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llvm-mirror/lib/MC/MCAssembler.cpp
Shengchen Kan 3cf423c123 [MC] Simplify the logic of applying fixup for fragments, NFCI 
Replace mutiple `if else`  clauses with a `switch` clause and remove redundant checks. Before this patch, we need to add a statement like `if(!isa<MCxxxFragment>(Frag)) `  here each time we add a new kind of `MCEncodedFragment` even if it has no fixups. After this patch, we don't need to do that.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D83366
2020-07-09 16:39:13 +08:00

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//===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCAssembler.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringRef.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/MCCodeView.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCFragment.h"
#include "llvm/MC/MCInst.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/Alignment.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/EndianStream.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdint>
#include <cstring>
#include <tuple>
#include <utility>
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");
} // end namespace stats
} // end anonymous namespace
// 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.
/* *** */
MCAssembler::MCAssembler(MCContext &Context,
std::unique_ptr<MCAsmBackend> Backend,
std::unique_ptr<MCCodeEmitter> Emitter,
std::unique_ptr<MCObjectWriter> Writer)
: Context(Context), Backend(std::move(Backend)),
Emitter(std::move(Emitter)), Writer(std::move(Writer)),
BundleAlignSize(0), RelaxAll(false), SubsectionsViaSymbols(false),
IncrementalLinkerCompatible(false), ELFHeaderEFlags(0) {
VersionInfo.Major = 0; // Major version == 0 for "none specified"
}
MCAssembler::~MCAssembler() = default;
void MCAssembler::reset() {
Sections.clear();
Symbols.clear();
IndirectSymbols.clear();
DataRegions.clear();
LinkerOptions.clear();
FileNames.clear();
ThumbFuncs.clear();
BundleAlignSize = 0;
RelaxAll = false;
SubsectionsViaSymbols = false;
IncrementalLinkerCompatible = false;
ELFHeaderEFlags = 0;
LOHContainer.reset();
VersionInfo.Major = 0;
VersionInfo.SDKVersion = VersionTuple();
// reset objects owned by us
if (getBackendPtr())
getBackendPtr()->reset();
if (getEmitterPtr())
getEmitterPtr()->reset();
if (getWriterPtr())
getWriterPtr()->reset();
getLOHContainer().reset();
}
bool MCAssembler::registerSection(MCSection &Section) {
if (Section.isRegistered())
return false;
Sections.push_back(&Section);
Section.setIsRegistered(true);
return true;
}
bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
if (ThumbFuncs.count(Symbol))
return true;
if (!Symbol->isVariable())
return false;
const MCExpr *Expr = Symbol->getVariableValue();
MCValue V;
if (!Expr->evaluateAsRelocatable(V, nullptr, nullptr))
return false;
if (V.getSymB() || V.getRefKind() != MCSymbolRefExpr::VK_None)
return false;
const MCSymbolRefExpr *Ref = V.getSymA();
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;
}
bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
// Non-temporary labels should always be visible to the linker.
if (!Symbol.isTemporary())
return true;
if (Symbol.isUsedInReloc())
return true;
return false;
}
const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
// Linker visible symbols define atoms.
if (isSymbolLinkerVisible(S))
return &S;
// Absolute and undefined symbols have no defining atom.
if (!S.isInSection())
return nullptr;
// Non-linker visible symbols in sections which can't be atomized have no
// defining atom.
if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
*S.getFragment()->getParent()))
return nullptr;
// Otherwise, return the atom for the containing fragment.
return S.getFragment()->getAtom();
}
bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
const MCFixup &Fixup, const MCFragment *DF,
MCValue &Target, uint64_t &Value,
bool &WasForced) 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.
