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llvm-mirror/lib/MC/MCCodeView.cpp
Chandler Carruth ae65e281f3 Update the file headers across all of the LLVM projects in the monorepo 
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636
2019-01-19 08:50:56 +00:00

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26 KiB
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//===- MCCodeView.h - Machine Code CodeView support -------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Holds state from .cv_file and .cv_loc directives for later emission.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCCodeView.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/DebugInfo/CodeView/CodeView.h"
#include "llvm/DebugInfo/CodeView/Line.h"
#include "llvm/DebugInfo/CodeView/SymbolRecord.h"
#include "llvm/MC/MCAsmLayout.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/EndianStream.h"
using namespace llvm;
using namespace llvm::codeview;
CodeViewContext::CodeViewContext() {}
CodeViewContext::~CodeViewContext() {
// If someone inserted strings into the string table but never actually
// emitted them somewhere, clean up the fragment.
if (!InsertedStrTabFragment)
delete StrTabFragment;
}
/// This is a valid number for use with .cv_loc if we've already seen a .cv_file
/// for it.
bool CodeViewContext::isValidFileNumber(unsigned FileNumber) const {
unsigned Idx = FileNumber - 1;
if (Idx < Files.size())
return Files[Idx].Assigned;
return false;
}
bool CodeViewContext::addFile(MCStreamer &OS, unsigned FileNumber,
StringRef Filename,
ArrayRef<uint8_t> ChecksumBytes,
uint8_t ChecksumKind) {
assert(FileNumber > 0);
auto FilenameOffset = addToStringTable(Filename);
Filename = FilenameOffset.first;
unsigned Idx = FileNumber - 1;
if (Idx >= Files.size())
Files.resize(Idx + 1);
if (Filename.empty())
Filename = "<stdin>";
if (Files[Idx].Assigned)
return false;
FilenameOffset = addToStringTable(Filename);
Filename = FilenameOffset.first;
unsigned Offset = FilenameOffset.second;
auto ChecksumOffsetSymbol =
OS.getContext().createTempSymbol("checksum_offset", false);
Files[Idx].StringTableOffset = Offset;
Files[Idx].ChecksumTableOffset = ChecksumOffsetSymbol;
Files[Idx].Assigned = true;
Files[Idx].Checksum = ChecksumBytes;
Files[Idx].ChecksumKind = ChecksumKind;
return true;
}
MCCVFunctionInfo *CodeViewContext::getCVFunctionInfo(unsigned FuncId) {
if (FuncId >= Functions.size())
return nullptr;
if (Functions[FuncId].isUnallocatedFunctionInfo())
return nullptr;
return &Functions[FuncId];
}
bool CodeViewContext::recordFunctionId(unsigned FuncId) {
if (FuncId >= Functions.size())
Functions.resize(FuncId + 1);
// Return false if this function info was already allocated.
if (!Functions[FuncId].isUnallocatedFunctionInfo())
return false;
// Mark this as an allocated normal function, and leave the rest alone.
Functions[FuncId].ParentFuncIdPlusOne = MCCVFunctionInfo::FunctionSentinel;
return true;
}
bool CodeViewContext::recordInlinedCallSiteId(unsigned FuncId, unsigned IAFunc,
unsigned IAFile, unsigned IALine,
unsigned IACol) {
if (FuncId >= Functions.size())
Functions.resize(FuncId + 1);
// Return false if this function info was already allocated.
if (!Functions[FuncId].isUnallocatedFunctionInfo())
return false;
MCCVFunctionInfo::LineInfo InlinedAt;
InlinedAt.File = IAFile;
InlinedAt.Line = IALine;
InlinedAt.Col = IACol;
// Mark this as an inlined call site and record call site line info.
