Fix initial value of sbrk(0) #9553
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tlively
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Oct 2, 2019
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The sbrk pointer is basically the location in memory where we store the program brk. We normally set it up in JS, as we allow JS to allocate during startup. Then when wasm runs it continues with that value. But in standalone mode, there is no JS, so we use the new binaryen flag to hardcode it in the wasm binary. That interaction between JS and wasm is also why the ctor evaller is not valid; JS can modify the value but the ctor evaller assumes what it sees in memory is what will be there at runtime. |
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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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
-Ozso 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.