Add a setjmp/longjmp runtime for a new sjlj translation proposed in LLVM (#21502)

the new runtime code is basically a copy from:
https://github.com/yamt/garbage/blob/wasm-sjlj-alt2/wasm/longjmp/rt.c.

The corresponding LLVM change:
llvm/llvm-project#84137

Discussion:
https://docs.google.com/document/d/1ZvTPT36K5jjiedF8MCXbEmYjULJjI723aOAks1IdLLg/edit

Author: yamt

AUTHORS

@@ -597,3 +597,4 @@ a license to everyone to use it as detailed in LICENSE.)
 * James Hu <jameshu2022@gmail.com>
 * Jerry Zhuang <jerry.zhuang@jwzg.com>
 * Taisei Kon <kinsei0916@gmail.com>
+* YAMAMOTO Takashi <yamamoto@midokura.com>

system/lib/compiler-rt/emscripten_setjmp.c

@@ -5,6 +5,7 @@
 * found in the LICENSE file.
 */
 
+#include <assert.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <setjmp.h>
@@ -79,33 +80,59 @@ void emscripten_longjmp(uintptr_t env, int val) {
 #endif
 
 #ifdef __USING_WASM_SJLJ__
-
 struct __WasmLongjmpArgs {
   void *env;
   int val;
 };
 
-thread_local struct __WasmLongjmpArgs __wasm_longjmp_args;
-
 // llvm uses `1` for the __c_longjmp tag.
 // See https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/CodeGen/WasmEHFuncInfo.h
 #define C_LONGJMP 1
+#endif
+
+// jmp_buf should have large enough size and alignment to contain
+// this structure.
+struct jmp_buf_impl {
+  void* func_invocation_id;
+  uint32_t label;
+#ifdef __USING_WASM_SJLJ__
+  struct __WasmLongjmpArgs arg;
+#endif
+};
 
+void __wasm_setjmp(void* env, uint32_t label, void* func_invocation_id) {
+  struct jmp_buf_impl* jb = env;
+  assert(label != 0);                 // ABI contract
+  assert(func_invocation_id != NULL); // sanity check
+  jb->func_invocation_id = func_invocation_id;
+  jb->label = label;
+}
+
+uint32_t __wasm_setjmp_test(void* env, void* func_invocation_id) {
+  struct jmp_buf_impl* jb = env;
+  assert(jb->label != 0);             // ABI contract
+  assert(func_invocation_id != NULL); // sanity check
+  if (jb->func_invocation_id == func_invocation_id) {
+    return jb->label;
+  }
+  return 0;
+}
+
+#ifdef __USING_WASM_SJLJ__
 // Wasm EH allows us to throw and catch multiple values, but that requires
 // multivalue support in the toolchain, whch is not reliable at the time.
 // 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.
-  */
+void __wasm_longjmp(void* env, int val) {
+  struct jmp_buf_impl* jb = env;
+  struct __WasmLongjmpArgs* arg = &jb->arg;
+  // C standard says:
+  // 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);
+  arg->env = env;
+  arg->val = val;
+  __builtin_wasm_throw(C_LONGJMP, arg);
 }
-
 #endif