MCCVFunctionInfo *Info = &Functions[FuncId];
Info->ParentFuncIdPlusOne = IAFunc + 1;
Info->InlinedAt = InlinedAt;
// Walk up the call chain adding this function id to the InlinedAtMap of all
// transitive callers until we hit a real function.
while (Info->isInlinedCallSite()) {
InlinedAt = Info->InlinedAt;
Info = getCVFunctionInfo(Info->getParentFuncId());
Info->InlinedAtMap[FuncId] = InlinedAt;
}
return true;
}
void CodeViewContext::recordCVLoc(MCContext &Ctx, const MCSymbol *Label,
unsigned FunctionId, unsigned FileNo,
unsigned Line, unsigned Column,
bool PrologueEnd, bool IsStmt) {
addLineEntry(MCCVLoc{
Label, FunctionId, FileNo, Line, Column, PrologueEnd, IsStmt});
}
MCDataFragment *CodeViewContext::getStringTableFragment() {
if (!StrTabFragment) {
StrTabFragment = new MCDataFragment();
// Start a new string table out with a null byte.
StrTabFragment->getContents().push_back('\0');
}
return StrTabFragment;
}
std::pair<StringRef, unsigned> CodeViewContext::addToStringTable(StringRef S) {
SmallVectorImpl<char> &Contents = getStringTableFragment()->getContents();
auto Insertion =
StringTable.insert(std::make_pair(S, unsigned(Contents.size())));
// Return the string from the table, since it is stable.
std::pair<StringRef, unsigned> Ret =
std::make_pair(Insertion.first->first(), Insertion.first->second);
if (Insertion.second) {
// The string map key is always null terminated.
Contents.append(Ret.first.begin(), Ret.first.end() + 1);
}
return Ret;
}
unsigned CodeViewContext::getStringTableOffset(StringRef S) {
// A string table offset of zero is always the empty string.
if (S.empty())
return 0;
auto I = StringTable.find(S);
assert(I != StringTable.end());
return I->second;
}
void CodeViewContext::emitStringTable(MCObjectStreamer &OS) {
MCContext &Ctx = OS.getContext();
MCSymbol *StringBegin = Ctx.createTempSymbol("strtab_begin", false),
*StringEnd = Ctx.createTempSymbol("strtab_end", false);
OS.EmitIntValue(unsigned(DebugSubsectionKind::StringTable), 4);
OS.emitAbsoluteSymbolDiff(StringEnd, StringBegin, 4);
OS.EmitLabel(StringBegin);
// Put the string table data fragment here, if we haven't already put it
// somewhere else. If somebody wants two string tables in their .s file, one
// will just be empty.
if (!InsertedStrTabFragment) {
OS.insert(getStringTableFragment());
InsertedStrTabFragment = true;
}
OS.EmitValueToAlignment(4, 0);
OS.EmitLabel(StringEnd);
}
void CodeViewContext::emitFileChecksums(MCObjectStreamer &OS) {
// Do nothing if there are no file checksums. Microsoft's linker rejects empty
// CodeView substreams.
if (Files.empty())
return;
MCContext &Ctx = OS.getContext();
MCSymbol *FileBegin = Ctx.createTempSymbol("filechecksums_begin", false),
*FileEnd = Ctx.createTempSymbol("filechecksums_end", false);
OS.EmitIntValue(unsigned(DebugSubsectionKind::FileChecksums), 4);
OS.emitAbsoluteSymbolDiff(FileEnd, FileBegin, 4);
OS.EmitLabel(FileBegin);
unsigned CurrentOffset = 0;
// Emit an array of FileChecksum entries. We index into this table using the
// user-provided file number. Each entry may be a variable number of bytes
// determined by the checksum kind and size.
for (auto File : Files) {
OS.EmitAssignment(File.ChecksumTableOffset,
MCConstantExpr::create(CurrentOffset, Ctx));
CurrentOffset += 4; // String table offset.
if (!File.ChecksumKind) {
CurrentOffset +=
4; // One byte each for checksum size and kind, then align to 4 bytes.
} else {
CurrentOffset += 2; // One byte each for checksum size and kind.
CurrentOffset += File.Checksum.size();
CurrentOffset = alignTo(CurrentOffset, 4);
}
OS.EmitIntValue(File.StringTableOffset, 4);
if (!File.ChecksumKind) {
// There is no checksum. Therefore zero the next two fields and align
// back to 4 bytes.
