No abi::__forced_unwind in libc++abi

[coffee-lord]

Commit 039b34e added a hard dependency on abi::__forced_unwind in common.h on __linux__ platform. This causes a compilation error when compiled with libc++abi:

.../spdlog/details/logger_impl.h:80:5: error: no type named '__forced_unwind' in namespace '__cxxabiv1'
    SPDLOG_CATCH_ALL
    ^~~~~~~~~~~~~~~~
.../spdlog/common.h:47:38: note: expanded from macro 'SPDLOG_CATCH_ALL'
#define SPDLOG_CATCH_ALL catch (abi::__forced_unwind&) { _err_handler("Unknown exception"); throw; } catch (...)

Relevant: cxxabi.h from libc++abi

Tested OSs: Archlinux, Gentoo (~amd64), Debian (sid)
Compiler: LLVM (trunk 317567)

• libc++
• libc++abi
• Clang 6.0.0

[gabime]

Please provide the exact linux and gcc versions.

[coffee-lord]

GCC's cxxabi.h includes cxxabi_forced.h which defines _CXXABI_FORCED_H. A weak but valid workaround to make it compile with LLVM's libc++abi would be to check for it.

#if defined(__linux__) && !defined(__ANDROID__)
#include <cxxabi.h>
#ifdef _CXXABI_FORCED_H
#define SPDLOG_CATCH_ALL catch (abi::__forced_unwind&) { _err_handler("Unknown exception"); throw; } catch (...)
#else // _CXXABI_FORCED_H
#define SPDLOG_CATCH_ALL catch (...)
#endif // _CXXABI_FORCED_H
#else // __linux__
#define SPDLOG_CATCH_ALL catch (...)
#endif // __linux__

Is abi::__forced_unwind a portable API or is it a GCC extension? LLVM might have something similar.

@manuel-schiller

[gabime]

The more I think about it the more I believe this catch(..) is bad idea. If an exception other than ‘std::exception’ happened, than it is really an unexpected one that cannot be treated correctly by spdlog. anyway, and certainly should not be masked.
So I think that catching std::exception is enough.

[coffee-lord]

It seems that abi::__forced_unwind is GCC-specific. Commit author, @manuel-schiller wanted to handle pthread_cancel() and AFAIK this kind of thread cancellation is not portable. GCC throws this exception when a thread is being cancelled but I couldn't find anything similar in LLVM. This article explains the problem.

I agree that this is probably out of scope of a logging library. Just catching std::exception should be enough unless we're missing something.

[gabime]

Fixed (kind of) in 8ca1d84

Now spdlog won't try to catch(...) - only catch(std::exception&)