// On error claim to have completely evaluated the fixup, to prevent any
// further processing from being done.
const MCExpr *Expr = Fixup.getValue();
MCContext &Ctx = getContext();
Value = 0;
WasForced = false;
if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup)) {
Ctx.reportError(Fixup.getLoc(), "expected relocatable expression");
return true;
}
if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
if (RefB->getKind() != MCSymbolRefExpr::VK_None) {
Ctx.reportError(Fixup.getLoc(),
"unsupported subtraction of qualified symbol");
return true;
}
}
assert(getBackendPtr() && "Expected assembler backend");
bool IsTarget = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
MCFixupKindInfo::FKF_IsTarget;
if (IsTarget)
return getBackend().evaluateTargetFixup(*this, Layout, Fixup, DF, Target,
Value, WasForced);
unsigned FixupFlags = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags;
bool IsPCRel = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
MCFixupKindInfo::FKF_IsPCRel;
bool IsResolved = false;
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.isUndefined()) {
IsResolved = false;
} else if (auto *Writer = getWriterPtr()) {
IsResolved = (FixupFlags & MCFixupKindInfo::FKF_Constant) ||
Writer->isSymbolRefDifferenceFullyResolvedImpl(
*this, SA, *DF, false, true);
}
}
} else {
IsResolved = Target.isAbsolute();
}
Value = Target.getConstant();
if (const MCSymbolRefExpr *A = Target.getSymA()) {
const MCSymbol &Sym = A->getSymbol();
if (Sym.isDefined())
Value += Layout.getSymbolOffset(Sym);
}
if (const MCSymbolRefExpr *B = Target.getSymB()) {
const MCSymbol &Sym = B->getSymbol();
if (Sym.isDefined())
Value -= Layout.getSymbolOffset(Sym);
}
bool ShouldAlignPC = getBackend().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 force a relocation if needed.
if (IsResolved && getBackend().shouldForceRelocation(*this, Fixup, Target)) {
IsResolved = false;
WasForced = true;
}
return IsResolved;
}
uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
const MCFragment &F) const {
assert(getBackendPtr() && "Requires assembler backend");
switch (F.getKind()) {
case MCFragment::FT_Data:
return cast<MCDataFragment>(F).getContents().size();
case MCFragment::FT_Relaxable:
return cast<MCRelaxableFragment>(F).getContents().size();
case MCFragment::FT_CompactEncodedInst:
return cast<MCCompactEncodedInstFragment>(F).getContents().size();
case MCFragment::FT_Fill: {
auto &FF = cast<MCFillFragment>(F);
int64_t NumValues = 0;
if (!FF.getNumValues().evaluateAsAbsolute(NumValues, Layout)) {
getContext().reportError(FF.getLoc(),
"expected assembly-time absolute expression");
return 0;
}
int64_t Size = NumValues * FF.getValueSize();
if (Size < 0) {
getContext().reportError(FF.getLoc(), "invalid number of bytes");
return 0;
}
return Size;
}
case MCFragment::FT_LEB:
return cast<MCLEBFragment>(F).getContents().size();
case MCFragment::FT_BoundaryAlign:
return cast<MCBoundaryAlignFragment>(F).getSize();
case MCFragment::FT_SymbolId:
return 4;
case MCFragment::FT_Align: {
const MCAlignFragment &AF = cast<MCAlignFragment>(F);
unsigned Offset = Layout.getFragmentOffset(&AF);
unsigned Size = offsetToAlignment(Offset, Align(AF.getAlignment()));
// Insert extra Nops for code alignment if the target define
// shouldInsertExtraNopBytesForCodeAlign target hook.
if (AF.getParent()->UseCodeAlign() && AF.hasEmitNops() &&
getBackend().shouldInsertExtraNopBytesForCodeAlign(AF, Size))
return Size;
// 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);
MCValue Value;
if (!OF.getOffset().evaluateAsValue(Value, Layout)) {
getContext().reportError(OF.getLoc(),
"expected assembly-time absolute expression");
return 0;
}
uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
int64_t TargetLocation = Value.getConstant();
if (const MCSymbolRefExpr *A = Value.getSymA()) {
uint64_t Val;
if (!Layout.getSymbolOffset(A->getSymbol(), Val)) {
getContext().reportError(OF.getLoc(), "expected absolute expression");
return 0;
}
TargetLocation += Val;
}
int64_t Size = TargetLocation - FragmentOffset;
if (Size < 0 || Size >= 0x40000000) {
getContext().reportError(
OF.getLoc(), "invalid .org offset '" + Twine(TargetLocation) +
"' (at offset '" + Twine(FragmentOffset) + "')");
return 0;
}
return Size;
}
case MCFragment::FT_Dwarf:
return cast<MCDwarfLineAddrFragment>(F).getContents().size();
case MCFragment::FT_DwarfFrame:
return cast<MCDwarfCallFrameFragment>(F).getContents().size();
case MCFragment::FT_CVInlineLines:
return cast<MCCVInlineLineTableFragment>(F).getContents().size();
case MCFragment::FT_CVDefRange:
return cast<MCCVDefRangeFragment>(F).getContents().size();
case MCFragment::FT_Dummy:
llvm_unreachable("Should not have been added");
}
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!");
assert(!F->IsBeingLaidOut && "Already being laid out!");
F->IsBeingLaidOut = true;
++stats::FragmentLayouts;
// Compute fragment offset and size.
