Peter Collingbourne
8bc2258ab1
The current behavior, where .reloc directives are added to the end of the symbol's fragment's relocation list, is problematic because a fragment can be split at an arbitrary point (e.g. due to exceeding FragBlockSize), and if that point is in the middle of a relocation sequence such as TLSGD, that can result in an invalid sequence being emitted. To fix this, modify the behaviour to be closer to what GNU as does, by maintaining a .reloc group for each fragment while inserting .reloc relocations. A .reloc group is a consecutive sequence of .reloc relocations that have an offset <= the first relocation's offset. A relocation with offset > the first relocation's offset starts a new group. Relocation groups are inserted in offset order using the offset of the first relocation, but the source ordering of relocations within the group is preserved. Assisted-by: gemini (wrote initial version of llvm/test/MC/X86/reloc-directive-tlsgd.s) Reviewers: MaskRay Pull Request: https://github.com/llvm/llvm-project/pull/194065
123 lines
4.0 KiB
C++
123 lines
4.0 KiB
C++
//===- lib/MC/MCSection.cpp - Machine Code Section Representation ---------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/MC/MCSection.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Config/llvm-config.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCSymbol.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include <utility>
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using namespace llvm;
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MCSection::MCSection(StringRef Name, bool IsText, bool IsBss, MCSymbol *Begin)
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: Begin(Begin), HasInstructions(false), IsRegistered(false), IsText(IsText),
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IsBss(IsBss), Name(Name) {
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DummyFragment.setParent(this);
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}
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MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) {
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if (!End)
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End = Ctx.createTempSymbol("sec_end");
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return End;
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}
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bool MCSection::hasEnded() const { return End && End->isInSection(); }
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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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LLVM_DUMP_METHOD void MCSection::dump(
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DenseMap<const MCFragment *, SmallVector<const MCSymbol *, 0>> *FragToSyms)
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const {
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raw_ostream &OS = errs();
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OS << "MCSection Name:" << getName();
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if (isLinkerRelaxable())
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OS << " FirstLinkerRelaxable:" << firstLinkerRelaxable();
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for (auto &F : *this) {
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OS << '\n';
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F.dump();
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if (!FragToSyms)
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continue;
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auto It = FragToSyms->find(&F);
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if (It == FragToSyms->end())
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continue;
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for (auto *Sym : It->second) {
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OS << "\n Symbol @" << Sym->getOffset() << ' ' << Sym->getName();
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if (Sym->isTemporary())
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OS << " Temporary";
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}
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}
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}
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#endif
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void MCFragment::setVarContents(ArrayRef<char> Contents) {
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auto &S = getParent()->ContentStorage;
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if (VarContentStart + Contents.size() > VarContentEnd) {
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VarContentStart = S.size();
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S.resize_for_overwrite(S.size() + Contents.size());
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}
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VarContentEnd = VarContentStart + Contents.size();
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llvm::copy(Contents, S.begin() + VarContentStart);
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}
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void MCFragment::addFixup(MCFixup Fixup) { appendFixups({Fixup}); }
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void MCFragment::moveFixupsToEnd() {
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auto &S = getParent()->FixupStorage;
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if (LLVM_UNLIKELY(FixupEnd != S.size())) {
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// Move the elements to the end. Reserve space to avoid invalidating
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// S.begin()+I for `append`.
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auto Size = FixupEnd - FixupStart;
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auto I = std::exchange(FixupStart, S.size());
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S.reserve(S.size() + Size);
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S.append(S.begin() + I, S.begin() + I + Size);
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}
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}
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void MCFragment::appendFixups(ArrayRef<MCFixup> Fixups) {
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moveFixupsToEnd();
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auto &S = getParent()->FixupStorage;
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S.append(Fixups.begin(), Fixups.end());
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FixupEnd = S.size();
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}
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void MCFragment::insertRelocFixups(ArrayRef<MCFixup> Fixups) {
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moveFixupsToEnd();
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// See MCAssembler::layout() for the rule being followed here.
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auto &S = getParent()->FixupStorage;
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S.insert(std::upper_bound(S.begin() + FixupStart, S.end(), Fixups[0],
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[](MCFixup F1, MCFixup F2) {
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return F1.getOffset() < F2.getOffset();
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}),
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Fixups.begin(), Fixups.end());
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FixupEnd = S.size();
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}
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void MCFragment::setVarFixups(ArrayRef<MCFixup> Fixups) {
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assert(Fixups.size() < 256 &&
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"variable-size tail cannot have more than 256 fixups");
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auto &S = getParent()->FixupStorage;
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if (Fixups.size() > VarFixupSize) {
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VarFixupStart = S.size();
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S.resize_for_overwrite(S.size() + Fixups.size());
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}
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VarFixupSize = Fixups.size();
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// Source fixup offsets are relative to the variable part's start. Add the
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// fixed part size to make them relative to the fixed part's start.
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std::transform(Fixups.begin(), Fixups.end(), S.begin() + VarFixupStart,
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[Fixed = getFixedSize()](MCFixup F) {
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F.setOffset(Fixed + F.getOffset());
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return F;
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});
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}
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