https://github.com/mstorsjo created
https://github.com/llvm/llvm-project/pull/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
[2]
https://github.com/mingw-w64/mingw-w64/commit/2de6703961c0d519046b841f7b392a040e1e5b55
[3] https://github.com/llvm/llvm-project/pull/159293
From 6cbc7b387127e9aea3024ca23caa7b64672e32b3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <[email protected]>
Date: Mon, 9 Feb 2026 14:13:58 +0200
Subject: [PATCH] [libunwind] Fix building with EXCEPTION_DISPOSITION as enum
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
[2]
https://github.com/mingw-w64/mingw-w64/commit/2de6703961c0d519046b841f7b392a040e1e5b55
[3] https://github.com/llvm/llvm-project/pull/159293
---
libunwind/src/Unwind-seh.cpp | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/libunwind/src/Unwind-seh.cpp b/libunwind/src/Unwind-seh.cpp
index 110c5987c3f1a..fe905f8765e17 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!");
@@ -266,7 +266,7 @@ __libunwind_seh_personality(int version, _Unwind_Action
state,
_LIBUNWIND_TRACE_UNWINDING("__libunwind_seh_personality() LanguageHandler "
"returned %d",
(int)ms_act);
- switch (ms_act) {
+ switch (static_cast<int>(ms_act)) {
case ExceptionContinueExecution: return _URC_END_OF_STACK;
case ExceptionContinueSearch: return _URC_CONTINUE_UNWIND;
case 4 /*ExceptionExecuteHandler*/:
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