[llvm] r236267 - Simplify the creation of compressed debug sections.
Rafael Espindola
rafael.espindola at gmail.com
Thu Apr 30 14:51:59 PDT 2015
Author: rafael
Date: Thu Apr 30 16:51:58 2015
New Revision: 236267
URL: http://llvm.org/viewvc/llvm-project?rev=236267&view=rev
Log:
Simplify the creation of compressed debug sections.
This is actually fairly simple in the current code layout: Check if we should
compress just before writing out and everything else just works.
This removes the last case in which the object writer was creating a
fragment.
Modified:
llvm/trunk/lib/MC/ELFObjectWriter.cpp
Modified: llvm/trunk/lib/MC/ELFObjectWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/ELFObjectWriter.cpp?rev=236267&r1=236266&r2=236267&view=diff
==============================================================================
--- llvm/trunk/lib/MC/ELFObjectWriter.cpp (original)
+++ llvm/trunk/lib/MC/ELFObjectWriter.cpp Thu Apr 30 16:51:58 2015
@@ -182,8 +182,6 @@ class ELFObjectWriter : public MCObjectW
support::endian::Writer<support::big>(OS).write(Val);
}
- template <typename T> void write(MCDataFragment &F, T Value);
-
void writeHeader(const MCAssembler &Asm);
void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
@@ -224,8 +222,6 @@ class ELFObjectWriter : public MCObjectW
const MCSectionELF *createRelocationSection(MCAssembler &Asm,
const MCSectionELF &Sec);
- void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
-
const MCSectionELF *createSectionHeaderStringTable();
const MCSectionELF *createStringTable(MCContext &Ctx);
@@ -236,10 +232,13 @@ class ELFObjectWriter : public MCObjectW
const SectionIndexMapTy &SectionIndexMap,
const SectionOffsetsTy &SectionOffsets);
+ void writeSectionData(const MCAssembler &Asm, const MCSectionData &SD,
+ const MCAsmLayout &Layout);
+
void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
- uint64_t Address, uint64_t Offset,
- uint64_t Size, uint32_t Link, uint32_t Info,
- uint64_t Alignment, uint64_t EntrySize);
+ uint64_t Address, uint64_t Offset, uint64_t Size,
+ uint32_t Link, uint32_t Info, uint64_t Alignment,
+ uint64_t EntrySize);
void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
@@ -267,15 +266,6 @@ unsigned ELFObjectWriter::addToSectionTa
return SectionTable.size();
}
-template <typename T> void ELFObjectWriter::write(MCDataFragment &F, T Val) {
- if (IsLittleEndian)
- Val = support::endian::byte_swap<T, support::little>(Val);
- else
- Val = support::endian::byte_swap<T, support::big>(Val);
- const char *Start = (const char *)&Val;
- F.getContents().append(Start, Start + sizeof(T));
-}
-
void SymbolTableWriter::createSymtabShndx() {
if (!ShndxIndexes.empty())
return;
@@ -1105,7 +1095,7 @@ ELFObjectWriter::createRelocationSection
static SmallVector<char, 128>
getUncompressedData(const MCAsmLayout &Layout,
- MCSectionData::FragmentListType &Fragments) {
+ const MCSectionData::FragmentListType &Fragments) {
SmallVector<char, 128> UncompressedData;
for (const MCFragment &F : Fragments) {
const SmallVectorImpl<char> *Contents;
@@ -1148,104 +1138,43 @@ prependCompressionHeader(uint64_t Size,
return true;
}
-// Return a single fragment containing the compressed contents of the whole
-// section. Null if the section was not compressed for any reason.
-static std::unique_ptr<MCDataFragment>
-getCompressedFragment(const MCAsmLayout &Layout,
- MCSectionData::FragmentListType &Fragments) {
- std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
+void ELFObjectWriter::writeSectionData(const MCAssembler &Asm,
+ const MCSectionData &SD,
+ const MCAsmLayout &Layout) {
+ const MCSectionELF &Section =
+ static_cast<const MCSectionELF &>(SD.getSection());
+ StringRef SectionName = Section.getSectionName();
+
+ // Compressing debug_frame requires handling alignment fragments which is
+ // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
+ // for writing to arbitrary buffers) for little benefit.
