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| 1 | +//===- bolt/Rewrite/GNUPropertyRewriter.cpp -------------------------------===// |
| 2 | +// |
| 3 | +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | +// See https://llvm.org/LICENSE.txt for license information. |
| 5 | +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | +// |
| 7 | +//===----------------------------------------------------------------------===// |
| 8 | +// |
| 9 | +// Read the .note.gnu.property section. |
| 10 | +// |
| 11 | +//===----------------------------------------------------------------------===// |
| 12 | + |
| 13 | +#include "bolt/Rewrite/MetadataRewriter.h" |
| 14 | +#include "bolt/Rewrite/MetadataRewriters.h" |
| 15 | +#include "llvm/Support/Errc.h" |
| 16 | + |
| 17 | +using namespace llvm; |
| 18 | +using namespace bolt; |
| 19 | + |
| 20 | +namespace { |
| 21 | + |
| 22 | +class GNUPropertyRewriter final : public MetadataRewriter { |
| 23 | + |
| 24 | + Expected<uint32_t> decodeGNUPropertyNote(StringRef Desc); |
| 25 | + |
| 26 | +public: |
| 27 | + GNUPropertyRewriter(StringRef Name, BinaryContext &BC) |
| 28 | + : MetadataRewriter(Name, BC) {} |
| 29 | + |
| 30 | + Error sectionInitializer() override; |
| 31 | +}; |
| 32 | + |
| 33 | +Error GNUPropertyRewriter::sectionInitializer() { |
| 34 | + |
| 35 | + ErrorOr<BinarySection &> Sec = |
| 36 | + BC.getUniqueSectionByName(".note.gnu.property"); |
| 37 | + if (!Sec) |
| 38 | + return Error::success(); |
| 39 | + |
| 40 | + // Accumulate feature bits |
| 41 | + uint32_t FeaturesAcc = 0; |
| 42 | + |
| 43 | + StringRef Buf = Sec->getContents(); |
| 44 | + DataExtractor DE(Buf, BC.AsmInfo->isLittleEndian(), |
| 45 | + BC.AsmInfo->getCodePointerSize()); |
| 46 | + DataExtractor::Cursor Cursor(0); |
| 47 | + while (Cursor && !DE.eof(Cursor)) { |
| 48 | + const uint32_t NameSz = DE.getU32(Cursor); |
| 49 | + const uint32_t DescSz = DE.getU32(Cursor); |
| 50 | + const uint32_t Type = DE.getU32(Cursor); |
| 51 | + |
| 52 | + StringRef Name = |
| 53 | + NameSz ? Buf.slice(Cursor.tell(), Cursor.tell() + NameSz) : "<empty>"; |
| 54 | + Cursor.seek(alignTo(Cursor.tell() + NameSz, 4)); |
| 55 | + |
| 56 | + const uint64_t DescOffset = Cursor.tell(); |
| 57 | + StringRef Desc = |
| 58 | + DescSz ? Buf.slice(DescOffset, DescOffset + DescSz) : "<empty>"; |
| 59 | + Cursor.seek(alignTo(DescOffset + DescSz, 4)); |
| 60 | + if (!Cursor) |
| 61 | + return createStringError( |
| 62 | + errc::executable_format_error, |
| 63 | + "out of bounds while reading .note.gnu.property section: %s", |
| 64 | + toString(Cursor.takeError()).c_str()); |
| 65 | + |
| 66 | + if (Type == ELF::NT_GNU_PROPERTY_TYPE_0 && Name.starts_with("GNU") && |
| 67 | + DescSz) { |
| 68 | + auto Features = decodeGNUPropertyNote(Desc); |
| 69 | + if (!Features) |
| 70 | + return Features.takeError(); |
| 71 | + FeaturesAcc |= *Features; |
| 72 | + } |
| 73 | + } |
| 74 | + |
| 75 | + if (BC.isAArch64()) { |
| 76 | + BC.setUsesBTI(FeaturesAcc & llvm::ELF::GNU_PROPERTY_AARCH64_FEATURE_1_BTI); |
| 77 | + if (BC.usesBTI()) |