if (Prev)
F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
else
F->Offset = 0;
F->IsBeingLaidOut = false;
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.
//
// When the -mc-relax-all flag is used, we optimize bundling by writting the
// padding directly into fragments when the instructions are emitted inside
// the streamer. When the fragment is larger than the bundle size, we need to
// ensure that it's bundle aligned. This means that if we end up with
// multiple fragments, we must emit bundle padding between fragments.
//
// ".align N" is an example of a directive that introduces multiple
// fragments. We could add a special case to handle ".align N" by emitting
// within-fragment padding (which would produce less padding when N is less
// than the bundle size), but for now we don't.
//
if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
assert(isa<MCEncodedFragment>(F) &&
"Only MCEncodedFragment implementations have instructions");
MCEncodedFragment *EF = cast<MCEncodedFragment>(F);
uint64_t FSize = Assembler.computeFragmentSize(*this, *EF);
if (!Assembler.getRelaxAll() && FSize > Assembler.getBundleAlignSize())
report_fatal_error("Fragment can't be larger than a bundle size");
uint64_t RequiredBundlePadding =
computeBundlePadding(Assembler, EF, EF->Offset, FSize);
if (RequiredBundlePadding > UINT8_MAX)
report_fatal_error("Padding cannot exceed 255 bytes");
EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
EF->Offset += RequiredBundlePadding;
}
}
void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
bool New = !Symbol.isRegistered();
if (Created)
*Created = New;
if (New) {
Symbol.setIsRegistered(true);
Symbols.push_back(&Symbol);
}
}
void MCAssembler::writeFragmentPadding(raw_ostream &OS,
const MCEncodedFragment &EF,
uint64_t FSize) const {
assert(getBackendPtr() && "Expected assembler backend");
// Should NOP padding be written out before this fragment?
unsigned BundlePadding = EF.getBundlePadding();
if (BundlePadding > 0) {
assert(isBundlingEnabled() &&
"Writing bundle padding with disabled bundling");
assert(EF.hasInstructions() &&
"Writing bundle padding for a fragment without instructions");
unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
if (EF.alignToBundleEnd() && TotalLength > 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 - getBundleAlignSize();
if (!getBackend().writeNopData(OS, DistanceToBoundary))
report_fatal_error("unable to write NOP sequence of " +
Twine(DistanceToBoundary) + " bytes");
BundlePadding -= DistanceToBoundary;
}
if (!getBackend().writeNopData(OS, BundlePadding))
report_fatal_error("unable to write NOP sequence of " +
Twine(BundlePadding) + " bytes");
}
}
/// Write the fragment \p F to the output file.
static void writeFragment(raw_ostream &OS, const MCAssembler &Asm,
const MCAsmLayout &Layout, const MCFragment &F) {
// FIXME: Embed in fragments instead?
uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
support::endianness Endian = Asm.getBackend().Endian;
if (const MCEncodedFragment *EF = dyn_cast<MCEncodedFragment>(&F))
Asm.writeFragmentPadding(OS, *EF, FragmentSize);
// This variable (and its dummy usage) is to participate in the assert at
// the end of the function.
