MC: Introduce an ELF dwo object writer and teach llvm-mc about it.
Part of PR37466.
Differential Revision: https://reviews.llvm.org/D47051
llvm-svn: 332875
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index a8f88ce..1430064 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -70,6 +70,10 @@
class ELFObjectWriter;
struct ELFWriter;
+bool isDwoSection(const MCSectionELF &Sec) {
+ return Sec.getSectionName().endswith(".dwo");
+}
+
class SymbolTableWriter {
ELFWriter &EWriter;
bool Is64Bit;
@@ -97,6 +101,12 @@
ELFObjectWriter &OWriter;
support::endian::Writer W;
+ enum DwoMode {
+ AllSections,
+ NonDwoOnly,
+ DwoOnly,
+ } Mode;
+
static uint64_t SymbolValue(const MCSymbol &Sym, const MCAsmLayout &Layout);
static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
bool Used, bool Renamed);
@@ -152,9 +162,9 @@
public:
ELFWriter(ELFObjectWriter &OWriter, raw_pwrite_stream &OS,
- bool IsLittleEndian)
+ bool IsLittleEndian, DwoMode Mode)
: OWriter(OWriter),
- W(OS, IsLittleEndian ? support::little : support::big) {}
+ W(OS, IsLittleEndian ? support::little : support::big), Mode(Mode) {}
void WriteWord(uint64_t Word) {
if (is64Bit())
@@ -244,6 +254,12 @@
const MCFragment &FB, bool InSet,
bool IsPCRel) const override;
+ virtual bool checkRelocation(MCContext &Ctx, SMLoc Loc,
+ const MCSectionELF *From,
+ const MCSectionELF *To) {
+ return true;
+ }
+
void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, uint64_t &FixedValue) override;
@@ -265,7 +281,44 @@
IsLittleEndian(IsLittleEndian) {}
uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override {
- return ELFWriter(*this, OS, IsLittleEndian).writeObject(Asm, Layout);
+ return ELFWriter(*this, OS, IsLittleEndian, ELFWriter::AllSections)
+ .writeObject(Asm, Layout);
+ }
+
+ friend struct ELFWriter;
+};
+
+class ELFDwoObjectWriter : public ELFObjectWriter {
+ raw_pwrite_stream &OS, &DwoOS;
+ bool IsLittleEndian;
+
+public:
+ ELFDwoObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
+ raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS,
+ bool IsLittleEndian)
+ : ELFObjectWriter(std::move(MOTW)), OS(OS), DwoOS(DwoOS),
+ IsLittleEndian(IsLittleEndian) {}
+
+ virtual bool checkRelocation(MCContext &Ctx, SMLoc Loc,
+ const MCSectionELF *From,
+ const MCSectionELF *To) override {
+ if (isDwoSection(*From)) {
+ Ctx.reportError(Loc, "A dwo section may not contain relocations");
+ return false;
+ }
+ if (To && isDwoSection(*To)) {
+ Ctx.reportError(Loc, "A relocation may not refer to a dwo section");
+ return false;
+ }
+ return true;
+ }
+
+ uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override {
+ uint64_t Size = ELFWriter(*this, OS, IsLittleEndian, ELFWriter::NonDwoOnly)
+ .writeObject(Asm, Layout);
+ Size += ELFWriter(*this, DwoOS, IsLittleEndian, ELFWriter::DwoOnly)
+ .writeObject(Asm, Layout);
+ return Size;
}
};
@@ -604,6 +657,8 @@
} else {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(Symbol.getSection());
+ if (Mode == NonDwoOnly && isDwoSection(Section))
+ continue;
MSD.SectionIndex = SectionIndexMap.lookup(&Section);
assert(MSD.SectionIndex && "Invalid section index!");
if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
@@ -995,6 +1050,10 @@
std::vector<MCSectionELF *> Relocations;
for (MCSection &Sec : Asm) {
MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
+ if (Mode == NonDwoOnly && isDwoSection(Section))
+ continue;
+ if (Mode == DwoOnly && !isDwoSection(Section))
+ continue;
align(Section.getAlignment());
@@ -1050,20 +1109,27 @@
SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
}
- // Compute symbol table information.
- computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
+ if (Mode == DwoOnly) {
+ // dwo files don't have symbol tables or relocations, but they do have
+ // string tables.
+ StrTabBuilder.finalize();
+ } else {
+ // Compute symbol table information.
+ computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
+ SectionOffsets);
- for (MCSectionELF *RelSection : Relocations) {
- align(RelSection->getAlignment());
+ for (MCSectionELF *RelSection : Relocations) {
+ align(RelSection->getAlignment());
- // Remember the offset into the file for this section.
- uint64_t SecStart = W.OS.tell();
+ // Remember the offset into the file for this section.
+ uint64_t SecStart = W.OS.tell();
- writeRelocations(Asm,
- cast<MCSectionELF>(*RelSection->getAssociatedSection()));
+ writeRelocations(Asm,
+ cast<MCSectionELF>(*RelSection->getAssociatedSection()));
- uint64_t SecEnd = W.OS.tell();
- SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
+ uint64_t SecEnd = W.OS.tell();
+ SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
+ }
}
{
@@ -1336,9 +1402,13 @@
FixedValue = C;
+ const MCSectionELF *SecA = (SymA && SymA->isInSection())
+ ? cast<MCSectionELF>(&SymA->getSection())
+ : nullptr;
+ if (!checkRelocation(Ctx, Fixup.getLoc(), &FixupSection, SecA))
+ return;
+
if (!RelocateWithSymbol) {
- const MCSection *SecA =
- (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
const auto *SectionSymbol =
SecA ? cast<MCSymbolELF>(SecA->getBeginSymbol()) : nullptr;
if (SectionSymbol)
@@ -1383,3 +1453,11 @@
return llvm::make_unique<ELFSingleObjectWriter>(std::move(MOTW), OS,
IsLittleEndian);
}
+
+std::unique_ptr<MCObjectWriter>
+llvm::createELFDwoObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
+ raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS,
+ bool IsLittleEndian) {
+ return llvm::make_unique<ELFDwoObjectWriter>(std::move(MOTW), OS, DwoOS,
+ IsLittleEndian);
+}
diff --git a/llvm/lib/MC/MCAsmBackend.cpp b/llvm/lib/MC/MCAsmBackend.cpp
index 213ea52..3119bb9 100644
--- a/llvm/lib/MC/MCAsmBackend.cpp
+++ b/llvm/lib/MC/MCAsmBackend.cpp
@@ -49,6 +49,16 @@
}
}
+std::unique_ptr<MCObjectWriter>
+MCAsmBackend::createDwoObjectWriter(raw_pwrite_stream &OS,
+ raw_pwrite_stream &DwoOS) const {
+ auto TW = createObjectTargetWriter();
+ if (TW->getFormat() != Triple::ELF)
+ report_fatal_error("dwo only supported with ELF");
+ return createELFDwoObjectWriter(cast<MCELFObjectTargetWriter>(std::move(TW)),
+ OS, DwoOS, Endian == support::little);
+}
+
Optional<MCFixupKind> MCAsmBackend::getFixupKind(StringRef Name) const {
return None;
}