[EH] Make Wasm EH rethrow print stack traces (#20372)

In Wasm EH, even if we set `-sASSERTION` or `-sEXCEPTION_STACK_TRACES`,
if we rethrow an exception in the code, we lose the effect of that
option because previously we called `__throw_exception_with_stack_trace`
only in `__cxa_throw`:
https://github.com/emscripten-core/emscripten/blob/9ce7020632aa6f7578c6e40e197b800a4dd7073f/system/lib/libcxxabi/src/cxa_exception.cpp#L294-L296

This adds the same mechanism to `__cxa_rethrow` (which is used for
C++ `throw;`) and `__cxa_rethrow_primary_exception` (which is used for
`std::rethrow_exception`).

This does not solve the problem of losing stack traces _before_ the
rethrowing. libc++abi's `__cxa_rethrow` and
`__cxa_rethrow_primary_exception` are implemented as throwing a pointer
in the same way we first throw it and they are not aware of any
metadata. This happens even in the native platform with GDB; GDB's
backtrace only shows stack traces after rethrowing. We may try to fix
this later by passing `exnref`
(WebAssembly/exception-handling#281) to the
library, but this is likely to take some time.

Partially fixes #20301.

system/lib/libcxxabi/src/cxa_exception.cpp

@@ -287,14 +287,10 @@ __cxa_throw(void *thrown_object, std::type_info *tinfo, void (_LIBCXXABI_DTOR_FU
 
 #ifdef __USING_SJLJ_EXCEPTIONS__
     _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
-#elif __USING_WASM_EXCEPTIONS__
-#ifdef NDEBUG
-    _Unwind_RaiseException(&exception_header->unwindHeader);
-#else
+#elif defined(__USING_WASM_EXCEPTIONS__) && !defined(NDEBUG)
     // In debug mode, call a JS library function to use WebAssembly.Exception JS
     // API, which enables us to include stack traces
     __throw_exception_with_stack_trace(&exception_header->unwindHeader);
-#endif
 #else
     _Unwind_RaiseException(&exception_header->unwindHeader);
 #endif
@@ -644,6 +640,10 @@ void __cxa_rethrow() {
     }
 #ifdef __USING_SJLJ_EXCEPTIONS__
     _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
+#elif defined(__USING_WASM_EXCEPTIONS__) && !defined(NDEBUG)
+    // In debug mode, call a JS library function to use WebAssembly.Exception JS
+    // API, which enables us to include stack traces
+    __throw_exception_with_stack_trace(&exception_header->unwindHeader);
 #else
     _Unwind_RaiseException(&exception_header->unwindHeader);
 #endif
@@ -769,8 +769,13 @@ __cxa_rethrow_primary_exception(void* thrown_object)
         dep_exception_header->unwindHeader.exception_cleanup = dependent_exception_cleanup;
 #ifdef __USING_SJLJ_EXCEPTIONS__
         _Unwind_SjLj_RaiseException(&dep_exception_header->unwindHeader);
+#elif defined(__USING_WASM_EXCEPTIONS__) && !defined(NDEBUG)
+        // In debug mode, call a JS library function to use
+        // WebAssembly.Exception JS API, which enables us to include stack
+        // traces
+        __throw_exception_with_stack_trace(&exception_header->unwindHeader);
 #else
-        _Unwind_RaiseException(&dep_exception_header->unwindHeader);
+        _Unwind_RaiseException(&exception_header->unwindHeader);
 #endif
         // Some sort of unwinding error.  Note that terminate is a handler.
         __cxa_begin_catch(&dep_exception_header->unwindHeader);

test/test_other.py

@@ -8529,7 +8529,7 @@ def test_exceptions_stack_trace_and_message(self, wasm_eh):
         return 0;
       }
     '''
-    emcc_args = ['-g']
+    self.emcc_args = ['-g']
 
     # Stack trace and message example for this example code:
     # exiting due to exception: [object WebAssembly.Exception],Error: std::runtime_error,my message
@@ -8557,9 +8557,9 @@ def test_exceptions_stack_trace_and_message(self, wasm_eh):
       # self.require_wasm_eh() if this issue is fixed later.
       self.require_v8()
 
-      emcc_args += ['-fwasm-exceptions']
+      self.emcc_args += ['-fwasm-exceptions']
     else:
-      emcc_args += ['-fexceptions']
+      self.emcc_args += ['-fexceptions']
 
