[MC] Allow MCObjectWriter's output stream to be swapped out
There are occasions where it is useful to consider the entirety of the
contents of a section. For example, compressed debug info needs the
entire section available before it can compress it and write it out.
The compressed debug info scenario was previously implemented by
mirroring the implementation of writeSectionData in the ELFObjectWriter.
Instead, allow the output stream to be swapped on demand. This lets
callers redirect the output stream to a more convenient location before
it hits the object file.
No functionality change is intended.
Differential Revision: http://reviews.llvm.org/D12509
llvm-svn: 246554
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index e925bc2..16f299c 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -157,9 +157,9 @@
template <typename T> void write(T Val) {
if (IsLittleEndian)
- support::endian::Writer<support::little>(OS).write(Val);
+ support::endian::Writer<support::little>(getStream()).write(Val);
else
- support::endian::Writer<support::big>(OS).write(Val);
+ support::endian::Writer<support::big>(getStream()).write(Val);
}
void writeHeader(const MCAssembler &Asm);
@@ -232,7 +232,7 @@
}
void ELFObjectWriter::align(unsigned Alignment) {
- uint64_t Padding = OffsetToAlignment(OS.tell(), Alignment);
+ uint64_t Padding = OffsetToAlignment(getStream().tell(), Alignment);
WriteZeros(Padding);
}
@@ -764,7 +764,7 @@
SymbolTableIndex = addToSectionTable(SymtabSection);
align(SymtabSection->getAlignment());
- uint64_t SecStart = OS.tell();
+ uint64_t SecStart = getStream().tell();
// The first entry is the undefined symbol entry.
Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
@@ -911,7 +911,7 @@
assert(MSD.Symbol->getBinding() != ELF::STB_LOCAL);
}
- uint64_t SecEnd = OS.tell();
+ uint64_t SecEnd = getStream().tell();
SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
@@ -921,12 +921,12 @@
}
assert(SymtabShndxSectionIndex != 0);
- SecStart = OS.tell();
+ SecStart = getStream().tell();
const MCSectionELF *SymtabShndxSection =
SectionTable[SymtabShndxSectionIndex - 1];
for (uint32_t Index : ShndxIndexes)
write(Index);
- SecEnd = OS.tell();
+ SecEnd = getStream().tell();
SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
}
@@ -957,31 +957,6 @@
return RelaSection;
}
-static SmallVector<char, 128>
-getUncompressedData(const MCAsmLayout &Layout,
- const MCSection::FragmentListType &Fragments) {
- SmallVector<char, 128> UncompressedData;
- for (const MCFragment &F : Fragments) {
- const SmallVectorImpl<char> *Contents;
- switch (F.getKind()) {
- case MCFragment::FT_Data:
- Contents = &cast<MCDataFragment>(F).getContents();
- break;
- case MCFragment::FT_Dwarf:
- Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
- break;
- case MCFragment::FT_DwarfFrame:
- Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
- break;
- default:
- llvm_unreachable(
- "Not expecting any other fragment types in a debug_* section");
- }
- UncompressedData.append(Contents->begin(), Contents->end());
- }
- return UncompressedData;
-}
-
// Include the debug info compression header:
// "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
// useful for consumers to preallocate a buffer to decompress into.
@@ -1016,27 +991,29 @@
return;
}
- // Gather the uncompressed data from all the fragments.
- const MCSection::FragmentListType &Fragments = Section.getFragmentList();
- SmallVector<char, 128> UncompressedData =
- getUncompressedData(Layout, Fragments);
+ SmallVector<char, 128> UncompressedData;
+ raw_svector_ostream VecOS(UncompressedData);
+ raw_pwrite_stream &OldStream = getStream();
+ setStream(VecOS);
+ Asm.writeSectionData(&Section, Layout);
+ setStream(OldStream);
SmallVector<char, 128> CompressedContents;
zlib::Status Success = zlib::compress(
StringRef(UncompressedData.data(), UncompressedData.size()),
CompressedContents);
if (Success != zlib::StatusOK) {
- Asm.writeSectionData(&Section, Layout);
+ getStream() << UncompressedData;
return;
}
if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
- Asm.writeSectionData(&Section, Layout);
+ getStream() << UncompressedData;
return;
}
Asm.getContext().renameELFSection(&Section,
(".z" + SectionName.drop_front(1)).str());
- OS << CompressedContents;
+ getStream() << CompressedContents;
}
void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
@@ -1100,7 +1077,7 @@
const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
- OS << StrTabBuilder.data();
+ getStream() << StrTabBuilder.data();
return StrtabSection;
}
@@ -1209,12 +1186,12 @@
align(Section.getAlignment());
// Remember the offset into the file for this section.
- uint64_t SecStart = OS.tell();
+ uint64_t SecStart = getStream().tell();
const MCSymbolELF *SignatureSymbol = Section.getGroup();
writeSectionData(Asm, Section, Layout);
- uint64_t SecEnd = OS.tell();
+ uint64_t SecEnd = getStream().tell();
SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
@@ -1246,7 +1223,7 @@
align(Group->getAlignment());
// Remember the offset into the file for this section.
- uint64_t SecStart = OS.tell();
+ uint64_t SecStart = getStream().tell();
const MCSymbol *SignatureSymbol = Group->getGroup();
assert(SignatureSymbol);
@@ -1256,7 +1233,7 @@
write(SecIndex);
}
- uint64_t SecEnd = OS.tell();
+ uint64_t SecEnd = getStream().tell();
SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
}
@@ -1267,25 +1244,25 @@
align(RelSection->getAlignment());
// Remember the offset into the file for this section.
- uint64_t SecStart = OS.tell();
+ uint64_t SecStart = getStream().tell();
writeRelocations(Asm, *RelSection->getAssociatedSection());
- uint64_t SecEnd = OS.tell();
+ uint64_t SecEnd = getStream().tell();
SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
}
{
- uint64_t SecStart = OS.tell();
+ uint64_t SecStart = getStream().tell();
const MCSectionELF *Sec = createStringTable(Ctx);
- uint64_t SecEnd = OS.tell();
+ uint64_t SecEnd = getStream().tell();
SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
}
uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
align(NaturalAlignment);
- const unsigned SectionHeaderOffset = OS.tell();
+ const unsigned SectionHeaderOffset = getStream().tell();
// ... then the section header table ...
writeSectionHeader(Layout, SectionIndexMap, SectionOffsets);
@@ -1301,19 +1278,19 @@
uint64_t Val = SectionHeaderOffset;
if (sys::IsLittleEndianHost != IsLittleEndian)
sys::swapByteOrder(Val);
- OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
- offsetof(ELF::Elf64_Ehdr, e_shoff));
+ getStream().pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
+ offsetof(ELF::Elf64_Ehdr, e_shoff));
NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
} else {
uint32_t Val = SectionHeaderOffset;
if (sys::IsLittleEndianHost != IsLittleEndian)
sys::swapByteOrder(Val);
- OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
- offsetof(ELF::Elf32_Ehdr, e_shoff));
+ getStream().pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
+ offsetof(ELF::Elf32_Ehdr, e_shoff));
NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
}
- OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
- NumSectionsOffset);
+ getStream().pwrite(reinterpret_cast<char *>(&NumSections),
+ sizeof(NumSections), NumSectionsOffset);
}
bool ELFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(