Test out -D__USE_MINGW_SETJMP_NON_SEH (bytecodealliance#9929)

* Test out `-D__USE_MINGW_SETJMP_NON_SEH`

With respect to bytecodealliance#9688

prtest:full

* Add a comment for the workaround

Author: alexcrichton

crates/wasmtime/build.rs

@@ -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");

crates/wasmtime/src/runtime/vm/helpers.c

@@ -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) {