[EH] Apply Call EH personality fix from LLVM (emscripten-core#27445)

After llvm/llvm-project#209282, the user code
calls a personality function instead of `Unwind_CallPersonality`. It
also changed the signature of Wasm personality function. It had both
code generation and library changes, but now our waterfall picks up the
codegen changes but our libraries are still from the last release.

This applies llvm/llvm-project#209282 library
side patch here as well. This kind of change is rare enough so I don't
think we necessary should follow LLVM tot for libunwind, unless we
decide to do that broadly for all LLVM libraries.

Also this adds `system/lib/libunwind/include` to libcxx's `includes`
directory. Turns out so far we have been including Clang's default
`unwind.h` and it was OK but now we need to include the correct file.

This temporarily skips all Wasm EH tests to make the LLVM roll land.
They will be reenabled once the roll lands.

Fixes emscripten-core#27442.

Author: aheejin

system/lib/libcxxabi/src/cxa_personality.cpp

@@ -1021,9 +1021,7 @@ static inline void get_landing_pad(__cxa_catch_temp_type &dest,
 #endif
 }
 
-#ifdef __WASM_EXCEPTIONS__
-_Unwind_Reason_Code __gxx_personality_wasm0
-#elif defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)
+#if (defined(__SEH__) && !defined(__USING_SJLJ_EXCEPTIONS__)) || defined(__WASM_EXCEPTIONS__)
 static _Unwind_Reason_Code __gxx_personality_imp
 #else
 _LIBCXXABI_FUNC_VIS _Unwind_Reason_Code
@@ -1124,6 +1122,20 @@ __gxx_personality_seh0(PEXCEPTION_RECORD ms_exc, void *this_frame,
 }
 #endif
 
+#ifdef __WASM_EXCEPTIONS__
+extern "C" _LIBCXXABI_FUNC_VIS _Unwind_Reason_Code __gxx_wasm_personality_v0(void* exception_ptr) {
+  struct _Unwind_Exception* exception_object = (struct _Unwind_Exception*)exception_ptr;
+
+  // Reset the selector.
+  __wasm_lpad_context.selector = 0;
+
+  // Call personality function. Wasm does not have two-phase unwinding, so we
+  // only do the search phase.
+  return __gxx_personality_imp(1, _UA_SEARCH_PHASE, exception_object->exception_class, exception_object,
+                               (struct _Unwind_Context*)&__wasm_lpad_context);
+}
+#endif
+
 #else
 
 // Helper function to unwind one frame.

system/lib/libunwind/include/unwind.h

@@ -61,6 +61,10 @@ typedef struct _Unwind_Context _Unwind_Context;   // opaque
 #include <unwind_itanium.h>
 #endif
 
+#if defined(__WASM_EXCEPTIONS__)
+#include <unwind_wasm.h>
+#endif
+
 typedef _Unwind_Reason_Code (*_Unwind_Stop_Fn)
     (int version,
      _Unwind_Action actions,

system/lib/libunwind/include/unwind_wasm.h

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __WASM_UNWIND_H__
+#define __WASM_UNWIND_H__
+
+#include <threads.h>
+
+struct _Unwind_LandingPadContext {
+  // Input information to personality function
+  uintptr_t lpad_index; // landing pad index
+  uintptr_t lsda;       // LSDA address
+
+  // Output information computed by personality function
+  uintptr_t selector; // selector value
+};
+
+// Communication channel between compiler-generated user code and personality
+// function
+extern thread_local struct _Unwind_LandingPadContext __wasm_lpad_context;
+
+#endif // __WASM_UNWIND_H__

system/lib/libunwind/src/Unwind-wasm.c

@@ -19,46 +19,8 @@
 #include "unwind.h"
 #include <threads.h>
 
-_Unwind_Reason_Code __gxx_personality_wasm0(int version, _Unwind_Action actions,
-                                            uint64_t exceptionClass,
-                                            _Unwind_Exception *unwind_exception,
-                                            _Unwind_Context *context);
-
-struct _Unwind_LandingPadContext {
-  // Input information to personality function
-  uintptr_t lpad_index; // landing pad index
-  uintptr_t lsda;       // LSDA address
-
-  // Output information computed by personality function
-  uintptr_t selector; // selector value
-};
-
-// Communication channel between compiler-generated user code and personality
-// function
-thread_local struct _Unwind_LandingPadContext __wasm_lpad_context;
-
-/// Calls to this function are in landing pads in compiler-generated user code.
-/// In other EH schemes, stack unwinding is done by libunwind library, which
-/// calls the personality function for each frame it lands. On the other hand,
-/// WebAssembly stack unwinding process is performed by a VM, and the
-/// personality function cannot be called from there. So the compiler inserts a
-/// call to this function in landing pads in the user code, which in turn calls
-/// the personality function.
-_Unwind_Reason_Code _Unwind_CallPersonality(void *exception_ptr) {
-  struct _Unwind_Exception *exception_object =
-      (struct _Unwind_Exception *)exception_ptr;
-  _LIBUNWIND_TRACE_API("_Unwind_CallPersonality(exception_object=%p)",
-                       (void *)exception_object);
-
-  // Reset the selector.
-  __wasm_lpad_context.selector = 0;
-
-  // Call personality function. Wasm does not have two-phase unwinding, so we
-  // only do the cleanup phase.
-  return __gxx_personality_wasm0(
-      1, _UA_SEARCH_PHASE, exception_object->exception_class, exception_object,
-      (struct _Unwind_Context *)&__wasm_lpad_context);
-}
+_LIBUNWIND_EXPORT thread_local struct _Unwind_LandingPadContext
+    __wasm_lpad_context;
 
 /// Called by __cxa_throw.
 _LIBUNWIND_EXPORT _Unwind_Reason_Code

test/decorators.py

@@ -579,6 +579,9 @@ def metafunc(self, mode, *args, **kwargs):
     if DEBUG:
       print('parameterize:eh_mode=%s' % mode)
     if mode in {'wasm', 'wasm_legacy'}:
+      # FIXME Remove this after
+      # https://github.com/emscripten-core/emscripten/issues/27442 is fixed
+      self.skipTest('https://github.com/emscripten-core/emscripten/issues/27442')
       # Wasm EH is currently supported only in wasm backend and V8
       if self.is_wasm2js():
         self.skipTest('wasm2js does not support wasm EH/SjLj')

tools/system_libs.py

@@ -1644,7 +1644,7 @@ class libcxxabi(ExceptionLibrary, MTLibrary, DebugLibrary):
       '-std=c++23',
       '-Wno-unused-but-set-variable',
     ]
-  includes = ['system/lib/libcxx/src']
+  includes = ['system/lib/libcxx/src', 'system/lib/libunwind/include']
 
   def __init__(self, **kwargs):
     super().__init__(**kwargs)