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This flag causes wasm-ld to preserve features section even in the face
of `--strip-all`. This is useful for both clang (which can run
wasm-opt) after linking, and emcc (which performs a bunch of post-link
work).
Fixes: https://github.com/llvm/llvm-project/issues/60613
Fixes: https://github.com/llvm/llvm-project/issues/55781
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D149917
Files:
clang/lib/Driver/ToolChains/WebAssembly.cpp
lld/wasm/Config.h
lld/wasm/Driver.cpp
lld/wasm/Options.td
lld/wasm/SyntheticSections.h
Index: lld/wasm/SyntheticSections.h
===================================================================
--- lld/wasm/SyntheticSections.h
+++ lld/wasm/SyntheticSections.h
@@ -408,7 +408,8 @@
TargetFeaturesSection()
: SyntheticSection(llvm::wasm::WASM_SEC_CUSTOM, "target_features") {}
bool isNeeded() const override {
- return !config->stripAll && features.size() > 0;
+ return features.size() > 0 &&
+ (!config->stripAll || config->preserveFeatures);
}
void writeBody() override;
Index: lld/wasm/Options.td
===================================================================
--- lld/wasm/Options.td
+++ lld/wasm/Options.td
@@ -132,6 +132,8 @@
def strip_debug: F<"strip-debug">, HelpText<"Strip debugging information">;
+def preserve_features: F<"preserve-features">, HelpText<"Preserve features section even when --strip-all is given. This is useful for compiler drivers such as clang or emcc that depend on the features section for post-link processing.">;
+
defm threads
: Eq<"threads", "Number of threads. '1' disables multi-threading. By "
"default all available hardware threads are used">;
Index: lld/wasm/Driver.cpp
===================================================================
--- lld/wasm/Driver.cpp
+++ lld/wasm/Driver.cpp
@@ -476,6 +476,7 @@
args.hasFlag(OPT_merge_data_segments, OPT_no_merge_data_segments,
!config->relocatable);
config->pie = args.hasFlag(OPT_pie, OPT_no_pie, false);
+ config->preserveFeatures = args.hasArg(OPT_preserve_features);
config->printGcSections =
args.hasFlag(OPT_print_gc_sections, OPT_no_print_gc_sections, false);
config->saveTemps = args.hasArg(OPT_save_temps);
Index: lld/wasm/Config.h
===================================================================
--- lld/wasm/Config.h
+++ lld/wasm/Config.h
@@ -57,6 +57,7 @@
std::optional<bool> is64;
bool mergeDataSegments;
bool pie;
+ bool preserveFeatures;
bool printGcSections;
bool relocatable;
bool saveTemps;
Index: clang/lib/Driver/ToolChains/WebAssembly.cpp
===================================================================
--- clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -126,14 +126,25 @@
CmdArgs.push_back("-o");
CmdArgs.push_back(Output.getFilename());
+ // When optimizing, if wasm-opt is available, run it.
+ std::string WasmOptPath;
+ if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
+ WasmOptPath = ToolChain.GetProgramPath("wasm-opt");
+ if (WasmOptPath == "wasm-opt") {
+ WasmOptPath = {};
+ }
+ }
+
+ if (!WasmOptPath.empty()) {
+ CmdArgs.push_back("--preserve-features");
+ }
+
C.addCommand(std::make_unique<Command>(JA, *this,
ResponseFileSupport::AtFileCurCP(),
Linker, CmdArgs, Inputs, Output));
- // When optimizing, if wasm-opt is available, run it.
if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
- auto WasmOptPath = ToolChain.GetProgramPath("wasm-opt");
- if (WasmOptPath != "wasm-opt") {
+ if (!WasmOptPath.empty()) {
StringRef OOpt = "s";
if (A->getOption().matches(options::OPT_O4) ||
A->getOption().matches(options::OPT_Ofast))
@@ -145,13 +156,13 @@
if (OOpt != "0") {
const char *WasmOpt = Args.MakeArgString(WasmOptPath);
- ArgStringList CmdArgs;
- CmdArgs.push_back(Output.getFilename());
- CmdArgs.push_back(Args.MakeArgString(llvm::Twine("-O") + OOpt));
- CmdArgs.push_back("-o");
- CmdArgs.push_back(Output.getFilename());
+ ArgStringList OptArgs;
+ OptArgs.push_back(Output.getFilename());
+ OptArgs.push_back(Args.MakeArgString(llvm::Twine("-O") + OOpt));
+ OptArgs.push_back("-o");
+ OptArgs.push_back(Output.getFilename());
C.addCommand(std::make_unique<Command>(
- JA, *this, ResponseFileSupport::AtFileCurCP(), WasmOpt, CmdArgs,
+ JA, *this, ResponseFileSupport::AtFileCurCP(), WasmOpt, OptArgs,
Inputs, Output));
}
}
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