uint64_t Start = OS.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(OS, Count))
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: OS << char(AF.getValue()); break;
case 2:
support::endian::write<uint16_t>(OS, AF.getValue(), Endian);
break;
case 4:
support::endian::write<uint32_t>(OS, AF.getValue(), Endian);
break;
case 8:
support::endian::write<uint64_t>(OS, AF.getValue(), Endian);
break;
}
}
break;
}
case MCFragment::FT_Data:
++stats::EmittedDataFragments;
OS << cast<MCDataFragment>(F).getContents();
break;
case MCFragment::FT_Relaxable:
++stats::EmittedRelaxableFragments;
OS << cast<MCRelaxableFragment>(F).getContents();
break;
case MCFragment::FT_CompactEncodedInst:
++stats::EmittedCompactEncodedInstFragments;
OS << cast<MCCompactEncodedInstFragment>(F).getContents();
break;
case MCFragment::FT_Fill: {
++stats::EmittedFillFragments;
const MCFillFragment &FF = cast<MCFillFragment>(F);
uint64_t V = FF.getValue();
unsigned VSize = FF.getValueSize();
const unsigned MaxChunkSize = 16;
char Data[MaxChunkSize];
assert(0 < VSize && VSize <= MaxChunkSize && "Illegal fragment fill size");
// Duplicate V into Data as byte vector to reduce number of
// writes done. As such, do endian conversion here.
for (unsigned I = 0; I != VSize; ++I) {
unsigned index = Endian == support::little ? I : (VSize - I - 1);
Data[I] = uint8_t(V >> (index * 8));
}
for (unsigned I = VSize; I < MaxChunkSize; ++I)
Data[I] = Data[I - VSize];
// Set to largest multiple of VSize in Data.
const unsigned NumPerChunk = MaxChunkSize / VSize;
// Set ChunkSize to largest multiple of VSize in Data
const unsigned ChunkSize = VSize * NumPerChunk;
// Do copies by chunk.
StringRef Ref(Data, ChunkSize);
for (uint64_t I = 0, E = FragmentSize / ChunkSize; I != E; ++I)
OS << Ref;
// do remainder if needed.
unsigned TrailingCount = FragmentSize % ChunkSize;
if (TrailingCount)
OS.write(Data, TrailingCount);
break;
}
case MCFragment::FT_LEB: {
const MCLEBFragment &LF = cast<MCLEBFragment>(F);
OS << LF.getContents();
break;
}
case MCFragment::FT_BoundaryAlign: {
if (!Asm.getBackend().writeNopData(OS, FragmentSize))
report_fatal_error("unable to write nop sequence of " +
Twine(FragmentSize) + " bytes");
break;
}
case MCFragment::FT_SymbolId: {
const MCSymbolIdFragment &SF = cast<MCSymbolIdFragment>(F);
support::endian::write<uint32_t>(OS, SF.getSymbol()->getIndex(), Endian);
break;
}
case MCFragment::FT_Org: {
++stats::EmittedOrgFragments;
const MCOrgFragment &OF = cast<MCOrgFragment>(F);
for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
OS << char(OF.getValue());
break;
}
case MCFragment::FT_Dwarf: {
const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
OS << OF.getContents();
break;
}
case MCFragment::FT_DwarfFrame: {
const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
OS << CF.getContents();
break;
}
case MCFragment::FT_CVInlineLines: {
const auto &OF = cast<MCCVInlineLineTableFragment>(F);
OS << OF.getContents();
break;
}
case MCFragment::FT_CVDefRange: {
const auto &DRF = cast<MCCVDefRangeFragment>(F);
OS << DRF.getContents();
break;
}
case MCFragment::FT_Dummy:
llvm_unreachable("Should not have been added");
}
assert(OS.tell() - Start == FragmentSize &&
"The stream should advance by fragment size");
}
void MCAssembler::writeSectionData(raw_ostream &OS, const MCSection *Sec,
const MCAsmLayout &Layout) const {
assert(getBackendPtr() && "Expected assembler backend");
// Ignore virtual sections.
if (Sec->isVirtualSection()) {
assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
// Check that contents are only things legal inside a virtual section.