     # Stack traces are enabled when either of ASSERTIONS or
     # EXCEPTION_STACK_TRACES is enabled. You can't disable
@@ -8568,16 +8568,14 @@ def test_exceptions_stack_trace_and_message(self, wasm_eh):
     # Prints stack traces
     self.set_setting('ASSERTIONS', 1)
     self.set_setting('EXCEPTION_STACK_TRACES', 1)
-    self.do_run(src, emcc_args=emcc_args, assert_all=True,
-                assert_returncode=NON_ZERO, expected_output=stack_trace_checks,
-                regex=True)
+    self.do_run(src, assert_all=True, assert_returncode=NON_ZERO,
+                expected_output=stack_trace_checks, regex=True)
 
     # Prints stack traces
     self.set_setting('ASSERTIONS', 0)
     self.set_setting('EXCEPTION_STACK_TRACES', 1)
-    self.do_run(src, emcc_args=emcc_args, assert_all=True,
-                assert_returncode=NON_ZERO, expected_output=stack_trace_checks,
-                regex=True)
+    self.do_run(src, assert_all=True, assert_returncode=NON_ZERO,
+                expected_output=stack_trace_checks, regex=True)
 
     # Not allowed
     self.set_setting('ASSERTIONS', 1)
@@ -8589,10 +8587,82 @@ def test_exceptions_stack_trace_and_message(self, wasm_eh):
     # Doesn't print stack traces
     self.set_setting('ASSERTIONS', 0)
     self.set_setting('EXCEPTION_STACK_TRACES', 0)
-    err = self.do_run(src, emcc_args=emcc_args, assert_returncode=NON_ZERO)
+    err = self.do_run(src, assert_returncode=NON_ZERO)
     for check in stack_trace_checks:
       self.assertFalse(re.search(check, err), 'Expected regex "%s" to not match on:\n%s' % (check, err))
 
+  @parameterized({
+    '': (False,),
+    'wasm': (True,),
+  })
+  def test_exceptions_rethrow_stack_trace_and_message(self, wasm_eh):
+    self.emcc_args = ['-g']
+    if wasm_eh:
+      # FIXME Node v18.13 (LTS as of Jan 2023) has not yet implemented the new
+      # optional 'traceStack' option in WebAssembly.Exception constructor
+      # (https://developer.mozilla.org/en-US/docs/WebAssembly/JavaScript_interface/Exception/Exception)
+      # and embeds stack traces unconditionally. Change this back to
+      # self.require_wasm_eh() if this issue is fixed later.
+      self.require_v8()
+      self.emcc_args += ['-fwasm-exceptions']
+    else:
+      self.emcc_args += ['-fexceptions']
+
+    # Rethrowing exception currently loses the stack trace before the rethrowing
+    # due to how rethrowing is implemented. So in the examples below we don't
+    # print 'bar' at the moment.
+    # TODO Make rethrow preserve stack traces before rethrowing?
+    rethrow_src1 = r'''
+      #include <stdexcept>
+
+      void bar() {
+        throw std::runtime_error("my message");
+      }
+      void foo() {
+        try {
+          bar();
+        } catch (...) {
+          throw; // rethrowing by throw;
+        }
+      }
+      int main() {
+        foo();
+        return 0;
+      }
+    '''
+    rethrow_src2 = r'''
+      #include <stdexcept>
+
+      void bar() {
+        throw std::runtime_error("my message");
+      }
+      void foo() {
+        try {
+          bar();
+        } catch (...) {
+          auto e = std::current_exception();
+          std::rethrow_exception(e); // rethrowing by std::rethrow_exception
+        }
+      }
+      int main() {
+        foo();
+        return 0;
+      }
+    '''
+    rethrow_stack_trace_checks = [
+      'std::runtime_error[:,][ ]?my message',  # 'std::runtime_error: my message' for Emscripten EH
+      'at ((src.wasm.)?_?__cxa_rethrow|___resumeException)',  # '___resumeException' (JS symbol) for Emscripten EH
+      'at (src.wasm.)?foo',
+      'at (src.wasm.)?main']
+
+    self.set_setting('ASSERTIONS', 1)
+    err = self.do_run(rethrow_src1, assert_all=True, assert_returncode=NON_ZERO,
+                      expected_output=rethrow_stack_trace_checks, regex=True)
+    self.assertNotContained('bar', err)
+    err = self.do_run(rethrow_src2, assert_all=True, assert_returncode=NON_ZERO,
+                      expected_output=rethrow_stack_trace_checks, regex=True)
+    self.assertNotContained('bar', err)
+
   @requires_node
   def test_jsrun(self):
     print(config.NODE_JS)