[wasm2c] Fix exception testing on macOS (#2716)

This commit addresses the assertion failures during exception testing
in `wasm2c` on macOS:
`Assertion failed: (!(ss.ss_flags & SS_ONSTACK) && "attempt to
deallocate altstack while in use")`

Exception handling in wasm2c uses `wasm_rt_try(target)` which mapped
to `sigsetjmp(buf, 1)`. However, on macOS (XNU), performing nested
`sigsetjmp(..., 1)` and `siglongjmp` across threads with an allocated
alternate signal stack can erroneously cause the kernel to preserve the
`SS_ONSTACK` flag in the thread state, even when the exception did not
originate from the signal handler.

Since WebAssembly exception handling relies strictly on
`setjmp`/`longjmp`
for control flow and does not need to restore signal masks (unlike stack
exhaustion traps, which do need the mask to unblock `SIGSEGV`), the fix
is to simply avoid saving the signal mask for exception boundaries.

We split `WASM_RT_SETJMP_SETBUF` into two variants:
- `WASM_RT_SETJMP_TRAP_SETBUF`: Uses `sigsetjmp(buf, 1)` for traps
(safely handles `SIGSEGV`).
- `WASM_RT_SETJMP_EXN_SETBUF`: Uses `sigsetjmp(buf, 0)` for Wasm
exceptions (bypasses `SS_ONSTACK` bug).

This also reverts commit 74cc83c
(which temporarily disabled `macos-latest` in CI), as the tests now
pass successfully.

Fixes #2654

Author: kevmoo

.github/workflows/build.yml

@@ -30,9 +30,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        # Temporarily replaced macos-latest with macos-14.
-        # See https://github.com/WebAssembly/wabt/issues/2654
-        os: [ubuntu-latest, macos-14, windows-latest]
+        os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
     - uses: actions/setup-python@v5
       with:
@@ -45,7 +43,7 @@ jobs:
       if: matrix.os == 'ubuntu-latest'
     - name: install ninja (osx)
       run: brew install ninja
-      if: startsWith(matrix.os, 'macos-')
+      if: matrix.os == 'macos-latest'
     - name: install ninja (win)
       run: choco install ninja
       if: matrix.os == 'windows-latest'

wasm2c/wasm-rt.h

@@ -572,13 +572,27 @@ typedef struct {
 } wasm_rt_jmp_buf;
 
 #ifndef _WIN32
-#define WASM_RT_SETJMP_SETBUF(buf) sigsetjmp(buf, 1)
+#define WASM_RT_SETJMP_TRAP_SETBUF(buf) sigsetjmp(buf, 1)
+
+/**
+ * On macOS XNU, there is a bug where nested `sigsetjmp` and `siglongjmp` 
+ * across threads that have an allocated alternate signal stack (`SS_ONSTACK`) 
+ * will erroneously cause the kernel to preserve the `SS_ONSTACK` flag in the 
+ * thread state
+ *
+ * See: https://github.com/WebAssembly/wabt/issues/2654
+ * See: https://github.com/golang/go/issues/44501
+ */
+#define WASM_RT_SETJMP_EXN_SETBUF(buf) sigsetjmp(buf, 0)
 #else
-#define WASM_RT_SETJMP_SETBUF(buf) setjmp(buf)
+#define WASM_RT_SETJMP_TRAP_SETBUF(buf) setjmp(buf)
+#define WASM_RT_SETJMP_EXN_SETBUF(buf) setjmp(buf)
 #endif
 
 #define WASM_RT_SETJMP(buf) \
-  ((buf).initialized = true, WASM_RT_SETJMP_SETBUF((buf).buffer))
+  ((buf).initialized = true, WASM_RT_SETJMP_TRAP_SETBUF((buf).buffer))
+#define WASM_RT_SETJMP_EXN(buf) \
+  ((buf).initialized = true, WASM_RT_SETJMP_EXN_SETBUF((buf).buffer))
 
 #ifndef _WIN32
 #define WASM_RT_LONGJMP_UNCHECKED(buf, val) siglongjmp(buf, val)
@@ -604,7 +618,7 @@ WASM_RT_NO_RETURN void wasm_rt_trap(wasm_rt_trap_t);
 /** Return a human readable error string based on a trap type. */
 const char* wasm_rt_strerror(wasm_rt_trap_t trap);
 
-#define wasm_rt_try(target) WASM_RT_SETJMP(target)
+#define wasm_rt_try(target) WASM_RT_SETJMP_EXN(target)
 
 /** WebAssembly's default page size (64 KiB) */
 #define WASM_DEFAULT_PAGE_SIZE 65536