OS.EmitIntValue(0, 4);
continue;
}
OS.EmitIntValue(static_cast<uint8_t>(File.Checksum.size()), 1);
OS.EmitIntValue(File.ChecksumKind, 1);
OS.EmitBytes(toStringRef(File.Checksum));
OS.EmitValueToAlignment(4);
}
OS.EmitLabel(FileEnd);
ChecksumOffsetsAssigned = true;
}
// Output checksum table offset of the given file number. It is possible that
// not all files have been registered yet, and so the offset cannot be
// calculated. In this case a symbol representing the offset is emitted, and
// the value of this symbol will be fixed up at a later time.
void CodeViewContext::emitFileChecksumOffset(MCObjectStreamer &OS,
unsigned FileNo) {
unsigned Idx = FileNo - 1;
if (Idx >= Files.size())
Files.resize(Idx + 1);
if (ChecksumOffsetsAssigned) {
OS.EmitSymbolValue(Files[Idx].ChecksumTableOffset, 4);
return;
}
const MCSymbolRefExpr *SRE =
MCSymbolRefExpr::create(Files[Idx].ChecksumTableOffset, OS.getContext());
OS.EmitValueImpl(SRE, 4);
}
void CodeViewContext::addLineEntry(const MCCVLoc &LineEntry) {
size_t Offset = MCCVLines.size();
auto I = MCCVLineStartStop.insert(
{LineEntry.getFunctionId(), {Offset, Offset + 1}});
if (!I.second)
I.first->second.second = Offset + 1;
MCCVLines.push_back(LineEntry);
}
std::vector<MCCVLoc>
CodeViewContext::getFunctionLineEntries(unsigned FuncId) {
std::vector<MCCVLoc> FilteredLines;
auto I = MCCVLineStartStop.find(FuncId);
if (I != MCCVLineStartStop.end()) {
MCCVFunctionInfo *SiteInfo = getCVFunctionInfo(FuncId);
for (size_t Idx = I->second.first, End = I->second.second; Idx != End;
++Idx) {
unsigned LocationFuncId = MCCVLines[Idx].getFunctionId();
if (LocationFuncId == FuncId) {
// This was a .cv_loc directly for FuncId, so record it.
FilteredLines.push_back(MCCVLines[Idx]);
} else {
// Check if the current location is inlined in this function. If it is,
// synthesize a statement .cv_loc at the original inlined call site.
auto I = SiteInfo->InlinedAtMap.find(LocationFuncId);
if (I != SiteInfo->InlinedAtMap.end()) {
MCCVFunctionInfo::LineInfo &IA = I->second;
// Only add the location if it differs from the previous location.
// Large inlined calls will have many .cv_loc entries and we only need
// one line table entry in the parent function.
if (FilteredLines.empty() ||
FilteredLines.back().getFileNum() != IA.File ||
FilteredLines.back().getLine() != IA.Line ||
FilteredLines.back().getColumn() != IA.Col) {
FilteredLines.push_back(MCCVLoc(
MCCVLines[Idx].getLabel(),
FuncId, IA.File, IA.Line, IA.Col, false, false));
}
}
}
}
}
return FilteredLines;
}
std::pair<size_t, size_t> CodeViewContext::getLineExtent(unsigned FuncId) {
auto I = MCCVLineStartStop.find(FuncId);
// Return an empty extent if there are no cv_locs for this function id.