for (const MCFragment &F : *Sec) {
switch (F.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>(F);
if (DF.fixup_begin() != DF.fixup_end())
getContext().reportError(SMLoc(), Sec->getVirtualSectionKind() +
" section '" + Sec->getName() +
"' cannot have fixups");
for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
if (DF.getContents()[i]) {
getContext().reportError(SMLoc(),
Sec->getVirtualSectionKind() +
" section '" + Sec->getName() +
"' cannot have non-zero initializers");
break;
}
break;
}
case MCFragment::FT_Align:
// Check that we aren't trying to write a non-zero value into a virtual
// section.
assert((cast<MCAlignFragment>(F).getValueSize() == 0 ||
cast<MCAlignFragment>(F).getValue() == 0) &&
"Invalid align in virtual section!");
break;
case MCFragment::FT_Fill:
assert((cast<MCFillFragment>(F).getValue() == 0) &&
"Invalid fill in virtual section!");
break;
}
}
return;
}
uint64_t Start = OS.tell();
(void)Start;
for (const MCFragment &F : *Sec)
writeFragment(OS, *this, Layout, F);
assert(OS.tell() - Start == Layout.getSectionAddressSize(Sec));
}
std::tuple<MCValue, uint64_t, bool>
MCAssembler::handleFixup(const MCAsmLayout &Layout, MCFragment &F,
const MCFixup &Fixup) {
// Evaluate the fixup.
MCValue Target;
uint64_t FixedValue;
bool WasForced;
bool IsResolved = evaluateFixup(Layout, Fixup, &F, Target, FixedValue,
WasForced);
if (!IsResolved) {
// 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.
if (Target.getSymA() && Target.getSymB() &&
getBackend().requiresDiffExpressionRelocations()) {
// The fixup represents the difference between two symbols, which the
// backend has indicated must be resolved at link time. Split up the fixup
// into two relocations, one for the add, and one for the sub, and emit
// both of these. The constant will be associated with the add half of the
// expression.
MCFixup FixupAdd = MCFixup::createAddFor(Fixup);
MCValue TargetAdd =
MCValue::get(Target.getSymA(), nullptr, Target.getConstant());
getWriter().recordRelocation(*this, Layout, &F, FixupAdd, TargetAdd,
FixedValue);
MCFixup FixupSub = MCFixup::createSubFor(Fixup);
MCValue TargetSub = MCValue::get(Target.getSymB());
getWriter().recordRelocation(*this, Layout, &F, FixupSub, TargetSub,
FixedValue);
} else {
getWriter().recordRelocation(*this, Layout, &F, Fixup, Target,
FixedValue);
}
}
return std::make_tuple(Target, FixedValue, IsResolved);
}
void MCAssembler::layout(MCAsmLayout &Layout) {
assert(getBackendPtr() && "Expected assembler backend");
DEBUG_WITH_TYPE("mc-dump", {
errs() << "assembler backend - pre-layout\n--\n";
dump(); });
// Create dummy fragments and assign section ordinals.
unsigned SectionIndex = 0;
for (MCSection &Sec : *this) {
// Create dummy fragments to eliminate any empty sections, this simplifies
// layout.
if (Sec.getFragmentList().empty())
new MCDataFragment(&Sec);
Sec.setOrdinal(SectionIndex++);
}
// Assign layout order indices to sections and fragments.
for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
MCSection *Sec = Layout.getSectionOrder()[i];
Sec->setLayoutOrder(i);
unsigned FragmentIndex = 0;
for (MCFragment &Frag : *Sec)
Frag.setLayoutOrder(FragmentIndex++);
}
// Layout until everything fits.
while (layoutOnce(Layout)) {
if (getContext().hadError())
return;
// Size of fragments in one section can depend on the size of fragments in
// another. If any fragment has changed size, we have to re-layout (and
// as a result possibly further relax) all.
for (MCSection &Sec : *this)
Layout.invalidateFragmentsFrom(&*Sec.begin());
}
DEBUG_WITH_TYPE("mc-dump", {
errs() << "assembler backend - post-relaxation\n--\n";
dump(); });
// Finalize the layout, including fragment lowering.
