Apply the sbrk/brk value at compile time #2366
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tlively
reviewed
Sep 30, 2019
src/passes/PostEmscripten.cpp
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| @@ -80,6 +81,23 @@ struct PostEmscripten : public Pass { | |||
| func->body = builder.makeConst(Literal(int32_t(sbrkPtr))); | |||
| func->module = func->base = Name(); | |||
| } | |||
| // Apply the sbrk ptr value, if it was provided. | |||
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It would be good if this comment explained what it means to apply the sbrk ptr value. I'm still not sure why the value needs to be written into memory.
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Sure, added more text there now.
tlively
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Sep 30, 2019
kripken
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Oct 2, 2019
Emscripten side of WebAssembly/binaryen#2366 (that must roll first), this tells binaryen to set the value in the wasm binary, which fixes standalone wasm module's sbrk() usage (as normally we set this is JS). This also disables eval-ctors for the wasm backend, see #9527 , which made an incorrect assumption about the sbrk initial location - JS may modify it during startup, so we can't assume it's constant. This affects only -Oz so it's probably not many users. After this PR we should be correct in both standalone and non-standalone modes, and later we can look into re-enabling eval-ctors.
belraquib
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Dec 23, 2020
Emscripten side of WebAssembly/binaryen#2366 (that must roll first), this tells binaryen to set the value in the wasm binary, which fixes standalone wasm module's sbrk() usage (as normally we set this is JS). This also disables eval-ctors for the wasm backend, see emscripten-core#9527 , which made an incorrect assumption about the sbrk initial location - JS may modify it during startup, so we can't assume it's constant. This affects only -Oz so it's probably not many users. After this PR we should be correct in both standalone and non-standalone modes, and later we can look into re-enabling eval-ctors.
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We've had an option to set the location of the sbrk ptr, but not the value. Applying the value as well is necessary for standalone wasm, as otherwise we set it in JS.