
const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
OS << "\n ";
OS << " Inst:";
F->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;
}
case MCFragment::FT_Dwarf: {
const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
OS << "\n ";
OS << " AddrDelta:" << OF->getAddrDelta()
<< " LineDelta:" << OF->getLineDelta();
break;
}
case MCFragment::FT_DwarfFrame: {
const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
OS << "\n ";
OS << " AddrDelta:" << CF->getAddrDelta();
break;
}
case MCFragment::FT_LEB: {
const MCLEBFragment *LF = cast<MCLEBFragment>(this);
OS << "\n ";
OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
break;
}
}
OS << ">";
}
void MCSectionData::dump() {
raw_ostream &OS = llvm::errs();
OS << "<MCSectionData";
OS << " Alignment:" << getAlignment()
<< " Fragments:[\n ";
for (iterator it = begin(), ie = end(); it != ie; ++it) {
if (it != begin()) OS << ",\n ";
it->dump();
}
OS << "]>";
}
void MCSymbolData::dump() const {
raw_ostream &OS = llvm::errs();
OS << "<MCSymbolData Symbol:" << getSymbol()
<< " Fragment:" << getFragment();
if (!isCommon())
OS << " Offset:" << getOffset();
OS << " 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";
}
#endif
// anchors for MC*Fragment vtables
void MCEncodedFragment::anchor() { }
void MCEncodedFragmentWithFixups::anchor() { }
void MCDataFragment::anchor() { }
void MCCompactEncodedInstFragment::anchor() { }
void MCRelaxableFragment::anchor() { }
void MCAlignFragment::anchor() { }
void MCFillFragment::anchor() { }
void MCOrgFragment::anchor() { }
void MCLEBFragment::anchor() { }
void MCDwarfLineAddrFragment::anchor() { }
void MCDwarfCallFrameFragment::anchor() { }
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