if (I == MCCVLineStartStop.end())
return {~0ULL, 0};
return I->second;
}
ArrayRef<MCCVLoc> CodeViewContext::getLinesForExtent(size_t L, size_t R) {
if (R <= L)
return None;
if (L >= MCCVLines.size())
return None;
return makeArrayRef(&MCCVLines[L], R - L);
}
void CodeViewContext::emitLineTableForFunction(MCObjectStreamer &OS,
unsigned FuncId,
const MCSymbol *FuncBegin,
const MCSymbol *FuncEnd) {
MCContext &Ctx = OS.getContext();
MCSymbol *LineBegin = Ctx.createTempSymbol("linetable_begin", false),
*LineEnd = Ctx.createTempSymbol("linetable_end", false);
OS.EmitIntValue(unsigned(DebugSubsectionKind::Lines), 4);
OS.emitAbsoluteSymbolDiff(LineEnd, LineBegin, 4);
OS.EmitLabel(LineBegin);
OS.EmitCOFFSecRel32(FuncBegin, /*Offset=*/0);
OS.EmitCOFFSectionIndex(FuncBegin);
// Actual line info.
std::vector<MCCVLoc> Locs = getFunctionLineEntries(FuncId);
bool HaveColumns = any_of(Locs, [](const MCCVLoc &LineEntry) {
return LineEntry.getColumn() != 0;
});
OS.EmitIntValue(HaveColumns ? int(LF_HaveColumns) : 0, 2);
OS.emitAbsoluteSymbolDiff(FuncEnd, FuncBegin, 4);
for (auto I = Locs.begin(), E = Locs.end(); I != E;) {
// Emit a file segment for the run of locations that share a file id.
unsigned CurFileNum = I->getFileNum();
auto FileSegEnd =
std::find_if(I, E, [CurFileNum](const MCCVLoc &Loc) {
return Loc.getFileNum() != CurFileNum;
});
unsigned EntryCount = FileSegEnd - I;
OS.AddComment(
"Segment for file '" +
Twine(getStringTableFragment()
->getContents()[Files[CurFileNum - 1].StringTableOffset]) +
"' begins");
OS.EmitCVFileChecksumOffsetDirective(CurFileNum);
OS.EmitIntValue(EntryCount, 4);
uint32_t SegmentSize = 12;
SegmentSize += 8 * EntryCount;
if (HaveColumns)
SegmentSize += 4 * EntryCount;
OS.EmitIntValue(SegmentSize, 4);
for (auto J = I; J != FileSegEnd; ++J) {
OS.emitAbsoluteSymbolDiff(J->getLabel(), FuncBegin, 4);
unsigned LineData = J->getLine();
if (J->isStmt())
LineData |= LineInfo::StatementFlag;
OS.EmitIntValue(LineData, 4);
}
if (HaveColumns) {
for (auto J = I; J != FileSegEnd; ++J) {
OS.EmitIntValue(J->getColumn(), 2);
OS.EmitIntValue(0, 2);
}
}
I = FileSegEnd;
}
OS.EmitLabel(LineEnd);
}
static bool compressAnnotation(uint32_t Data, SmallVectorImpl<char> &Buffer) {
if (isUInt<7>(Data)) {
Buffer.push_back(Data);
return true;
}
if (isUInt<14>(Data)) {
Buffer.push_back((Data >> 8) | 0x80);
Buffer.push_back(Data & 0xff);
return true;
}
if (isUInt<29>(Data)) {
Buffer.push_back((Data >> 24) | 0xC0);
Buffer.push_back((Data >> 16) & 0xff);
Buffer.push_back((Data >> 8) & 0xff);
Buffer.push_back(Data & 0xff);
return true;
}
return false;
}
static bool compressAnnotation(BinaryAnnotationsOpCode Annotation,
SmallVectorImpl<char> &Buffer) {
return compressAnnotation(static_cast<uint32_t>(Annotation), Buffer);
}
static uint32_t encodeSignedNumber(uint32_t Data) {
if (Data >> 31)
return ((-Data) << 1) | 1;
return Data << 1;
}
void CodeViewContext::emitInlineLineTableForFunction(MCObjectStreamer &OS,
unsigned PrimaryFunctionId,
unsigned SourceFileId,
unsigned SourceLineNum,
const MCSymbol *FnStartSym,
const MCSymbol *FnEndSym) {
// Create and insert a fragment into the current section that will be encoded
// later.
