[cfe-dev] [libcxxabi]: why does not the default unexpected handler call terminate() in libcxxabi?

Howard Hinnant hhinnant at apple.com
Tue Sep 18 07:49:39 PDT 2012

On Sep 18, 2012, at 6:28 AM, soaliap <soaliap at 126.com> wrote:

> When I executed testsuites in
> libcxx/test/depr/exception.unexpected/set.unexpected directory, it failed to
> verify the default unexpected handler.
> I saw the code in libcxx/src/exception.cpp:
> ----------------------------------------------------------------------
> #if __APPLE__
>  //...
> #elif defined(LIBCXXRT) || __has_include(<cxxabi.h>)
>  // ...
> #else  // __has_include(<cxxabi.h>)
>  static std::terminate_handler  __terminate_handler;
>  static std::unexpected_handler __unexpected_handler; // default value is 0
> #endif  // __has_include(<cxxabi.h>)
> ----------------------------------------------------------------------
> __unexpected_handler is a static varible, so its default value is 0, then I
> plan to use the __cxa_unexpected_handler in libc++abi instead of
> __unexpected_handler. But its default value is default_unexpected_handler,
> and it indirectly calls abort_message() rather than std::terminate().
> I saw the section "D.11.1 Type unexpected_handler" of n3242.pdf, it says:
>    "Default behavior: The implementation's default unexpected_handler calls
> terminate()."
> Now I'm confused about why the default unexpected handler does not call
> terminate() in libcxxabi.
> I think it's the reason causes the two testsuites failed:
> ----------------------------------------------------------------------
> (1)
> libcxx/test/depr/exception.unexpected/set.unexpected/get_unexpected.pass.cpp
> (2)
> libcxx/test/depr/exception.unexpected/set.unexpected/set_unexpected.pass.cpp
> ----------------------------------------------------------------------
> Is it a bug of libc++abi, or I misunderstood it? Who can give me some
> advice? Thanks very much!

I believe the bottom line is that libcxx/libcxxabi hasn't been ported to your platform.  The 3rd #else/#endif branch in libcxx/src/exception.cpp is not being used by anyone that I'm aware of.

I recommend getting into the branch __has_include(<cxxabi.h>) which will #define _LIBCPPABI_VERSION (which comes from libcxxabi.  But this is porting work you (or someone) will have to do.


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