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[BOLT] Use rewriter interface for updating binary build ID (llvm#94273)
Move functionality for patching build ID into a separate rewriter class and change the way we do the patching. Support build ID in different note sections in order to update the build ID in the Linux kernel binary which puts in into ".notes" section instead of ".note.gnu.build-id".
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,113 @@ | ||
| //===- bolt/Rewrite/BuildIDRewriter.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 | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // Read and update build ID stored in ELF note section. | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #include "bolt/Rewrite/MetadataRewriter.h" | ||
| #include "bolt/Rewrite/MetadataRewriters.h" | ||
| #include "llvm/Support/Errc.h" | ||
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| using namespace llvm; | ||
| using namespace bolt; | ||
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| namespace { | ||
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| /// The build-id is typically a stream of 20 bytes. Return these bytes in | ||
| /// printable hexadecimal form. | ||
| std::string getPrintableBuildID(StringRef BuildID) { | ||
| std::string Str; | ||
| raw_string_ostream OS(Str); | ||
| for (const char &Char : BuildID) | ||
| OS << format("%.2x", static_cast<unsigned char>(Char)); | ||
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| return OS.str(); | ||
| } | ||
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| class BuildIDRewriter final : public MetadataRewriter { | ||
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| /// Information about binary build ID. | ||
| ErrorOr<BinarySection &> BuildIDSection{std::errc::bad_address}; | ||
| StringRef BuildID; | ||
| std::optional<uint64_t> BuildIDOffset; | ||
| std::optional<uint64_t> BuildIDSize; | ||
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| public: | ||
| BuildIDRewriter(StringRef Name, BinaryContext &BC) | ||
| : MetadataRewriter(Name, BC) {} | ||
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| Error sectionInitializer() override; | ||
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| Error postEmitFinalizer() override; | ||
| }; | ||
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| Error BuildIDRewriter::sectionInitializer() { | ||
| // Typically, build ID will reside in .note.gnu.build-id section. Howerver, | ||
| // a linker script can change the section name and such is the case with | ||
| // the Linux kernel. Hence, we iterate over all note sections. | ||
| for (BinarySection &NoteSection : BC.sections()) { | ||
| if (!NoteSection.isNote()) | ||
| continue; | ||
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| StringRef Buf = NoteSection.getContents(); | ||
| DataExtractor DE = DataExtractor(Buf, BC.AsmInfo->isLittleEndian(), | ||
| BC.AsmInfo->getCodePointerSize()); | ||
| DataExtractor::Cursor Cursor(0); | ||
| while (Cursor && !DE.eof(Cursor)) { | ||
| const uint32_t NameSz = DE.getU32(Cursor); | ||
| const uint32_t DescSz = DE.getU32(Cursor); | ||
| const uint32_t Type = DE.getU32(Cursor); | ||
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| StringRef Name = | ||
| NameSz ? Buf.slice(Cursor.tell(), Cursor.tell() + NameSz) : "<empty>"; | ||
| Cursor.seek(alignTo(Cursor.tell() + NameSz, 4)); | ||
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| const uint64_t DescOffset = Cursor.tell(); | ||
| StringRef Desc = | ||
| DescSz ? Buf.slice(DescOffset, DescOffset + DescSz) : "<empty>"; | ||
| Cursor.seek(alignTo(DescOffset + DescSz, 4)); | ||
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| if (!Cursor) | ||
| return createStringError(errc::executable_format_error, | ||
| "out of bounds while reading note section: %s", | ||
| toString(Cursor.takeError()).c_str()); | ||
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| if (Type == ELF::NT_GNU_BUILD_ID && Name.substr(0, 3) == "GNU" && | ||
| DescSz) { | ||
| BuildIDSection = NoteSection; | ||
| BuildID = Desc; | ||
| BC.setFileBuildID(getPrintableBuildID(Desc)); | ||
| BuildIDOffset = DescOffset; | ||
| BuildIDSize = DescSz; | ||
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| return Error::success(); | ||
| } | ||
| } | ||
| } | ||
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| return Error::success(); | ||
| } | ||
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| Error BuildIDRewriter::postEmitFinalizer() { | ||
| if (!BuildIDSection || !BuildIDOffset) | ||
| return Error::success(); | ||
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| const uint8_t LastByte = BuildID[BuildID.size() - 1]; | ||
| SmallVector<char, 1> Patch = {static_cast<char>(LastByte ^ 1)}; | ||
| BuildIDSection->addPatch(*BuildIDOffset + BuildID.size() - 1, Patch); | ||
| BC.outs() << "BOLT-INFO: patched build-id (flipped last bit)\n"; | ||
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| return Error::success(); | ||
| } | ||
| } // namespace | ||
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| std::unique_ptr<MetadataRewriter> | ||
| llvm::bolt::createBuildIDRewriter(BinaryContext &BC) { | ||
| return std::make_unique<BuildIDRewriter>("build-id-rewriter", BC); | ||
| } |
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