From 1813fde9cc0b56cee42d9b82e6f22fa00a59cdf9 Mon Sep 17 00:00:00 2001 From: Yuta Saito Date: Tue, 19 Oct 2021 15:42:00 -0700 Subject: [PATCH] [WebAssembly] Emit clangast in custom section aligned by 4 bytes Emit __clangast in custom section instead of named data segment to find it while iterating sections. This could be avoided if all data segements (the wasm sense) were represented as their own sections (in the llvm sense). This can be resolved by https://github.com/WebAssembly/tool-conventions/issues/138 And the on-disk hashtable in clangast needs to be aligned by 4 bytes, so add paddings in name length field in custom section header. The length of clangast section name can be represented in 1 byte by leb128, and possible maximum pads are 3 bytes, so the section name length won't be invalid in theory. Fixes https://bugs.llvm.org/show_bug.cgi?id=35928 Differential Revision: https://reviews.llvm.org/D74531 --- .../ObjectFilePCHContainerOperations.cpp | 53 ++++++++++++------- clang/test/PCH/pch-wasm.c | 7 +++ llvm/lib/MC/WasmObjectWriter.cpp | 31 ++++++++++- .../WebAssembly/custom-section-alignment.ll | 10 ++++ 4 files changed, 82 insertions(+), 19 deletions(-) create mode 100644 clang/test/PCH/pch-wasm.c create mode 100644 llvm/test/MC/WebAssembly/custom-section-alignment.ll diff --git a/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp b/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp index ce45291af3b8..f7b83c45022d 100644 --- a/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp +++ b/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp @@ -270,25 +270,42 @@ public: assert(Buffer->IsComplete && "serialization did not complete"); auto &SerializedAST = Buffer->Data; auto Size = SerializedAST.size(); - auto Int8Ty = llvm::Type::getInt8Ty(*VMContext); - auto *Ty = llvm::ArrayType::get(Int8Ty, Size); - auto *Data = llvm::ConstantDataArray::getString( - *VMContext, StringRef(SerializedAST.data(), Size), - /*AddNull=*/false); - auto *ASTSym = new llvm::GlobalVariable( - *M, Ty, /*constant*/ true, llvm::GlobalVariable::InternalLinkage, Data, - "__clang_ast"); - // The on-disk hashtable needs to be aligned. - ASTSym->setAlignment(llvm::Align(8)); - // Mach-O also needs a segment name. - if (Triple.isOSBinFormatMachO()) - ASTSym->setSection("__CLANG,__clangast"); - // COFF has an eight character length limit. - else if (Triple.isOSBinFormatCOFF()) - ASTSym->setSection("clangast"); - else - ASTSym->setSection("__clangast"); + if (Triple.isOSBinFormatWasm()) { + // Emit __clangast in custom section instead of named data segment + // to find it while iterating sections. + // This could be avoided if all data segements (the wasm sense) were + // represented as their own sections (in the llvm sense). + // TODO: https://github.com/WebAssembly/tool-conventions/issues/138 + llvm::NamedMDNode *MD = + M->getOrInsertNamedMetadata("wasm.custom_sections"); + llvm::Metadata *Ops[2] = { + llvm::MDString::get(*VMContext, "__clangast"), + llvm::MDString::get(*VMContext, + StringRef(SerializedAST.data(), Size))}; + auto *NameAndContent = llvm::MDTuple::get(*VMContext, Ops); + MD->addOperand(NameAndContent); + } else { + auto Int8Ty = llvm::Type::getInt8Ty(*VMContext); + auto *Ty = llvm::ArrayType::get(Int8Ty, Size); + auto *Data = llvm::ConstantDataArray::getString( + *VMContext, StringRef(SerializedAST.data(), Size), + /*AddNull=*/false); + auto *ASTSym = new llvm::GlobalVariable( + *M, Ty, /*constant*/ true, llvm::GlobalVariable::InternalLinkage, + Data, "__clang_ast"); + // The