From 74b8d324eb77a8f337b35dc68ac91b0c2c06debc Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 29 May 2022 01:10:44 +0200 Subject: Support `.comment` section like GCC/Clang (`!llvm.ident`) Both GCC and Clang write by default a `.comment` section with compiler information: ```txt $ gcc -c -xc /dev/null && readelf -p '.comment' null.o String dump of section '.comment': [ 1] GCC: (GNU) 11.2.0 $ clang -c -xc /dev/null && readelf -p '.comment' null.o String dump of section '.comment': [ 1] clang version 14.0.1 (https://github.com/llvm/llvm-project.git c62053979489ccb002efe411c3af059addcb5d7d) ``` They also implement the `-Qn` flag to avoid doing so: ```txt $ gcc -Qn -c -xc /dev/null && readelf -p '.comment' null.o readelf: Warning: Section '.comment' was not dumped because it does not exist! $ clang -Qn -c -xc /dev/null && readelf -p '.comment' null.o readelf: Warning: Section '.comment' was not dumped because it does not exist! ``` So far, `rustc` only does it for WebAssembly targets and only when debug info is enabled: ```txt $ echo 'fn main(){}' | rustc --target=wasm32-unknown-unknown --emit=llvm-ir -Cdebuginfo=2 - && grep llvm.ident rust_out.ll !llvm.ident = !{!27} ``` In the RFC part of this PR it was decided to always add the information, which gets us closer to other popular compilers. An opt-out flag like GCC and Clang may be added later on if deemed necessary. Implementation-wise, this covers both `ModuleLlvm::new()` and `ModuleLlvm::new_metadata()` cases by moving the addition to `context::create_module` and adds a few test cases. ThinLTO also sees the `llvm.ident` named metadata duplicated (in temporary outputs), so this deduplicates it like it is done for `wasm.custom_sections`. The tests also check this duplication does not take place. Signed-off-by: Miguel Ojeda --- compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp') diff --git a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp index e5fb6b0953f..71df17c9ce7 100644 --- a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp +++ b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp @@ -1366,6 +1366,11 @@ LLVMRustPrepareThinLTOImport(const LLVMRustThinLTOData *Data, LLVMModuleRef M, if (WasmCustomSections) WasmCustomSections->eraseFromParent(); + // `llvm.ident` named metadata also gets duplicated. + auto *llvmIdent = (*MOrErr)->getNamedMetadata("llvm.ident"); + if (llvmIdent) + llvmIdent->eraseFromParent(); + return MOrErr; }; bool ClearDSOLocal = clearDSOLocalOnDeclarations(Mod, Target); -- cgit 1.4.1-3-g733a5