From a866e7a6c93e2d8bd3612f0fde572bb3670cde05 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Fri, 8 Mar 2024 09:58:58 -0800
Subject: [PATCH] Fix for longjmp(.., 0) under wasm EH

Fixes: #21486
---
 system/lib/compiler-rt/emscripten_setjmp.c |  8 +++++++
 test/core/test_longjmp_zero.c              | 28 ++++++++++++++++++++++
 test/core/test_longjmp_zero.out            |  3 +++
 test/test_core.py                          |  4 ++++
 4 files changed, 43 insertions(+)
 create mode 100644 test/core/test_longjmp_zero.c
 create mode 100644 test/core/test_longjmp_zero.out

diff --git a/system/lib/compiler-rt/emscripten_setjmp.c b/system/lib/compiler-rt/emscripten_setjmp.c
index 8dd944b010b5..ae68acb08380 100644
--- a/system/lib/compiler-rt/emscripten_setjmp.c
+++ b/system/lib/compiler-rt/emscripten_setjmp.c
@@ -90,6 +90,14 @@ thread_local struct __WasmLongjmpArgs __wasm_longjmp_args;
 // TODO Consider switching to throwing two values at the same time later.
 void __wasm_longjmp(void *env, int val) {
   __wasm_longjmp_args.env = env;
+  /*
+  * C standard:
+  *   The longjmp function cannot cause the setjmp macro to return
+  *   the value 0; if val is 0, the setjmp macro returns the value 1.
+  */
+  if (val == 0) {
+    val = 1;
+  }
   __wasm_longjmp_args.val = val;
   __builtin_wasm_throw(C_LONGJMP, &__wasm_longjmp_args);
 }
diff --git a/test/core/test_longjmp_zero.c b/test/core/test_longjmp_zero.c
new file mode 100644
index 000000000000..dea87ef64d52
--- /dev/null
+++ b/test/core/test_longjmp_zero.c
@@ -0,0 +1,28 @@
+/*
+ * Copyright 2016 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <stdio.h>
+#include <setjmp.h>
+
+int main() {
+  printf("start\n");
+  jmp_buf b1;
+  int val = setjmp(b1);
+  if (val) {
+    printf("success\n");
+    return 0;
+  }
+  /*
+   * C standard:
+   * > The longjmp function cannot cause the setjmp macro to return
+   * > the value 0; if val is 0, the setjmp macro returns the value 1.
+   */
+  printf("longjmp\n");
+  longjmp(b1, 0);
+  __builtin_trap();
+  return 0;
+}
diff --git a/test/core/test_longjmp_zero.out b/test/core/test_longjmp_zero.out
new file mode 100644
index 000000000000..8beb03149936
--- /dev/null
+++ b/test/core/test_longjmp_zero.out
@@ -0,0 +1,3 @@
+start
+longjmp
+success
diff --git a/test/test_core.py b/test/test_core.py
index e9d817812ee9..2622dd04f39f 100644
--- a/test/test_core.py
+++ b/test/test_core.py
@@ -892,6 +892,10 @@ def test_longjmp_standalone(self):
   def test_longjmp(self):
     self.do_core_test('test_longjmp.c')
 
+  @with_both_sjlj
+  def test_longjmp_zero(self):
+    self.do_core_test('test_longjmp_zero.c')
+
   def test_longjmp_with_and_without_exceptions(self):
     # Emscripten SjLj with and without Emscripten EH support
     self.set_setting('SUPPORT_LONGJMP', 'emscripten')