on-disk hashtable needs to be aligned. + ASTSym->setAlignment(llvm::Align(8)); + + // Mach-O also needs a segment name. + if (Triple.isOSBinFormatMachO()) + ASTSym->setSection("__CLANG,__clangast"); + // COFF has an eight character length limit. + else if (Triple.isOSBinFormatCOFF()) + ASTSym->setSection("clangast"); + else + ASTSym->setSection("__clangast"); + } LLVM_DEBUG({ // Print the IR for the PCH container to the debug output. diff --git a/clang/test/PCH/pch-wasm.c b/clang/test/PCH/pch-wasm.c new file mode 100644 index 000000000000..c8df80a9fa5f --- /dev/null +++ b/clang/test/PCH/pch-wasm.c @@ -0,0 +1,7 @@ +// REQUIRES: webassembly-registered-target +// RUN: %clang_cc1 -triple wasm32-unknown-unknown-wasm -emit-pch -fmodule-format=obj %S/pchpch1.h -o - | llvm-objdump --section-headers - | FileCheck %s + +// Ensure that clangast section should be emitted in a section for wasm object file + +// CHECK: file format wasm +// CHECK: __clangast {{[0-9a-f]+}} {{[0-9a-f]+}} diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp index 707a3f625db7..015931ba4cac 100644 --- a/llvm/lib/MC/WasmObjectWriter.cpp +++ b/llvm/lib/MC/WasmObjectWriter.cpp @@ -292,6 +292,8 @@ private: W->OS << Str; } + void writeStringWithAlignment(const StringRef Str, unsigned Alignment); + void writeI32(int32_t val) { char Buffer[4]; support::endian::write32le(Buffer, val); @@ -362,6 +364,28 @@ void WasmObjectWriter::startSection(SectionBookkeeping &Section, Section.Index = SectionCount++; } +// Write a string with extra paddings for trailing alignment +// TODO: support alignment at asm and llvm level? +void WasmObjectWriter::writeStringWithAlignment(const StringRef Str, + unsigned Alignment) { + + // Calculate the encoded size of str length and add pads based on it and + // alignment. + raw_null_ostream NullOS; + uint64_t StrSizeLength = encodeULEB128(Str.size(), NullOS); + uint64_t Offset = W->OS.tell() + StrSizeLength + Str.size(); + uint64_t Paddings = offsetToAlignment(Offset, Align(Alignment)); + Offset += Paddings; + + // LEB128 greater than 5 bytes is invalid + assert((StrSizeLength + Paddings) <= 5 && "too long string to align"); + + encodeSLEB128(Str.size(), W->OS, StrSizeLength + Paddings); + W->OS << Str; + + assert(W->OS.tell() == Offset && "invalid padding"); +} + void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section, StringRef Name) { LLVM_DEBUG(dbgs() << "startCustomSection " << Name << "\n"); @@ -371,7 +395,12 @@ void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section, Section.PayloadOffset = W->OS.tell(); // Custom sections in wasm also have a string identifier. - writeString(Name); + if (Name != "__clangast") { + writeString(Name); + } else { + // The on-disk hashtable in clangast needs to be aligned by 4 bytes. + writeStringWithAlignment(Name, 4); + } // The position where the custom section starts. Section.ContentsOffset = W->OS.tell(); diff --git a/llvm/test/MC/WebAssembly/custom-section-alignment.ll b/llvm/test/MC/WebAssembly/custom-section-alignment.ll new file mode 100644 index 000000000000..690bc90feb1e --- /dev/null +++ b/llvm/test/MC/WebAssembly/custom-section-alignment.ll @@ -0,0 +1,10 @@ +; RUN: llc -filetype=obj %s -o - | od -t x1 -v | FileCheck %s + +target triple = "wasm32-unknown-unknown" + +!0 = !{ !"before", !"\de\ad\be\ef" } +!1 = !{ !"__clangast", !"\fe\ed\fa\ce" } +!wasm.custom_sections = !{ !0, !1 } + +; Ensure that __clangast content is aligned by 4 bytes +; CHECK: {{(([0-9a-f]{2} ){4})*}}fe ed fa ce