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[BOLT] Speedup PLT processing

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Summary:
With larger PLT sizes, linear PLT symbol name lookup becomes a
bottleneck.

(cherry picked from FBD21223695)
This commit is contained in:
Maksim Panchenko
2020-04-23 21:29:10 -07:00
parent 0ea98d1f0b
commit fbca177a83
1 changed files with 35 additions and 33 deletions
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68
bolt/src/RewriteInstance.cpp
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@@ -1299,16 +1299,28 @@ void RewriteInstance::disassemblePLT() {
// Used to analyze both the .plt section (most common) and the less common
// .plt.got created by the BFD linker.
auto analyzeOnePLTSection = [&](BinarySection &Section,
BinarySection *RelocsSection,
const BinarySection &RelocsSection,
uint64_t RelocType, uint64_t EntrySize) {
const auto PLTAddress = Section.getAddress();
StringRef PLTContents = Section.getContents();
ArrayRef<uint8_t> PLTData(
reinterpret_cast<const uint8_t *>(PLTContents.data()),
Section.getSize());
const auto PtrSize = BC->AsmInfo->getCodePointerSize();
for (uint64_t Offset = 0; Offset < Section.getSize();
Offset += EntrySize) {
// Runtime linker will put a value of an external symbol at the location
// referenced by the relocation. Map the address to the name of the symbol.
std::unordered_map<uint64_t, StringRef> RelAddrToNameMap;
for (const auto &Rel : RelocsSection.getSectionRef().relocations()) {
if (Rel.getType() != RelocType)
continue;
const auto SymbolIter = Rel.getSymbol();
assert(SymbolIter != InputFile->symbol_end() &&
"non-null symbol expected");
RelAddrToNameMap[Rel.getOffset()] = cantFail((*SymbolIter).getName());
}
for (uint64_t Offset = 0; Offset < Section.getSize(); Offset += EntrySize) {
uint64_t InstrSize;
MCInst Instruction;
const uint64_t InstrAddr = PLTAddress + Offset;
@@ -1332,30 +1344,19 @@ void RewriteInstance::disassemblePLT() {
<< Twine::utohexstr(InstrAddr) << '\n';
exit(1);
}
auto NI = RelAddrToNameMap.find(TargetAddress);
if (NI == RelAddrToNameMap.end())
continue;
// To get the name we have to read a relocation against the address.
if (RelocsSection) {
for (const auto &Rel : RelocsSection->getSectionRef().relocations()) {
if (Rel.getType() != RelocType)
continue;
if (Rel.getOffset() == TargetAddress) {
const auto SymbolIter = Rel.getSymbol();
assert(SymbolIter != InputFile->symbol_end() &&
"non-null symbol expected");
const auto SymbolName = cantFail((*SymbolIter).getName());
std::string Name = SymbolName.str() + "@PLT";
const auto PtrSize = BC->AsmInfo->getCodePointerSize();
auto *BF = BC->createBinaryFunction(Name, Section, InstrAddr, 0,
/*IsSimple=*/false, EntrySize,
PLTAlignment);
auto TargetSymbol =
BC->registerNameAtAddress(SymbolName.str() + "@GOT",
TargetAddress, PtrSize, PLTAlignment);
BF->setPLTSymbol(TargetSymbol);
break;
}
}
}
StringRef SymbolName = NI->second;
auto *BF = BC->createBinaryFunction(SymbolName.str() + "@PLT", Section,
InstrAddr, 0, /*IsSimple=*/false,
EntrySize, PLTAlignment);
MCSymbol *TargetSymbol =
BC->registerNameAtAddress(SymbolName.str() + "@GOT",
TargetAddress, PtrSize, PLTAlignment);
BF->setPLTSymbol(TargetSymbol);
}
};
@@ -1365,16 +1366,17 @@ void RewriteInstance::disassemblePLT() {
BC->createBinaryFunction("__BOLT_PLT_PSEUDO", *PLTSection,
PLTSection->getAddress(), 0, false, PLTSize,
PLTAlignment);
analyzeOnePLTSection(*PLTSection,
RelaPLTSection ? &*RelaPLTSection : nullptr,
ELF::R_X86_64_JUMP_SLOT, PLTSize);
if (RelaPLTSection) {
analyzeOnePLTSection(*PLTSection, *RelaPLTSection,
ELF::R_X86_64_JUMP_SLOT, PLTSize);
}
}
if (PLTGOTSection) {
analyzeOnePLTSection(*PLTGOTSection,
RelaDynSection ? &*RelaDynSection : nullptr,
ELF::R_X86_64_GLOB_DAT,
/*Size=*/8);
if (RelaDynSection) {
analyzeOnePLTSection(*PLTGOTSection, *RelaDynSection,
ELF::R_X86_64_GLOB_DAT, /*Size=*/8);
}
// If we did not register any function at PLTGOT start, we may be missing
// relocs. Add a function at the start to mark this section.
if (BC->getBinaryFunctions().find(PLTGOTSection->getAddress()) ==