finishLayout(Layout);
DEBUG_WITH_TYPE("mc-dump", {
errs() << "assembler backend - final-layout\n--\n";
dump(); });
// 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 (MCSection &Sec : *this) {
for (MCFragment &Frag : Sec) {
ArrayRef<MCFixup> Fixups;
MutableArrayRef<char> Contents;
const MCSubtargetInfo *STI = nullptr;
// Process MCAlignFragment and MCEncodedFragmentWithFixups here.
switch (Frag.getKind()) {
default:
continue;
case MCFragment::FT_Align: {
MCAlignFragment &AF = cast<MCAlignFragment>(Frag);
// Insert fixup type for code alignment if the target define
// shouldInsertFixupForCodeAlign target hook.
if (Sec.UseCodeAlign() && AF.hasEmitNops())
getBackend().shouldInsertFixupForCodeAlign(*this, Layout, AF);
continue;
}
case MCFragment::FT_Data: {
MCDataFragment &DF = cast<MCDataFragment>(Frag);
Fixups = DF.getFixups();
Contents = DF.getContents();
STI = DF.getSubtargetInfo();
assert(!DF.hasInstructions() || STI != nullptr);
break;
}
case MCFragment::FT_Relaxable: {
MCRelaxableFragment &RF = cast<MCRelaxableFragment>(Frag);
Fixups = RF.getFixups();
Contents = RF.getContents();
STI = RF.getSubtargetInfo();
assert(!RF.hasInstructions() || STI != nullptr);
break;
}
case MCFragment::FT_CVDefRange: {
MCCVDefRangeFragment &CF = cast<MCCVDefRangeFragment>(Frag);
Fixups = CF.getFixups();
Contents = CF.getContents();
break;
}
case MCFragment::FT_Dwarf: {
MCDwarfLineAddrFragment &DF = cast<MCDwarfLineAddrFragment>(Frag);
Fixups = DF.getFixups();
Contents = DF.getContents();
break;
}
case MCFragment::FT_DwarfFrame: {
MCDwarfCallFrameFragment &DF = cast<MCDwarfCallFrameFragment>(Frag);
Fixups = DF.getFixups();
Contents = DF.getContents();
break;
}
}
for (const MCFixup &Fixup : Fixups) {
uint64_t FixedValue;
bool IsResolved;
MCValue Target;
std::tie(Target, FixedValue, IsResolved) =
handleFixup(Layout, Frag, Fixup);
getBackend().applyFixup(*this, Fixup, Target, Contents, FixedValue,
IsResolved, STI);
}
}
}
}
void MCAssembler::Finish() {
// Create the layout object.
MCAsmLayout Layout(*this);
layout(Layout);
// Write the object file.
stats::ObjectBytes += getWriter().writeObject(*this, Layout);
}
bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
const MCRelaxableFragment *DF,
const MCAsmLayout &Layout) const {
assert(getBackendPtr() && "Expected assembler backend");
MCValue Target;
uint64_t Value;
bool WasForced;
bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value, WasForced);
if (Target.getSymA() &&
Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8 &&
Fixup.getKind() == FK_Data_1)
return false;
return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
Layout, WasForced);
}
bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
const MCAsmLayout &Layout) const {
assert(getBackendPtr() && "Expected assembler backend");
// 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(), *F->getSubtargetInfo()))
return false;
for (const MCFixup &Fixup : F->getFixups())
if (fixupNeedsRelaxation(Fixup, F, Layout))
return true;
return false;
}
bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
MCRelaxableFragment &F) {
assert(getEmitterPtr() &&
"Expected CodeEmitter defined for relaxInstruction");
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 = F.getInst();
getBackend().relaxInstruction(Relaxed, *F.getSubtargetInfo());
// 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());
// 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;
bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
if (!Abs)
report_fatal_error("sleb128 and uleb128 expressions must be absolute");
SmallString<8> &Data = LF.getContents();
Data.clear();
raw_svector_ostream OSE(Data);
// The compiler can generate EH table assembly that is impossible to assemble
// without either adding padding to an LEB fragment or adding extra padding
// to a later alignment fragment. To accommodate such tables, relaxation can
// only increase an LEB fragment size here, not decrease it. See PR35809.
if (LF.isSigned())
encodeSLEB128(Value, OSE, OldSize);
else
encodeULEB128(Value, OSE, OldSize);
return OldSize != LF.getContents().size();
}
/// Check if the branch crosses the boundary.