+ if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
+ !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
+ Asm.writeSectionData(&SD, Layout);
+ return;
+ }
- // Gather the uncompressed data from all the fragments, recording the
- // alignment fragment, if seen, and any fixups.
+ // Gather the uncompressed data from all the fragments.
+ const MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
SmallVector<char, 128> UncompressedData =
getUncompressedData(Layout, Fragments);
- SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
-
+ SmallVector<char, 128> CompressedContents;
zlib::Status Success = zlib::compress(
StringRef(UncompressedData.data(), UncompressedData.size()),
CompressedContents);
- if (Success != zlib::StatusOK)
- return nullptr;
-
- if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
- return nullptr;
-
- return CompressedFragment;
-}
-
-typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
-DefiningSymbolMap;
-
-static void UpdateSymbols(const MCAsmLayout &Layout,
- const std::vector<MCSymbolData *> &Symbols,
- MCFragment &NewFragment) {
- for (MCSymbolData *Sym : Symbols) {
- Sym->setOffset(Sym->getOffset() +
- Layout.getFragmentOffset(Sym->getFragment()));
- Sym->setFragment(&NewFragment);
+ if (Success != zlib::StatusOK) {
+ Asm.writeSectionData(&SD, Layout);
+ return;
}
-}
-static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
- const DefiningSymbolMap &DefiningSymbols,
- const MCSectionELF &Section,
- MCSectionData &SD) {
- StringRef SectionName = Section.getSectionName();
- MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
-
- std::unique_ptr<MCDataFragment> CompressedFragment =
- getCompressedFragment(Layout, Fragments);
-
- // Leave the section as-is if the fragments could not be compressed.
- if (!CompressedFragment)
+ if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
+ Asm.writeSectionData(&SD, Layout);
return;
-
- // Update the fragment+offsets of any symbols referring to fragments in this
- // section to refer to the new fragment.
- auto I = DefiningSymbols.find(&SD);
- if (I != DefiningSymbols.end())
- UpdateSymbols(Layout, I->second, *CompressedFragment);
-
- // Invalidate the layout for the whole section since it will have new and
- // different fragments now.
- Layout.invalidateFragmentsFrom(&Fragments.front());
- Fragments.clear();
-
- // Complete the initialization of the new fragment
- CompressedFragment->setParent(&SD);
- CompressedFragment->setLayoutOrder(0);
- Fragments.push_back(CompressedFragment.release());
-
- // Rename from .debug_* to .zdebug_*
+ }
Asm.getContext().renameELFSection(&Section,
(".z" + SectionName.drop_front(1)).str());
-}
-
-void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
- MCAsmLayout &Layout) {
- if (!Asm.getContext().getAsmInfo()->compressDebugSections())
- return;
-
- DefiningSymbolMap DefiningSymbols;
-
- for (MCSymbolData &SD : Asm.symbols())
- if (MCFragment *F = SD.getFragment())
- DefiningSymbols[F->getParent()].push_back(&SD);
-
- for (MCSectionData &SD : Asm) {
- const MCSectionELF &Section =
- static_cast<const MCSectionELF &>(SD.getSection());
- StringRef SectionName = Section.getSectionName();
-
- // Compressing debug_frame requires handling alignment fragments which is
- // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
- // for writing to arbitrary buffers) for little benefit.
- if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
- continue;
-
- CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
- }
+ OS << CompressedContents;
}
void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
@@ -1408,8 +1337,6 @@ void ELFObjectWriter::writeSectionHeader
void ELFObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
- CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
-
MCContext &Ctx = Asm.getContext();
const MCSectionELF *ShstrtabSection =
Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
@@ -1453,7 +1380,7 @@ void ELFObjectWriter::WriteObject(MCAsse
}
writeRelocations(Asm, *Section.getAssociatedSection());
} else {
- Asm.writeSectionData(&SD, Layout);
+ writeSectionData(Asm, SD, Layout);
}
uint64_t SecEnd = OS.tell();
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