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llvm-mirror/lib/MC/MCAssembler.cpp
Saleem Abdulrasool f56e4f6d3d RISCV: adjust handling of relocation emission for RISCV 
This re-architects the RISCV relocation handling to bring the
implementation closer in line with the implementation in binutils.  We
would previously aggressively resolve the relocation.  With this
restructuring, we always will emit a paired relocation for any symbolic
difference of the type of S±T[±C] where S and T are labels and C is a
constant.

GAS has a special target hook controlled by `RELOC_EXPANSION_POSSIBLE`
which indicates that a fixup may be expanded into multiple relocations.
This is used by the RISCV backend to always emit a paired relocation -
either ADD[WIDTH] + SUB[WIDTH] for text relocations or SET[WIDTH] +
SUB[WIDTH] for a debug info relocation.  Irrespective of whether linker
relaxation support is enabled, symbolic difference is always emitted as
a paired relocation.

This change also sinks the target specific behaviour down into the
target specific area rather than exposing it to the shared relocation
handling.  In the process, we also sink the "special" handling for debug
information down into the RISCV target.  Although this improves the path
for the other targets, this is not necessarily entirely ideal either.
The changes in the debug info emission could be done through another
type of hook as this functionality would be required by any other target
which wishes to do linker relaxation.  However, as there are no other
targets in LLVM which currently do this, this is a reasonable thing to
do until such time as the code needs to be shared.

Improve the handling of the relocation (and add a reduced test case from
the Linux kernel) to ensure that we handle complex expressions for
symbolic difference.  This ensures that we correct relocate symbols with
the adddends normalized and associated with the addition portion of the
paired relocation.

This change also addresses some review comments from Alex Bradbury about
the relocations meant for use in the DWARF CFA being named incorrectly
(using ADD6 instead of SET6) in the original change which introduced the
relocation type.

This resolves the issues with the symbolic difference emission
sufficiently to enable building the Linux kernel with clang+IAS+lld
(without linker relaxation).

Resolves PR50153, PR50156!
Fixes: ClangBuiltLinux/linux#1023, ClangBuiltLinux/linux#1143

Reviewed By: nickdesaulniers, maskray

Differential Revision: https://reviews.llvm.org/D103539
2021-06-17 08:20:02 -07:00

1252 lines
44 KiB
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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(EmittedNopsFragments, "Number of emitted assembler fragments - nops");
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_Nops:
return cast<MCNopsFragment>(F).getNumBytes();
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_PseudoProbe:
return cast<MCPseudoProbeAddrFragment>(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_Nops: {
++stats::EmittedNopsFragments;
const MCNopsFragment &NF = cast<MCNopsFragment>(F);
int64_t NumBytes = NF.getNumBytes();
int64_t ControlledNopLength = NF.getControlledNopLength();
int64_t MaximumNopLength = Asm.getBackend().getMaximumNopSize();
assert(NumBytes > 0 && "Expected positive NOPs fragment size");
assert(ControlledNopLength >= 0 && "Expected non-negative NOP size");
if (ControlledNopLength > MaximumNopLength) {
Asm.getContext().reportError(NF.getLoc(),
"illegal NOP size " +
std::to_string(ControlledNopLength) +
". (expected within [0, " +
std::to_string(MaximumNopLength) + "])");
// Clamp the NOP length as reportError does not stop the execution
// immediately.
ControlledNopLength = MaximumNopLength;
}
// Use maximum value if the size of each NOP is not specified
if (!ControlledNopLength)
ControlledNopLength = MaximumNopLength;
while (NumBytes) {
uint64_t NumBytesToEmit =
(uint64_t)std::min(NumBytes, ControlledNopLength);
assert(NumBytesToEmit && "try to emit empty NOP instruction");
if (!Asm.getBackend().writeNopData(OS, NumBytesToEmit)) {
report_fatal_error("unable to write nop sequence of the remaining " +
Twine(NumBytesToEmit) + " bytes");
break;
}
NumBytes -= NumBytesToEmit;
}
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_PseudoProbe: {
const MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(F);
OS << PF.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;
case MCFragment::FT_Org:
break;
}
}
return;
}
uint64_t Start = OS.tell();
(void)Start;
for (const MCFragment &F : *Sec)
writeFragment(OS, *this, Layout, F);
assert(getContext().hadError() ||
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.
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;
}
case MCFragment::FT_PseudoProbe: {
MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(Frag);
Fixups = PF.getFixups();
Contents = PF.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) {
bool WasRelaxed;
if (getBackend().relaxDwarfLineAddr(DF, Layout, WasRelaxed))
return WasRelaxed;
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();
MCDwarfLineAddr::Encode(Context, getDWARFLinetableParams(), LineDelta,
AddrDelta, OSE);
return OldSize != Data.size();
}
bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
MCDwarfCallFrameFragment &DF) {
bool WasRelaxed;
if (getBackend().relaxDwarfCFA(DF, Layout, WasRelaxed))
return WasRelaxed;
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();
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::relaxPseudoProbeAddr(MCAsmLayout &Layout,
MCPseudoProbeAddrFragment &PF) {
uint64_t OldSize = PF.getContents().size();
int64_t AddrDelta;
bool Abs = PF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
assert(Abs && "We created a pseudo probe with an invalid expression");
(void)Abs;
SmallVectorImpl<char> &Data = PF.getContents();
Data.clear();
raw_svector_ostream OSE(Data);
PF.getFixups().clear();
// AddrDelta is a signed integer
encodeSLEB128(AddrDelta, OSE, OldSize);
return OldSize != Data.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));
case MCFragment::FT_PseudoProbe:
return relaxPseudoProbeAddr(Layout, cast<MCPseudoProbeAddrFragment>(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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