From 3367c24735c3408517c6088061eee39030a69e70 Mon Sep 17 00:00:00 2001 From: Nicolas Miller Date: Sat, 19 Feb 2022 20:29:08 +0200 Subject: [PATCH] [COFF] Move section name encoding into BinaryFormat Large COFF section names are moved into the string table and the section header field is the offset into the string table encoded in ASCII for offset smaller than 7 digits and in base64 for larger offsets. The operation of taking the string table offsets is done in a few places in the codebase, so it is helpful to move this operation into `BinaryFormat` so that it can be shared everywhere it's done. So this patch takes the implementation of this operation from `llvm/lib/MC/WinCOFFObjectWriter.cpp` and moves it into `BinaryFormat`. Reviewed By: jhenderson, rnk Differential Revision: https://reviews.llvm.org/D118793 (cherry picked from commit 85f4023e731c0c42e45bf32bfcbf5f73c2013384) --- llvm/include/llvm/BinaryFormat/COFF.h | 4 ++ llvm/lib/BinaryFormat/CMakeLists.txt | 1 + llvm/lib/BinaryFormat/COFF.cpp | 57 +++++++++++++++++++++++++++ llvm/lib/MC/WinCOFFObjectWriter.cpp | 41 +------------------ 4 files changed, 64 insertions(+), 39 deletions(-) create mode 100644 llvm/lib/BinaryFormat/COFF.cpp diff --git a/llvm/include/llvm/BinaryFormat/COFF.h b/llvm/include/llvm/BinaryFormat/COFF.h index e7dde986784f7..016fe02894065 100644 --- a/llvm/include/llvm/BinaryFormat/COFF.h +++ b/llvm/include/llvm/BinaryFormat/COFF.h @@ -731,6 +731,10 @@ inline bool isReservedSectionNumber(int32_t SectionNumber) { return SectionNumber <= 0; } +/// Encode section name based on string table offset. +/// The size of Out must be at least COFF::NameSize. +bool encodeSectionName(char *Out, uint64_t Offset); + } // End namespace COFF. } // End namespace llvm. diff --git a/llvm/lib/BinaryFormat/CMakeLists.txt b/llvm/lib/BinaryFormat/CMakeLists.txt index 37f6865a487e8..50c1713804368 100644 --- a/llvm/lib/BinaryFormat/CMakeLists.txt +++ b/llvm/lib/BinaryFormat/CMakeLists.txt @@ -1,5 +1,6 @@ add_llvm_component_library(LLVMBinaryFormat AMDGPUMetadataVerifier.cpp + COFF.cpp Dwarf.cpp ELF.cpp MachO.cpp diff --git a/llvm/lib/BinaryFormat/COFF.cpp b/llvm/lib/BinaryFormat/COFF.cpp new file mode 100644 index 0000000000000..8fbee0218b79b --- /dev/null +++ b/llvm/lib/BinaryFormat/COFF.cpp @@ -0,0 +1,57 @@ +//===- llvm/BinaryFormat/COFF.cpp - The COFF format -----------------------===// +// +// 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 +// +//===----------------------------------------------------------------------===// + +#include "llvm/BinaryFormat/COFF.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Twine.h" + +// Maximum offsets for different string table entry encodings. +enum : unsigned { Max7DecimalOffset = 9999999U }; +enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0 + +// Encode a string table entry offset in base 64, padded to 6 chars, and +// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ... +// Buffer must be at least 8 bytes large. No terminating null appended. +static void encodeBase64StringEntry(char *Buffer, uint64_t Value) { + assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset && + "Illegal section name encoding for value"); + + static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + "abcdefghijklmnopqrstuvwxyz" + "0123456789+/"; + + Buffer[0] = '/'; + Buffer[1] = '/'; + + char *Ptr = Buffer + 7; + for (unsigned i = 0; i < 6; ++i) { + unsigned Rem = Value % 64; + Value /= 64; + *(Ptr--) = Alphabet[Rem]; + } +} + +bool llvm::COFF::encodeSectionName(char *Out, uint64_t Offset) { + if (Offset <= Max7DecimalOffset) { + // Offsets of 7 digits or less are encoded in ASCII. + SmallVector Buffer; + Twine('/').concat(Twine(Offset)).toVector(Buffer); + assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2); + std::memcpy(Out, Buffer.data(), Buffer.size()); + return true; + } + + if (Offset <= MaxBase64Offset) { + // Starting with 10,000,000, offsets are encoded as base64. + encodeBase64StringEntry(Out, Offset); + return true; + } + + // The offset is too large to be encoded. + return false; +} diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp index 73c687331d300..aba2ad3155356 100644 --- a/llvm/lib/MC/WinCOFFObjectWriter.cpp +++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp @@ -452,32 +452,6 @@ void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &MCSym, Sym->MC = &MCSym; } -// Maximum offsets for different string table entry encodings. -enum : unsigned { Max7DecimalOffset = 9999999U }; -enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0 - -// Encode a string table entry offset in base 64, padded to 6 chars, and -// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ... -// Buffer must be at least 8 bytes large. No terminating null appended. -static void encodeBase64StringEntry(char *Buffer, uint64_t Value) { - assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset && - "Illegal section name encoding for value"); - - static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" - "abcdefghijklmnopqrstuvwxyz" - "0123456789+/"; - - Buffer[0] = '/'; - Buffer[1] = '/'; - - char *Ptr = Buffer + 7; - for (unsigned i = 0; i < 6; ++i) { - unsigned Rem = Value % 64; - Value /= 64; - *(Ptr--) = Alphabet[Rem]; - } -} - void WinCOFFObjectWriter::SetSectionName(COFFSection &S) { if (S.Name.size() <= COFF::NameSize) { std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size()); @@ -485,19 +459,8 @@ void WinCOFFObjectWriter::SetSectionName(COFFSection &S) { } uint64_t StringTableEntry = Strings.getOffset(S.Name); - if (StringTableEntry <= Max7DecimalOffset) { - SmallVector Buffer; - Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer); - assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2); - std::memcpy(S.Header.Name, Buffer.data(), Buffer.size()); - return; - } - if (StringTableEntry <= MaxBase64Offset) { - // Starting with 10,000,000, offsets are encoded as base64. - encodeBase64StringEntry(S.Header.Name, StringTableEntry); - return; - } - report_fatal_error("COFF string table is greater than 64 GB."); + if (!COFF::encodeSectionName(S.Header.Name, StringTableEntry)) + report_fatal_error("COFF string table is greater than 64 GB."); } void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {