From: Brandon Casey <casey@nrlssc.navy.mil>
Date: Tue, 21 Jul 2009 15:34:30 GMT
Subject: Re: [PATCH] configure: use AC_SEARCH_LIBS instead of AC_CHECK_LIB
Message-ID: <qSl_KXgcJD_1H47Nrg3FwRdtL-WxwLP1_aueDE8gN-By3M0uJOpw1w@cipher.nrlssc.navy.mil>
In-Reply-To: <4A65DCB9.3030207@gnu.org>

Paolo Bonzini wrote:
> 
>> With AC_SEARCH_LIBS, which of [action-if-found] or [action-if-not-found]
>> is executed if the function is found in the standard c library i.e.
>> "calling
>> `AC_LINK_IFELSE([AC_LANG_CALL([], [function])])' first with no
>> libraries"?
>> Is the answer neither?  If the answer is [action-if-found], won't the
>> NEEDS_LIBGEN=YesPlease be set when the function is found in the c
>> library?
> 
> It evaluates the action-if-found and adds nothing to LIBS.  Instead, if
> it is found in a library, it evaluates the action-if-found after adding
> (actually prepending) -lBLAH to LIBS.

That's what I suspected.  It means we can't have NEEDS_SOMETHING=true in
the action-if-found parameter when using AC_SEARCH_LIBS since that may cause
the Makefile to append a library requirement when none is necessary.

-brandon