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Test out -D__USE_MINGW_SETJMP_NON_SEH #9929

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Jan 6, 2025
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Test out -D__USE_MINGW_SETJMP_NON_SEH #9929

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c988c09
Test out `-D__USE_MINGW_SETJMP_NON_SEH`
alexcrichton Jan 6, 2025
fc44313
Add a comment for the workaround
alexcrichton Jan 6, 2025
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8 changes: 8 additions & 0 deletions crates/wasmtime/build.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,14 @@ fn build_c_helpers() {
build.define("FEATURE_DEBUG_BUILTINS", None);
}

// On MinGW targets work around a bug in the MinGW compiler described at
// https://github.com/bytecodealliance/wasmtime/pull/9688#issuecomment-2573367719
if std::env::var("CARGO_CFG_WINDOWS").is_ok()
&& std::env::var("CARGO_CFG_TARGET_ENV").ok().as_deref() == Some("gnu")
{
build.define("__USE_MINGW_SETJMP_NON_SEH", None);
}

println!("cargo:rerun-if-changed=src/runtime/vm/helpers.c");
build.file("src/runtime/vm/helpers.c");
build.compile("wasmtime-helpers");
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60 changes: 5 additions & 55 deletions crates/wasmtime/src/runtime/vm/helpers.c
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Expand Up @@ -61,65 +61,15 @@ typedef sigjmp_buf platform_jmp_buf;
#define CONCAT(a, b) CONCAT2(a, b)
#define VERSIONED_SYMBOL(a) CONCAT(a, VERSIONED_SUFFIX)

// Define one function here, `wasmtime_setjmp_inverted`, which returns the
// negation of whether the call succeeded. Define then the actual import below
// of `wasmtime_setjmp_*` which returns the negation of this negation which
// means it returns whether the function invocation succeeded or not.
//
// Why in the world would we do this? For now: MinGW. In
// bytecodealliance/wasmtime#9675 that PR was originally failing CI only on
// MinGW and seems to be fixed by this. In that PR the signature of `body` here
// changed from a `void` return to a `bool` returned. That means that the body
// of this function changed from the historical:
//
// body(payload, callee);
// return 1;
//
// to what we actually want:
//
// return body(payload, callee);
//
// For some reason though this causes issues when unwinding via `longjmp` on
// Windows. Tests would exit with the error message:
//
// code 0xc0000028: An invalid or unaligned stack was encountered during an
// unwind operation. (os error 543)
//
// Debugging revealed that if this:
//
// return body(payload, callee);
//
// were written as:
//
// bool ret = body(payload, callee);
// return ret;
//
// then the bug would be "fixed". This "fix" didn't work in release mode
// however, leading to the current fix. For whatever reason it seems that
// unwinding is broken if there's not code between the `body(...)` indirect
// call and the function return. The `!` here below, inverting the return value,
// is the source of that "code".
//
// Ideally this `*_inverted` shim would go away and get past CI. It's unclear
// whether we're dealing with a miscompile in GCC, bad unwinding information
// generated by Cranelift for JIT code, or what. For now "this seems to work"
// but we'll also be in the process of forwarding this to some other Windows
// folks to see better what's going on.
static bool wasmtime_setjmp_inverted(void **buf_storage,
bool (*body)(void *, void *),
void *payload, void *callee) {
bool VERSIONED_SYMBOL(wasmtime_setjmp)(void **buf_storage,
bool (*body)(void *, void *),
void *payload, void *callee) {
platform_jmp_buf buf;
if (platform_setjmp(buf) != 0) {
return true;
return false;
}
*buf_storage = &buf;
return !body(payload, callee);
}

bool VERSIONED_SYMBOL(wasmtime_setjmp)(void **buf_storage,
bool (*body)(void *, void *),
void *payload, void *callee) {
return !wasmtime_setjmp_inverted(buf_storage, body, payload, callee);
return body(payload, callee);
}

void VERSIONED_SYMBOL(wasmtime_longjmp)(void *JmpBuf) {
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