Configure a new stack in cabi_realloc - #854
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alexcrichton merged 1 commit intoJul 27, 2026
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Wrong button... |
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Oh right, I should also mention that I've updated the implementation of |
This commit is an update to the `cabi_realloc` export configured by wasi-libc, specifically for wasip3 targets. The change here is to change the entrypoint from a C function to a small assembly wrapper which configures the stack pointer and TLS base before calling into C. This is to account for the spec change in WebAssembly/component-model#680 where `realloc` hooks are now going to be invoked with context slots set to 0. This means that `cabi_realloc` runs with no stack, and this would quickly abort in wasi-libc otherwise. The change here is to, when the ABI is using `context` slots for the stack pointer, have an assembly wrapper that configures a known-good stack and TLS block for `cabi_realloc` to use. Once configured the normal C-based `cabi_realloc` routine runs. This is tested against bytecodealliance/wasmtime#13949 to ensure it works on the p3 target with/without coop threading and before/after that Wasmtime change.
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| @@ -0,0 +1,21 @@ | |||
| // This is a "surgical" augmentation for the generated `wasip{2,3}.c` files in | |||
| // wasi-libc which changes the behavior of the generated `cabi_realloc`. Ideally | |||
| // `wit-bindgen` would have a mode that doesn't generate `cabi_realloc`, but that | |||
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Is there an issue for this? It would be nice to remove the need for this "surgery" sooner rather than later.
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Not currently, no
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This commit is an update to the
cabi_reallocexport configured by wasi-libc, specifically for wasip3 targets. The change here is to change the entrypoint from a C function to a small assembly wrapper which configures the stack pointer and TLS base before calling into C. This is to account for the spec change in WebAssembly/component-model#680 wherereallochooks are now going to be invoked with context slots set to 0. This means thatcabi_reallocruns with no stack, and this would quickly abort in wasi-libc otherwise.The change here is to, when the ABI is using
contextslots for the stack pointer, have an assembly wrapper that configures a known-good stack and TLS block forcabi_reallocto use. Once configured the normal C-basedcabi_reallocroutine runs. This is tested against bytecodealliance/wasmtime#13949 to ensure it works on the p3 target with/without coop threading and before/after that Wasmtime change.