Am 05.08.2010 00:20, schrieb Arun Sharma:
>>>> AC_CHECK_LIB([unwind], [_Unwind_Backtrace], [], [ AC_MSG_ERROR([*** Could
>>>> not find libunwind ***]) ])
>>>
>>> _Unwind_Backtrace could be provided by other libraries as well. I'd
>>> test for something specific to libunwind (eg: unw_step).
>>
>> This is not a good idea. unw_step is not a symbol from the
>> library but only a define. So the check definitely fails.
>
> The problem is: if you configure libunwind with
> --enable_cxx_exceptions=no (which is the default on x86, arm,
> mips), you'll not have these symbols defined.
>
> True - unw_step gets rewritten as _UL${plat}_step (see
> tests/check-namespace.sh) - but why should it be a problem for
> writing an autoconf macro as long as you're including the right
> header file with #define unw_step ...?
That's not the way autoconf (especially configure) works. To check if a symbol
is available in a library it temporarily creates simple test source code
calling this symbol and tries to link with the library.
Steffen
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