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fix(compiler/rustc_target): set correct linker flags for wasm32v1-none #145539

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fix(compiler/rustc_target): set correct linker flags for wasm32v1-none #145539

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fix(compiler/rustc_target): set correct linker flags for `wasm32v1-none`
StackOverflowExcept1on Aug 17, 2025
35f2feb
use `--mllvm=-mcpu=mvp`
StackOverflowExcept1on Aug 17, 2025
8f0ff59
add `--mllvm=-mattr=+mutable-globals`
StackOverflowExcept1on Aug 18, 2025
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7 changes: 6 additions & 1 deletion compiler/rustc_target/src/spec/targets/wasm32v1_none.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,11 @@ pub(crate) fn target() -> Target {
// For now this target just never has an entry symbol no matter the output
// type, so unconditionally pass this.
"--no-entry",
// It is also necessary to explicitly set CPU and features since some changes
// were made to WebAssembly starting with LLVM 20.1.0:
// https://releases.llvm.org/20.1.0/docs/ReleaseNotes.html#changes-to-the-webassembly-backend
"--mllvm=-mcpu=mvp",
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Doing it at the place I indicated (the WasmLd implementation) has the advantage that it works for all wasm targets and also when the user passes -Ctarget-cpu to override the target default.

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Yes, that's probably good idea, but we need WasmTM->CPU to be set from the command line.

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@bjorn3 bjorn3 Aug 17, 2025 •
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wasm-ld can't notice any difference between setting this cli arg in the target spec and setting it in the WasmLd implementation I linked to.

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Yes, you're right. I checked in the debugger and it's also worth adding --mllvm=-mattr=+mutable-globals to change WasmTM->TargetFS (features set).

"--mllvm=-mattr=+mutable-globals",
],
);
options.add_pre_link_args(
Expand All @@ -37,7 +42,7 @@ pub(crate) fn target() -> Target {
// Make sure clang uses LLD as its linker and is configured appropriately
// otherwise
"--target=wasm32-unknown-unknown",
"-Wl,--no-entry",
"-Wl,--no-entry,--mllvm=-mcpu=mvp,--mllvm=-mattr=+mutable-globals",
],
);

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