Revert "Make JS exception catching code conditional. NFC (#22380)" (#22426)

This reverts commit eb4d36d.

The change caused a regression when building some parts of the llvm
testsuite.

In particular, when code is linked that was build with -fexceptions, but
-fexceptions was not given at link time.

In addition to the revered change I also had to move
`__cxa_get_exception_ptr` to `private_typeinfo.cpp`. This was converted
to native function in #22421, but, when combined with this change/revert
it also needs to be available in the `-noexcept` version of libc++abi.
See the comment in `private_typeinfo.cpp`

Author: sbc100

.circleci/config.yml

@@ -543,7 +543,6 @@ jobs:
           test_targets: "
             lto2.test_dylink_syslibs_all
             lto2.test_float_builtins
-            lto2.test_emscripten_lazy_load_code_unconditional
             lto0.test_exceptions_allowed_uncaught
             lto0.test_longjmp_standalone_standalone
             lto0.test_embind_i64_val

src/library_exceptions.js

@@ -125,7 +125,6 @@ var LibraryExceptions = {
 
   llvm_eh_typeid_for: (type) => type,
 
-#if !DISABLE_EXCEPTION_CATCHING
   __cxa_begin_catch__deps: ['$exceptionCaught', '__cxa_increment_exception_refcount',
                             '__cxa_get_exception_ptr',
                             '$uncaughtExceptionCount'],
@@ -257,17 +256,7 @@ var LibraryExceptions = {
     {{{ makeThrow('exceptionLast') }}}
   },
 
-  $incrementExceptionRefcount__deps: ['__cxa_increment_exception_refcount'],
-  $incrementExceptionRefcount: (ptr) => ___cxa_increment_exception_refcount(ptr),
-
-  $decrementExceptionRefcount__deps: ['__cxa_decrement_exception_refcount'],
-  $decrementExceptionRefcount: (ptr) => ___cxa_decrement_exception_refcount(ptr),
-
-  $getExceptionMessage__deps: ['$getExceptionMessageCommon'],
-  $getExceptionMessage: (ptr) => getExceptionMessageCommon(ptr),
-#endif // !DISABLE_EXCEPTION_CATCHING
-#endif // !WASM_EXCEPTIONS
-
+#endif
 #if WASM_EXCEPTIONS || !DISABLE_EXCEPTION_CATCHING
   $getExceptionMessageCommon__deps: ['__get_exception_message', 'free', '$stackSave', '$stackRestore', '$stackAlloc'],
   $getExceptionMessageCommon: (ptr) => {
@@ -342,23 +331,19 @@ var LibraryExceptions = {
     var ptr = getCppExceptionThrownObjectFromWebAssemblyException(ex);
     return getExceptionMessageCommon(ptr);
   },
-#endif // WASM_EXCEPTIONS
-};
 
-function addStub(name) {
-  LibraryManager.library[name] = function() { abort(); };
-  LibraryManager.library[`${name}__sig`] = '';
-#if !INCLUDE_FULL_LIBRARY
-  LibraryManager.library[`${name}__deps`] = [function() {
-    error(`DISABLE_EXCEPTION_CATCHING was set, which means no C++ exception catching support code is linked in, but such support is required by symbol '${name}'. Either set DISABLE_EXCEPTION_CATCHING=0 (if you do want exception catching) or compile all source files with DISABLE_EXCEPTION_CATCHING=1.`);
-  }];
-#endif
-}
+#elif !DISABLE_EXCEPTION_CATCHING
+  $incrementExceptionRefcount__deps: ['__cxa_increment_exception_refcount'],
+  $incrementExceptionRefcount: (ptr) => ___cxa_increment_exception_refcount(ptr),
+
+  $decrementExceptionRefcount__deps: ['__cxa_decrement_exception_refcount'],
+  $decrementExceptionRefcount: (ptr) => ___cxa_decrement_exception_refcount(ptr),
+
+  $getExceptionMessage__deps: ['$getExceptionMessageCommon'],
+  $getExceptionMessage: (ptr) => getExceptionMessageCommon(ptr),
 
-#if DISABLE_EXCEPTION_CATCHING
-addStub('__cxa_begin_catch');
-addStub('__cxa_end_catch');
 #endif
+};
 
 #if !WASM_EXCEPTIONS
 // In LLVM, exceptions generate a set of functions of form
@@ -367,9 +352,6 @@ addStub('__cxa_end_catch');
 // a single function '__cxa_find_matching_catch' that variadically processes all
 // of these functions using JS 'arguments' object.
 addCxaCatch = (n) => {
-#if DISABLE_EXCEPTION_CATCHING
-  addStub(`__cxa_find_matching_catch_${n}`);
-#else
   const args = [];
   // Confusingly, the actual number of asrgument is n - 2. According to the llvm
   // code in WebAssemblyLowerEmscriptenEHSjLj.cpp:
@@ -386,7 +368,6 @@ addCxaCatch = (n) => {
   LibraryManager.library[`__cxa_find_matching_catch_${n}__sig`] = sig;
   LibraryManager.library[`__cxa_find_matching_catch_${n}__deps`] = ['$findMatchingCatch'];
   LibraryManager.library[`__cxa_find_matching_catch_${n}`] = eval(`(${args}) => findMatchingCatch([${argString}])`);
-#endif
 };
 
 // Add the first 2-5 catch handlers preemptively.  Others get added on demand in

system/lib/libcxxabi/src/cxa_exception_emscripten.cpp

@@ -114,26 +114,6 @@ void __cxa_free_exception(void *thrown_object) throw() {
     __aligned_free_with_fallback((void *)raw_buffer);
 }
 