new MCCVInlineLineTableFragment(PrimaryFunctionId, SourceFileId,
SourceLineNum, FnStartSym, FnEndSym,
OS.getCurrentSectionOnly());
}
MCFragment *CodeViewContext::emitDefRange(
MCObjectStreamer &OS,
ArrayRef<std::pair<const MCSymbol *, const MCSymbol *>> Ranges,
StringRef FixedSizePortion) {
// Create and insert a fragment into the current section that will be encoded
// later.
return new MCCVDefRangeFragment(Ranges, FixedSizePortion,
OS.getCurrentSectionOnly());
}
static unsigned computeLabelDiff(MCAsmLayout &Layout, const MCSymbol *Begin,
const MCSymbol *End) {
MCContext &Ctx = Layout.getAssembler().getContext();
MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
const MCExpr *BeginRef = MCSymbolRefExpr::create(Begin, Variant, Ctx),
*EndRef = MCSymbolRefExpr::create(End, Variant, Ctx);
const MCExpr *AddrDelta =
MCBinaryExpr::create(MCBinaryExpr::Sub, EndRef, BeginRef, Ctx);
int64_t Result;
bool Success = AddrDelta->evaluateKnownAbsolute(Result, Layout);
assert(Success && "failed to evaluate label difference as absolute");
(void)Success;
assert(Result >= 0 && "negative label difference requested");
assert(Result < UINT_MAX && "label difference greater than 2GB");
return unsigned(Result);
}
void CodeViewContext::encodeInlineLineTable(MCAsmLayout &Layout,
MCCVInlineLineTableFragment &Frag) {
size_t LocBegin;
size_t LocEnd;
std::tie(LocBegin, LocEnd) = getLineExtent(Frag.SiteFuncId);
// Include all child inline call sites in our .cv_loc extent.
MCCVFunctionInfo *SiteInfo = getCVFunctionInfo(Frag.SiteFuncId);
for (auto &KV : SiteInfo->InlinedAtMap) {
unsigned ChildId = KV.first;
auto Extent = getLineExtent(ChildId);
LocBegin = std::min(LocBegin, Extent.first);
LocEnd = std::max(LocEnd, Extent.second);
}
if (LocBegin >= LocEnd)
return;
ArrayRef<MCCVLoc> Locs = getLinesForExtent(LocBegin, LocEnd);
if (Locs.empty())
return;
// Check that the locations are all in the same section.
#ifndef NDEBUG
const MCSection *FirstSec = &Locs.front().getLabel()->getSection();
for (const MCCVLoc &Loc : Locs) {
if (&Loc.getLabel()->getSection() != FirstSec) {
errs() << ".cv_loc " << Loc.getFunctionId() << ' ' << Loc.getFileNum()
<< ' ' << Loc.getLine() << ' ' << Loc.getColumn()
<< " is in the wrong section\n";
llvm_unreachable(".cv_loc crosses sections");
}
}
#endif
// Make an artificial start location using the function start and the inlinee
// lines start location information. All deltas start relative to this
// location.
MCCVLoc StartLoc = Locs.front();
StartLoc.setLabel(Frag.getFnStartSym());
StartLoc.setFileNum(Frag.StartFileId);
StartLoc.setLine(Frag.StartLineNum);
bool HaveOpenRange = false;
const MCSymbol *LastLabel = Frag.getFnStartSym();
MCCVFunctionInfo::LineInfo LastSourceLoc, CurSourceLoc;
LastSourceLoc.File = Frag.StartFileId;
LastSourceLoc.Line = Frag.StartLineNum;
SmallVectorImpl<char> &Buffer = Frag.getContents();
Buffer.clear(); // Clear old contents if we went through relaxation.
for (const MCCVLoc &Loc : Locs) {
// Exit early if our line table would produce an oversized InlineSiteSym
// record. Account for the ChangeCodeLength annotation emitted after the
// loop ends.
constexpr uint32_t InlineSiteSize = 12;
constexpr uint32_t AnnotationSize = 8;
size_t MaxBufferSize = MaxRecordLength - InlineSiteSize - AnnotationSize;
if (Buffer.size() >= MaxBufferSize)
break;
if (Loc.getFunctionId() == Frag.SiteFuncId) {
CurSourceLoc.File = Loc.getFileNum();
CurSourceLoc.Line = Loc.getLine();
} else {
auto I = SiteInfo->InlinedAtMap.find(Loc.getFunctionId());
if (I != SiteInfo->InlinedAtMap.end()) {
// This .cv_loc is from a child inline call site. Use the source
// location of the inlined call site instead of the .cv_loc directive
// source location.
