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//===- bolt/Rewrite/RSeqRewriter.cpp --------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Basic support for restartable sequences used by tcmalloc. Prevent critical
// section overrides by ignoring optimizations in containing functions.
//
// References:
// * https://google.github.io/tcmalloc/rseq.html
// * tcmalloc/internal/percpu_rseq_x86_64.S
//
//===----------------------------------------------------------------------===//
#include "bolt/Core/BinaryFunction.h"
#include "bolt/Rewrite/MetadataRewriter.h"
#include "bolt/Rewrite/MetadataRewriters.h"
#include "llvm/Support/Errc.h"
using namespace llvm;
using namespace bolt;
namespace {
class RSeqRewriter final : public MetadataRewriter {
public:
RSeqRewriter(StringRef Name, BinaryContext &BC)
: MetadataRewriter(Name, BC) {}
Error preCFGInitializer() override {
for (const BinarySection &Section : BC.allocatableSections()) {
if (Section.getName() != "__rseq_cs")
continue;
auto handleRelocation = [&](const Relocation &Rel, bool IsDynamic) {
BinaryFunction *BF = nullptr;
if (Rel.Symbol)
BF = BC.getFunctionForSymbol(Rel.Symbol);
else if (Relocation::isRelative(Rel.Type))
BF = BC.getBinaryFunctionContainingAddress(Rel.Addend);
if (!BF) {
BC.errs() << "BOLT-WARNING: no function found matching "
<< (IsDynamic ? "dynamic " : "")
<< "relocation in __rseq_cs\n";
} else if (!BF->isIgnored()) {
BC.outs() << "BOLT-INFO: restartable sequence reference detected in "
<< *BF << ". Function will not be optimized\n";
BF->setIgnored();
}
};
for (const Relocation &Rel : Section.dynamicRelocations())
handleRelocation(Rel, /*IsDynamic*/ true);
for (const Relocation &Rel : Section.relocations())
handleRelocation(Rel, /*IsDynamic*/ false);
}
return Error::success();
}
};
} // namespace
std::unique_ptr<MetadataRewriter>
llvm::bolt::createRSeqRewriter(BinaryContext &BC) {
return std::make_unique<RSeqRewriter>("rseq-cs-rewriter", BC);
}
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