Keep start and stop symbols linked through clang (Linux) #8214
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Changes in https://reviews.llvm.org/D96914 taught LLD to remove `__start_##name` and `__stop_##name` symbol names. The Swift runtime uses these specially named symbols to unpack the runtime type metadata on Linux and WebAssembly systems, resulting in broken binaries when linked with `lld`. This change tells the Swift-paired Clang to force the `-z nostart-stop-gc` flag when compiling for Linux-y systems, including Musl, WASM, and Android. Swift and the clang-linker have to work with other existing toolchains, so we can't simply flip the cmake option in the LLVM build system to keep these symbols and get a working binary.
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@swift-ci please test |
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I have checked this manually with |
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I think that you can add a test in |
| @@ -836,7 +836,7 @@ std::string ToolChain::GetLinkerPath(bool *LinkerIsLLD) const { | |||
| if (llvm::sys::fs::can_execute(UseLinker)) | |||
| return std::string(UseLinker); | |||
| } else { | |||
| llvm::SmallString<8> LinkerName; | |||
| llvm::SmallString<8> LinkerName = {}; | |||
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This seems unnecessary? Would be nice to stay as close to upstream as possible.
| bool useLLD = false; | ||
| const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath(&useLLD)); | ||
| if (useLLD) { |
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Why not if (Args.hasArg(options::OPT_fuse_ld_EQ) && Args.getLastArgValue(options::OPT_fuse_ld_EQ).ends_with_insensitive("lld"))?
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Yeah, mainly to support when someone isn't passing --fuse-ld=lld. It should still catch it if clang was configured to use lld by default. We're already calling GetLinkerPath, which is also conveniently supposed to detect when the linker is lld either through clang being configured to use lld by default, --fuse-ld=lld, or --ld-path=<filepath>/ld.lld.
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I prefer swiftlang/swift#72061 to resolve this issue. |
Changes in https://reviews.llvm.org/D96914 taught LLD to remove
__start_##nameand__stop_##namesymbol names. The Swift runtime uses these specially named symbols to unpack the runtime type metadata on Linux and WebAssembly systems, resulting in broken binaries when linked withlld. This change tells the Swift-paired Clang to force the-z nostart-stop-gcflag when compiling for Linux-y systems, including Musl, WASM, and Android. Swift and the clang-linker have to work with other existing toolchains, so we can't simply flip the CMake option in the LLVM build system to keep these symbols and get a working binary.