///
/// \param StartAddr start address of the fused/unfused branch.
/// \param Size size of the fused/unfused branch.
/// \param BoundaryAlignment alignment requirement of the branch.
/// \returns true if the branch cross the boundary.
static bool mayCrossBoundary(uint64_t StartAddr, uint64_t Size,
Align BoundaryAlignment) {
uint64_t EndAddr = StartAddr + Size;
return (StartAddr >> Log2(BoundaryAlignment)) !=
((EndAddr - 1) >> Log2(BoundaryAlignment));
}
/// Check if the branch is against the boundary.
///
/// \param StartAddr start address of the fused/unfused branch.
/// \param Size size of the fused/unfused branch.
/// \param BoundaryAlignment alignment requirement of the branch.
/// \returns true if the branch is against the boundary.
static bool isAgainstBoundary(uint64_t StartAddr, uint64_t Size,
Align BoundaryAlignment) {
uint64_t EndAddr = StartAddr + Size;
return (EndAddr & (BoundaryAlignment.value() - 1)) == 0;
}
/// Check if the branch needs padding.
///
/// \param StartAddr start address of the fused/unfused branch.
/// \param Size size of the fused/unfused branch.
/// \param BoundaryAlignment alignment requirement of the branch.
/// \returns true if the branch needs padding.
static bool needPadding(uint64_t StartAddr, uint64_t Size,
Align BoundaryAlignment) {
return mayCrossBoundary(StartAddr, Size, BoundaryAlignment) ||
isAgainstBoundary(StartAddr, Size, BoundaryAlignment);
}
bool MCAssembler::relaxBoundaryAlign(MCAsmLayout &Layout,
MCBoundaryAlignFragment &BF) {
// BoundaryAlignFragment that doesn't need to align any fragment should not be
// relaxed.
if (!BF.getLastFragment())
return false;
uint64_t AlignedOffset = Layout.getFragmentOffset(&BF);
uint64_t AlignedSize = 0;
for (const MCFragment *F = BF.getLastFragment(); F != &BF;
F = F->getPrevNode())
AlignedSize += computeFragmentSize(Layout, *F);
Align BoundaryAlignment = BF.getAlignment();
uint64_t NewSize = needPadding(AlignedOffset, AlignedSize, BoundaryAlignment)
? offsetToAlignment(AlignedOffset, BoundaryAlignment)
: 0U;
if (NewSize == BF.getSize())
return false;
BF.setSize(NewSize);
Layout.invalidateFragmentsFrom(&BF);
return true;
}
bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
MCDwarfLineAddrFragment &DF) {
MCContext &Context = Layout.getAssembler().getContext();
uint64_t OldSize = DF.getContents().size();
int64_t AddrDelta;
bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
assert(Abs && "We created a line delta with an invalid expression");
(void)Abs;
int64_t LineDelta;
LineDelta = DF.getLineDelta();
SmallVectorImpl<char> &Data = DF.getContents();
Data.clear();
raw_svector_ostream OSE(Data);
DF.getFixups().clear();
if (!getBackend().requiresDiffExpressionRelocations()) {
MCDwarfLineAddr::Encode(Context, getDWARFLinetableParams(), LineDelta,
AddrDelta, OSE);
} else {
uint32_t Offset;
uint32_t Size;
bool SetDelta = MCDwarfLineAddr::FixedEncode(Context,
getDWARFLinetableParams(),
LineDelta, AddrDelta,
OSE, &Offset, &Size);
// Add Fixups for address delta or new address.