CurSourceLoc = I->second;
} else {
// We've hit a cv_loc not attributed to this inline call site. Use this
// label to end the PC range.
if (HaveOpenRange) {
unsigned Length = computeLabelDiff(Layout, LastLabel, Loc.getLabel());
compressAnnotation(BinaryAnnotationsOpCode::ChangeCodeLength, Buffer);
compressAnnotation(Length, Buffer);
LastLabel = Loc.getLabel();
}
HaveOpenRange = false;
continue;
}
}
// Skip this .cv_loc if we have an open range and this isn't a meaningful
// source location update. The current table format does not support column
// info, so we can skip updates for those.
if (HaveOpenRange && CurSourceLoc.File == LastSourceLoc.File &&
CurSourceLoc.Line == LastSourceLoc.Line)
continue;
HaveOpenRange = true;
if (CurSourceLoc.File != LastSourceLoc.File) {
unsigned FileOffset = static_cast<const MCConstantExpr *>(
Files[CurSourceLoc.File - 1]
.ChecksumTableOffset->getVariableValue())
->getValue();
compressAnnotation(BinaryAnnotationsOpCode::ChangeFile, Buffer);
compressAnnotation(FileOffset, Buffer);
}
int LineDelta = CurSourceLoc.Line - LastSourceLoc.Line;
unsigned EncodedLineDelta = encodeSignedNumber(LineDelta);
unsigned CodeDelta = computeLabelDiff(Layout, LastLabel, Loc.getLabel());
if (CodeDelta == 0 && LineDelta != 0) {
compressAnnotation(BinaryAnnotationsOpCode::ChangeLineOffset, Buffer);
compressAnnotation(EncodedLineDelta, Buffer);
} else if (EncodedLineDelta < 0x8 && CodeDelta <= 0xf) {
// The ChangeCodeOffsetAndLineOffset combination opcode is used when the
// encoded line delta uses 3 or fewer set bits and the code offset fits
// in one nibble.
unsigned Operand = (EncodedLineDelta << 4) | CodeDelta;
compressAnnotation(BinaryAnnotationsOpCode::ChangeCodeOffsetAndLineOffset,
Buffer);
compressAnnotation(Operand, Buffer);
} else {
// Otherwise use the separate line and code deltas.
if (LineDelta != 0) {
compressAnnotation(BinaryAnnotationsOpCode::ChangeLineOffset, Buffer);
compressAnnotation(EncodedLineDelta, Buffer);
}
compressAnnotation(BinaryAnnotationsOpCode::ChangeCodeOffset, Buffer);
compressAnnotation(CodeDelta, Buffer);
}
LastLabel = Loc.getLabel();
LastSourceLoc = CurSourceLoc;
}
assert(HaveOpenRange);
unsigned EndSymLength =
computeLabelDiff(Layout, LastLabel, Frag.getFnEndSym());
unsigned LocAfterLength = ~0U;
ArrayRef<MCCVLoc> LocAfter = getLinesForExtent(LocEnd, LocEnd + 1);
if (!LocAfter.empty()) {
// Only try to compute this difference if we're in the same section.
const MCCVLoc &Loc = LocAfter[0];
if (&Loc.getLabel()->getSection() == &LastLabel->getSection())
LocAfterLength = computeLabelDiff(Layout, LastLabel, Loc.getLabel());
}
compressAnnotation(BinaryAnnotationsOpCode::ChangeCodeLength, Buffer);
compressAnnotation(std::min(EndSymLength, LocAfterLength), Buffer);
}
void CodeViewContext::encodeDefRange(MCAsmLayout &Layout,
MCCVDefRangeFragment &Frag) {
MCContext &Ctx = Layout.getAssembler().getContext();
SmallVectorImpl<char> &Contents = Frag.getContents();
Contents.clear();
SmallVectorImpl<MCFixup> &Fixups = Frag.getFixups();
Fixups.clear();
raw_svector_ostream OS(Contents);
// Compute all the sizes up front.
