Fix compilation errors

[silver-popov]

Implicit conversion of int to enum causes an error in CLang 21.

[llvmbot]

@llvm/pr-subscribers-libunwind

Author: Igor Popov (silver-popov)

Changes

Implicit conversion of int to enum causes an error in CLang 21.

---

Full diff: https://github.com/llvm/llvm-project/pull/159293.diff

1 Files Affected:

• (modified) libunwind/src/Unwind-seh.cpp (+2-2)

diff --git a/libunwind/src/Unwind-seh.cpp b/libunwind/src/Unwind-seh.cpp
index 8b83f10615f22..60571b3079887 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 (EXCEPTION_DISPOSITION)4 /* ExceptionExecuteHandler in mingw */;
     // This should never happen in phase 2.
     if (IS_UNWINDING(ms_exc->ExceptionFlags))
       _LIBUNWIND_ABORT("Personality indicated exception handler in phase 2!");
@@ -181,7 +181,7 @@ _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 (EXCEPTION_DISPOSITION)4 /* ExceptionExecuteHandler in mingw */;
     // This should never happen in phase 1.
     if (!IS_UNWINDING(ms_exc->ExceptionFlags))
       _LIBUNWIND_ABORT("Personality installed context during phase 1!");

[mstorsjo]

This had me a bit surprised, because I build the latest libunwind nightly, with the latest clang, and haven't run into this.

But the reason for that, is that mingw has got EXCEPTION_DISPOSITION defined as int, see https://github.com/mingw-w64/mingw-w64/blob/v13.0.0/mingw-w64-headers/crt/excpt.h#L19-L26 - while MSVC headers have it as an actual enum.

So this issue is observable only if building in MSVC mode. IIRC there are a few other issues if building libunwind in MSVC mode as well (and libunwind isn't really very useful for much in a MSVC mode environment anyway - but if you have a specific use case for it there I'm interested in hearing!).

Anyway, the change itself looks fine to me (although we perhaps should use static_cast<>() instead).