Source code
Revision control
Copy as Markdown
Other Tools
From 0991d7b8fd01546aaf537a6238227100570f8236 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
Date: Thu, 12 Feb 2026 00:31:09 +0200
Subject: [PATCH] [libunwind] Fix building with EXCEPTION_DISPOSITION as enum
(#180513)
On Windows, libunwind is normally only built in mingw mode; it's not
relevant for MSVC targets. (Attempting to build it is entirely blocked
in CMake, see [1]).
In mingw headers, the type EXCEPTION_DISPOSITION is defined as an int
while it is an enum in the MSVC vcruntime headers.
However, in addition to the canonical enum members, we also use a value
which has no assigned enum member. In older mingw-w64 headers, there was
a define for this value, 4, with the name ExceptionExecuteHandler, but
that was removed in [2]. The libunwind code reference this value just by
the literal value 4, with a comment referencing it as
ExceptionExecuteHandler.
This extra enum value isn't passed to the outside Microsoft runtime, but
is only used to pass values from one part of libunwind to another; this
handling is necessary for the forced_unwind{1-3}.pass.cpp tests to
succeed.
If the mingw-w64 headers would define EXCEPTION_DISPOSITION as an enum,
just like the MSVC vcruntime headers, then we'd run into build errors
and warnings like this:
llvm-project/libunwind/src/Unwind-seh.cpp:166:14: error: cannot initialize return object of type 'EXCEPTION_DISPOSITION' (aka 'enum _EXCEPTION_DISPOSITION') with an rvalue of type 'int'
166 | return 4 /* ExceptionExecuteHandler in mingw */;
| ^
llvm-project/libunwind/src/Unwind-seh.cpp:185:14: error: cannot initialize return object of type 'EXCEPTION_DISPOSITION' (aka 'enum _EXCEPTION_DISPOSITION') with an rvalue of type 'int'
185 | return 4 /* ExceptionExecuteHandler in mingw */;
| ^
llvm-project/libunwind/src/Unwind-seh.cpp:272:8: warning: case value not in enumerated type 'EXCEPTION_DISPOSITION' (aka 'enum _EXCEPTION_DISPOSITION') [-Wswitch]
272 | case 4 /*ExceptionExecuteHandler*/:
| ^
Fix these cases by adding explicit casts between EXCEPTION_DISPOSITION
and int.
A (partial) similar change was proposed in [3], but the author never
followed up on the discussion, and the PR was later closed.
[1] b0b546d44777eb1fa25995384876bd14a006a929
---
libunwind/src/Unwind-seh.cpp | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)
diff --git a/libunwind/src/Unwind-seh.cpp b/libunwind/src/Unwind-seh.cpp
index 110c5987c3f1..0b1930b44d1c 100644
--- a/libunwind/src/Unwind-seh.cpp
+++ b/libunwind/src/Unwind-seh.cpp
@@ -163,7 +163,7 @@ _GCC_specific_handler(PEXCEPTION_RECORD ms_exc, PVOID frame, PCONTEXT ms_ctx,
// If we were called by __libunwind_seh_personality(), indicate that
// a handler was found; otherwise, initiate phase 2 by unwinding.
if (ours && ms_exc->NumberParameters > 1)
- return 4 /* ExceptionExecuteHandler in mingw */;
+ return static_cast<EXCEPTION_DISPOSITION>(4);
// This should never happen in phase 2.
if (IS_UNWINDING(ms_exc->ExceptionFlags))
_LIBUNWIND_ABORT("Personality indicated exception handler in phase 2!");
@@ -182,7 +182,7 @@ _GCC_specific_handler(PEXCEPTION_RECORD ms_exc, PVOID frame, PCONTEXT ms_ctx,
// a handler was found; otherwise, it's time to initiate a collided
// unwind to the target.
if (ours && !IS_UNWINDING(ms_exc->ExceptionFlags) && ms_exc->NumberParameters > 1)
- return 4 /* ExceptionExecuteHandler in mingw */;
+ return static_cast<EXCEPTION_DISPOSITION>(4);
// This should never happen in phase 1.
if (!IS_UNWINDING(ms_exc->ExceptionFlags))
_LIBUNWIND_ABORT("Personality installed context during phase 1!");
@@ -259,13 +259,12 @@ __libunwind_seh_personality(int version, _Unwind_Action state,
(void *)disp_ctx->LanguageHandler, (void *)&ms_exc,
(void *)disp_ctx->EstablisherFrame,
(void *)disp_ctx->ContextRecord, (void *)disp_ctx);
- EXCEPTION_DISPOSITION ms_act = disp_ctx->LanguageHandler(&ms_exc,
- (PVOID)disp_ctx->EstablisherFrame,
- disp_ctx->ContextRecord,
- disp_ctx);
+ int ms_act = static_cast<int>(
+ disp_ctx->LanguageHandler(&ms_exc, (PVOID)disp_ctx->EstablisherFrame,
+ disp_ctx->ContextRecord, disp_ctx));
_LIBUNWIND_TRACE_UNWINDING("__libunwind_seh_personality() LanguageHandler "
"returned %d",
- (int)ms_act);
+ ms_act);
switch (ms_act) {
case ExceptionContinueExecution: return _URC_END_OF_STACK;
case ExceptionContinueSearch: return _URC_CONTINUE_UNWIND;
--
2.53.0