SmallVector<std::pair<unsigned, unsigned>, 4> GapAndRangeSizes;
const MCSymbol *LastLabel = nullptr;
for (std::pair<const MCSymbol *, const MCSymbol *> Range : Frag.getRanges()) {
unsigned GapSize =
LastLabel ? computeLabelDiff(Layout, LastLabel, Range.first) : 0;
unsigned RangeSize = computeLabelDiff(Layout, Range.first, Range.second);
GapAndRangeSizes.push_back({GapSize, RangeSize});
LastLabel = Range.second;
}
// Write down each range where the variable is defined.
for (size_t I = 0, E = Frag.getRanges().size(); I != E;) {
// If the range size of multiple consecutive ranges is under the max,
// combine the ranges and emit some gaps.
const MCSymbol *RangeBegin = Frag.getRanges()[I].first;
unsigned RangeSize = GapAndRangeSizes[I].second;
size_t J = I + 1;
for (; J != E; ++J) {
unsigned GapAndRangeSize = GapAndRangeSizes[J].first + GapAndRangeSizes[J].second;
if (RangeSize + GapAndRangeSize > MaxDefRange)
break;
RangeSize += GapAndRangeSize;
}
unsigned NumGaps = J - I - 1;
support::endian::Writer LEWriter(OS, support::little);
unsigned Bias = 0;
// We must split the range into chunks of MaxDefRange, this is a fundamental
// limitation of the file format.
do {
uint16_t Chunk = std::min((uint32_t)MaxDefRange, RangeSize);
const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(RangeBegin, Ctx);
const MCBinaryExpr *BE =
MCBinaryExpr::createAdd(SRE, MCConstantExpr::create(Bias, Ctx), Ctx);
MCValue Res;
BE->evaluateAsRelocatable(Res, &Layout, /*Fixup=*/nullptr);
// Each record begins with a 2-byte number indicating how large the record
// is.
StringRef FixedSizePortion = Frag.getFixedSizePortion();
// Our record is a fixed sized prefix and a LocalVariableAddrRange that we
// are artificially constructing.
size_t RecordSize = FixedSizePortion.size() +
sizeof(LocalVariableAddrRange) + 4 * NumGaps;
// Write out the record size.
LEWriter.write<uint16_t>(RecordSize);
// Write out the fixed size prefix.
OS << FixedSizePortion;
// Make space for a fixup that will eventually have a section relative
// relocation pointing at the offset where the variable becomes live.
Fixups.push_back(MCFixup::create(Contents.size(), BE, FK_SecRel_4));
LEWriter.write<uint32_t>(0); // Fixup for code start.
// Make space for a fixup that will record the section index for the code.
Fixups.push_back(MCFixup::create(Contents.size(), BE, FK_SecRel_2));
LEWriter.write<uint16_t>(0); // Fixup for section index.
// Write down the range's extent.
LEWriter.write<uint16_t>(Chunk);
// Move on to the next range.
Bias += Chunk;
RangeSize -= Chunk;
} while (RangeSize > 0);
// Emit the gaps afterwards.
assert((NumGaps == 0 || Bias <= MaxDefRange) &&
"large ranges should not have gaps");
unsigned GapStartOffset = GapAndRangeSizes[I].second;
for (++I; I != J; ++I) {
unsigned GapSize, RangeSize;
assert(I < GapAndRangeSizes.size());
std::tie(GapSize, RangeSize) = GapAndRangeSizes[I];
LEWriter.write<uint16_t>(GapStartOffset);
LEWriter.write<uint16_t>(GapSize);
GapStartOffset += GapSize + RangeSize;
}
}
}
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