From ab389df4e10b3aec62169bacf37f03dafb4089fd Mon Sep 17 00:00:00 2001
From: Heejin Ahn <aheejin@gmail.com>
Date: Sun, 20 Sep 2026 09:47:04 +0000
Subject: [PATCH] [EH] Apply coop threading fix from LLVM

After https://github.com/llvm/llvm-project/pull/222747, user code will
not directly access `__was_lpad_context` but instead get its address via
`_Unwind_GetWasmLPadContext` function call. This is done for WASIp3
cooperative threading + dynamic library support, but doing this
unconditionally in all cases is simple and does not have any downsides.

Because we update our LLVM libraries perodically, to make
https://github.com/llvm/llvm-project/pull/222747 pass our autorollers,
this applies its library side changes here first to match its codegen
changes.
---
 system/lib/libcxxabi/src/cxa_personality.cpp | 8 +++++---
 system/lib/libunwind/include/unwind_wasm.h   | 5 ++++-
 system/lib/libunwind/src/Unwind-wasm.c       | 7 ++++++-
 tools/system_libs.py                         | 4 ++--
 4 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/system/lib/libcxxabi/src/cxa_personality.cpp b/system/lib/libcxxabi/src/cxa_personality.cpp
index f77c5393795ca..5cc7809385d5d 100644
--- a/system/lib/libcxxabi/src/cxa_personality.cpp
+++ b/system/lib/libcxxabi/src/cxa_personality.cpp
@@ -1126,13 +1126,15 @@ __gxx_personality_seh0(PEXCEPTION_RECORD ms_exc, void *this_frame,
 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;
 
+  struct _Unwind_LandingPadContext* context = _Unwind_GetWasmLPadContext();
+
   // Reset the selector.
-  __wasm_lpad_context.selector = 0;
+  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);
+  return __gxx_personality_imp(
+      1, _UA_SEARCH_PHASE, exception_object->exception_class, exception_object, (struct _Unwind_Context*)context);
 }
 #endif
 
diff --git a/system/lib/libunwind/include/unwind_wasm.h b/system/lib/libunwind/include/unwind_wasm.h
index 7bf3f30562bd8..f06e646b296ac 100644
--- a/system/lib/libunwind/include/unwind_wasm.h
+++ b/system/lib/libunwind/include/unwind_wasm.h
@@ -22,6 +22,9 @@ struct _Unwind_LandingPadContext {
 
 // Communication channel between compiler-generated user code and personality
 // function
-extern thread_local struct _Unwind_LandingPadContext __wasm_lpad_context;
+#ifdef __cplusplus
+extern "C"
+#endif
+    struct _Unwind_LandingPadContext *_Unwind_GetWasmLPadContext(void);
 
 #endif // __WASM_UNWIND_H__
diff --git a/system/lib/libunwind/src/Unwind-wasm.c b/system/lib/libunwind/src/Unwind-wasm.c
index 6ee4b1fd36ee4..f85985e2db1d7 100644
--- a/system/lib/libunwind/src/Unwind-wasm.c
+++ b/system/lib/libunwind/src/Unwind-wasm.c
@@ -19,9 +19,14 @@
 #include "unwind.h"
 #include <threads.h>
 
-_LIBUNWIND_EXPORT thread_local struct _Unwind_LandingPadContext
+thread_local struct _Unwind_LandingPadContext
     __wasm_lpad_context;
 
+_LIBUNWIND_EXPORT struct _Unwind_LandingPadContext *
+_Unwind_GetWasmLPadContext(void) {
+  return &__wasm_lpad_context;
+}
+
 /// Called by __cxa_throw.
 _LIBUNWIND_EXPORT _Unwind_Reason_Code
 _Unwind_RaiseException(_Unwind_Exception *exception_object) {
diff --git a/tools/system_libs.py b/tools/system_libs.py
index f73efe18d6eaf..0c4b682414008 100644
--- a/tools/system_libs.py
+++ b/tools/system_libs.py
@@ -1732,8 +1732,8 @@ class libcxx(ExceptionLibrary, MTLibrary, DebugLibrary):
 
 class libunwind(ExceptionLibrary, MTLibrary):
   name = 'libunwind'
-  # Because calls to _Unwind_CallPersonality are generated during LTO, libunwind
-  # can't currently be part of LTO.
+  # Because calls to _Unwind_GetWasmLPadContext are generated during LTO,
+  # libunwind can't currently be part of LTO.
   # See https://bugs.llvm.org/show_bug.cgi?id=44353
   force_object_files = True