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[EH] Apply coop threading fix from LLVM #27753

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Merged
aheejin merged 1 commit into from
Sep 21, 2026
+17 −7
Merged

[EH] Apply coop threading fix from LLVM #27753

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8 changes: 5 additions & 3 deletions system/lib/libcxxabi/src/cxa_personality.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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

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5 changes: 4 additions & 1 deletion system/lib/libunwind/include/unwind_wasm.h
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Expand Up @@ -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__
7 changes: 6 additions & 1 deletion system/lib/libunwind/src/Unwind-wasm.c
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Expand Up @@ -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) {
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4 changes: 2 additions & 2 deletions tools/system_libs.py
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Expand Up @@ -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,

@aheejin aheejin Sep 20, 2026

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Drive-by fix: _Unwind_CallPersonality was deleted from the library in #27445 but I forgot to remove this, but now we have a new function

# libunwind can't currently be part of LTO.
# See https://bugs.llvm.org/show_bug.cgi?id=44353
force_object_files = True

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