const MCExpr *FixupExpr;
if (SetDelta) {
FixupExpr = &DF.getAddrDelta();
} else {
const MCBinaryExpr *ABE = cast<MCBinaryExpr>(&DF.getAddrDelta());
FixupExpr = ABE->getLHS();
}
DF.getFixups().push_back(
MCFixup::create(Offset, FixupExpr,
MCFixup::getKindForSize(Size, false /*isPCRel*/)));
}
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;
bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
assert(Abs && "We created call frame with an invalid expression");
(void) Abs;
SmallVectorImpl<char> &Data = DF.getContents();
Data.clear();
raw_svector_ostream OSE(Data);
DF.getFixups().clear();
if (getBackend().requiresDiffExpressionRelocations()) {
uint32_t Offset;
uint32_t Size;
MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE, &Offset,
&Size);
if (Size) {
DF.getFixups().push_back(MCFixup::create(
Offset, &DF.getAddrDelta(),
MCFixup::getKindForSizeInBits(Size /*In bits.*/, false /*isPCRel*/)));
}
} else {
MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
}
return OldSize != Data.size();
}
bool MCAssembler::relaxCVInlineLineTable(MCAsmLayout &Layout,
MCCVInlineLineTableFragment &F) {
unsigned OldSize = F.getContents().size();
getContext().getCVContext().encodeInlineLineTable(Layout, F);
return OldSize != F.getContents().size();
}
bool MCAssembler::relaxCVDefRange(MCAsmLayout &Layout,
MCCVDefRangeFragment &F) {
unsigned OldSize = F.getContents().size();
getContext().getCVContext().encodeDefRange(Layout, F);
return OldSize != F.getContents().size();
}
bool MCAssembler::relaxFragment(MCAsmLayout &Layout, MCFragment &F) {
switch(F.getKind()) {
default:
return false;
case MCFragment::FT_Relaxable:
assert(!getRelaxAll() &&
"Did not expect a MCRelaxableFragment in RelaxAll mode");
return relaxInstruction(Layout, cast<MCRelaxableFragment>(F));
case MCFragment::FT_Dwarf:
return relaxDwarfLineAddr(Layout, cast<MCDwarfLineAddrFragment>(F));
case MCFragment::FT_DwarfFrame:
return relaxDwarfCallFrameFragment(Layout,
cast<MCDwarfCallFrameFragment>(F));
case MCFragment::FT_LEB:
return relaxLEB(Layout, cast<MCLEBFragment>(F));
case MCFragment::FT_BoundaryAlign:
return relaxBoundaryAlign(Layout, cast<MCBoundaryAlignFragment>(F));
case MCFragment::FT_CVInlineLines:
return relaxCVInlineLineTable(Layout, cast<MCCVInlineLineTableFragment>(F));
case MCFragment::FT_CVDefRange:
return relaxCVDefRange(Layout, cast<MCCVDefRangeFragment>(F));
}
}
bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
// 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 (MCFragment &Frag : Sec) {
// Check if this is a fragment that needs relaxation.
bool RelaxedFrag = relaxFragment(Layout, Frag);
if (RelaxedFrag && !FirstRelaxedFragment)
FirstRelaxedFragment = &Frag;
}
if (FirstRelaxedFragment) {
Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
return true;
}
return false;
}
bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
++stats::RelaxationSteps;
bool WasRelaxed = false;
for (MCSection &Sec : *this) {
while (layoutSectionOnce(Layout, Sec))
WasRelaxed = true;
}
return WasRelaxed;
}
void MCAssembler::finishLayout(MCAsmLayout &Layout) {
assert(getBackendPtr() && "Expected assembler backend");
// The layout is done. Mark every fragment as valid.
for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
MCSection &Section = *Layout.getSectionOrder()[i];
Layout.getFragmentOffset(&*Section.getFragmentList().rbegin());
computeFragmentSize(Layout, *Section.getFragmentList().rbegin());
}
getBackend().finishLayout(*this, Layout);
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void MCAssembler::dump() const{
raw_ostream &OS = errs();
OS << "<MCAssembler\n";
OS << " Sections:[\n ";
for (const_iterator it = begin(), ie = end(); it != ie; ++it) {
if (it != begin()) OS << ",\n ";
it->dump();
}
OS << "],\n";
OS << " Symbols:[";
for (const_symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
if (it != symbol_begin()) OS << ",\n ";
OS << "(";
it->dump();
OS << ", Index:" << it->getIndex() << ", ";
OS << ")";
}
OS << "]>\n";
}
#endif
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