-void *__cxa_get_exception_ptr(void *thrown_object) throw() {
-    // Get pointer which is expected to be received by catch clause in C++ code.
-    // It may be adjusted when the pointer is casted to some of the exception
-    // object base classes (e.g. when virtual inheritance is used). When a pointer
-    // is thrown this method should return the thrown pointer itself.
-    // Work around a fastcomp bug, this code is still included for some reason in
-    // a build without exceptions support.
-    __cxa_exception* ex = cxa_exception_from_thrown_object(thrown_object);
-    bool is_pointer = !!dynamic_cast<__pointer_type_info*>(ex->exceptionType);
-    void* rtn;
-    if (is_pointer)
-        rtn = *(void**)thrown_object;
-    else if (ex->adjustedPtr)
-        rtn = ex->adjustedPtr;
-    else
-        rtn = ex;
-    DEBUG("__cxa_get_exception_ptr %p -> %p\n", thrown_object, rtn);
-    return rtn;
-}
-
 /*
     If thrown_object is not null, atomically increment the referenceCount field
     of the __cxa_exception header associated with the thrown object referred to

system/lib/libcxxabi/src/private_typeinfo.cpp

@@ -1530,11 +1530,17 @@ __base_class_type_info::search_below_dst(__dynamic_cast_info* info,
                                       not_public_path,
                                   use_strcmp);
 }
+}  // __cxxabiv1
 
-// XXX EMSCRIPTEN
 
+// XXX EMSCRIPTEN
 #ifndef __WASM_EXCEPTIONS__
 
+#include "cxa_exception.h"
+
+namespace __cxxabiv1
+{
+
 // These functions are used by the emscripten-style exception handling
 // mechanism.
 // Note that they need to be included even in the `-noexcept` build of
@@ -1555,7 +1561,33 @@ int __cxa_can_catch(__shim_type_info* catchType, __shim_type_info* excpType, voi
   return ret;
 }
 
+static
+inline
+__cxa_exception*
+cxa_exception_from_thrown_object(void* thrown_object)
+{
+    return static_cast<__cxa_exception*>(thrown_object) - 1;
+}
+
+void *__cxa_get_exception_ptr(void *thrown_object) throw() {
+    // Get pointer which is expected to be received by catch clause in C++ code.
+    // It may be adjusted when the pointer is casted to some of the exception
+    // object base classes (e.g. when virtual inheritance is used). When a pointer
+    // is thrown this method should return the thrown pointer itself.
+    // Work around a fastcomp bug, this code is still included for some reason in
+    // a build without exceptions support.
+    __cxa_exception* ex = cxa_exception_from_thrown_object(thrown_object);
+    bool is_pointer = !!dynamic_cast<__pointer_type_info*>(ex->exceptionType);
+    if (is_pointer)
+        return *(void**)thrown_object;
+    if (ex->adjustedPtr)
+        return ex->adjustedPtr;
+    return ex;
+}
+
 }
-#endif // __EMSCRIPTEN_EXCEPTIONS__
 
 }  // __cxxabiv1
+
+#endif // !__WASM_EXCEPTIONS__
+

test/other/metadce/test_metadce_cxx_lto.exports

@@ -1,3 +1,4 @@
+__cxa_increment_exception_refcount
 __indirect_function_table
 __wasm_call_ctors
 _emscripten_stack_alloc

test/other/metadce/test_metadce_cxx_lto.size

@@ -1 +1 @@
-128959
+129045

test/test_other.py

@@ -11590,12 +11590,12 @@ def test_fignore_exceptions(self):
     # enabling exceptions at link and compile works
     'on': (['-fexceptions'], ['-fexceptions'], True),
     # just compile isn't enough as the JS runtime lacks support
-    'compile_only': (['-fexceptions'], [], False, True),
+    'compile_only': (['-fexceptions'], [], False),
     # just link isn't enough as codegen didn't emit exceptions support
     'link_only': ([], ['-fexceptions'], False),
     'standalone': (['-fexceptions'], ['-fexceptions', '-sSTANDALONE_WASM', '-sWASM_BIGINT'], True),
   })
-  def test_f_exception(self, compile_flags, link_flags, expect_caught, expect_link_failure=False):
+  def test_f_exception(self, compile_flags, link_flags, expect_caught):
     create_file('src.cpp', r'''
       #include <stdio.h>
       int main () {
@@ -11608,11 +11608,6 @@ def test_f_exception(self, compile_flags, link_flags, expect_caught, expect_link
       }
     ''')
     self.run_process([EMXX, 'src.cpp', '-c', '-o', 'src.o'] + compile_flags)
-    if expect_link_failure:
-      err = self.expect_fail([EMXX, 'src.o'] + link_flags)
-      self.assertContained("error: DISABLE_EXCEPTION_CATCHING was set, which means no C++ exception catching support code is linked in, but such support is required by symbol '__cxa_begin_catch'", err)
-      return
-
     self.run_process([EMXX, 'src.o'] + link_flags)
     result = self.run_js('a.out.js', assert_returncode=0 if expect_caught else NON_ZERO)
     if not expect_caught:

tools/maint/gen_sig_info.py

@@ -295,7 +295,6 @@ def extract_sig_info(sig_info, extra_settings=None, extra_cflags=None, cxx=False
     # Enable as many settings as we can here to ensure the maximum number
     # of JS symbols are included.
     'STACK_OVERFLOW_CHECK': 1,
-    'DISABLE_EXCEPTION_CATCHING': 0,
     'USE_SDL': 1,
     'USE_GLFW': 0,
     'FETCH': 1,