| 78 | + BC.outs() << "BOLT-WARNING: binary is using BTI. Optimized binary may be " |
| 79 | + "corrupted\n"; |
| 80 | + } |
| 81 | + |
| 82 | + return Error::success(); |
| 83 | +} |
| 84 | + |
| 85 | +/// \p Desc contains an array of property descriptors. Each member has the |
| 86 | +/// following structure: |
| 87 | +/// typedef struct { |
| 88 | +/// Elf_Word pr_type; |
| 89 | +/// Elf_Word pr_datasz; |
| 90 | +/// unsigned char pr_data[PR_DATASZ]; |
| 91 | +/// unsigned char pr_padding[PR_PADDING]; |
| 92 | +/// } Elf_Prop; |
| 93 | +/// |
| 94 | +/// As there is no guarantee that the features are encoded in which element of |
| 95 | +/// the array, we have to read all, and OR together the result. |
| 96 | +Expected<uint32_t> GNUPropertyRewriter::decodeGNUPropertyNote(StringRef Desc) { |
| 97 | + DataExtractor DE(Desc, BC.AsmInfo->isLittleEndian(), |
| 98 | + BC.AsmInfo->getCodePointerSize()); |
| 99 | + DataExtractor::Cursor Cursor(0); |
| 100 | + const uint32_t Align = DE.getAddressSize(); |
| 101 | + |
| 102 | + std::optional<uint32_t> Features = 0; |
| 103 | + while (Cursor && !DE.eof(Cursor)) { |
| 104 | + const uint32_t PrType = DE.getU32(Cursor); |
| 105 | + const uint32_t PrDataSz = DE.getU32(Cursor); |
| 106 | + |
| 107 | + const uint64_t PrDataStart = Cursor.tell(); |
| 108 | + const uint64_t PrDataEnd = PrDataStart + PrDataSz; |
| 109 | + Cursor.seek(PrDataEnd); |
| 110 | + if (!Cursor) |
| 111 | + return createStringError( |
| 112 | + errc::executable_format_error, |
| 113 | + "out of bounds while reading .note.gnu.property section: %s", |
| 114 | + toString(Cursor.takeError()).c_str()); |
| 115 | + |
| 116 | + if (PrType == llvm::ELF::GNU_PROPERTY_AARCH64_FEATURE_1_AND) { |
| 117 | + if (PrDataSz != 4) { |
| 118 | + return createStringError( |
| 119 | + errc::executable_format_error, |
| 120 | + "Property descriptor size has to be 4 bytes on AArch64\n"); |
| 121 | + } |
| 122 | + DataExtractor::Cursor Tmp(PrDataStart); |
| 123 | + // PrDataSz = 4 -> PrData is uint32_t |
| 124 | + const uint32_t FeaturesItem = DE.getU32(Tmp); |
| 125 | + if (!Tmp) |
| 126 | + return createStringError( |
| 127 | + errc::executable_format_error, |
| 128 | + "failed to read property from .note.gnu.property section: %s", |
| 129 | + toString(Tmp.takeError()).c_str()); |
| 130 | + Features = Features ? (*Features | FeaturesItem) : FeaturesItem; |
| 131 | + } |
| 132 | + |
| 133 | + Cursor.seek(alignTo(PrDataEnd, Align)); |
| 134 | + if (!Cursor) |
| 135 | + return createStringError(errc::executable_format_error, |
| 136 | + "out of bounds while reading property array in " |
| 137 | + ".note.gnu.property section: %s", |
| 138 | + toString(Cursor.takeError()).c_str()); |
| 139 | + } |
| 140 | + return Features.value_or(0u); |
| 141 | +} |
| 142 | +} // namespace |
| 143 | + |
| 144 | +std::unique_ptr<MetadataRewriter> |
| 145 | +llvm::bolt::createGNUPropertyRewriter(BinaryContext &BC) { |
| 146 | + return std::make_unique<GNUPropertyRewriter>("gnu-property-rewriter", BC); |
| 147 | +} |
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