Don't change WASM_EXCEPTIONS mode when setting -fno-exceptions#26184
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dschuff merged 1 commit intoemscripten-core:mainfrom Jan 28, 2026
Merged
Don't change WASM_EXCEPTIONS mode when setting -fno-exceptions#26184dschuff merged 1 commit intoemscripten-core:mainfrom
dschuff merged 1 commit intoemscripten-core:mainfrom
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We have 3 main user-facing EH flags, `-fwasm-exceptions`, `-fexceptions`, and `-fno-exceptions`. IIRC they aren't supposed to be mutually exclusive, -fwasm-exceptions` composes with the other 2, setting the mode of codegen, where the other 2 set whether exceptions compile. If you do `em++ -fno-exceptions -fwasm-exceptions` on a file that has try/catch, you get the expected compile-time error. However if you do `em++ -fwasm-exceptions -fno-exceptions` you should get the same error, but instead you get `clang++: error: invalid argument '-fwasm-exceptions' not allowed with '-enable-emscripten-sjlj'`. This is because the underlying clang is indeed getting passed the `-mllvm -enable-emscripten-sjlj` flag in the latter case but not the former case.
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I think this is an OK solution? aside from the effect tested for here, it will affect the error checking for combinations with settings like DISABLE_EXCEPTION_CATCHING, but I think not in a way that should break things? |
aheejin
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Jan 28, 2026
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I can't figure out why the error changes from the top of my head, but -fno-exceptions changing the exception kind is certainly weird to me.
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We have 3 main user-facing EH flags,
-fwasm-exceptions,-fexceptions,and
-fno-exceptions. IIRC they aren't supposed to be mutually exclusive,-fwasm-exceptions` composes with the other 2, setting the mode of codegen,
where the other 2 set whether exceptions compile.
If you do
em++ -fno-exceptions -fwasm-exceptionson a file that has try/catch,you get the expected compile-time error. However if you do
em++ -fwasm-exceptions -fno-exceptionsyou should get the same error, butinstead you get
clang++: error: invalid argument '-fwasm-exceptions' not allowed with '-enable-emscripten-sjlj'.This is because the underlying clang is indeed getting passed the
-mllvm -enable-emscripten-sjljflag in the latter case but not the former case.