According to Dmitry V. Levin on 1/21/2010 4:40 PM: > Hi, > > There is no news that AC_CHECK_FUNC fails to find built-in functions when > either AC_LANG_WERROR is used or -Werror is included in CFLAGS:
Yes, this is a well-known and frequently reported issue, and our usual response has been to tell people "don't do it if it hurts". > For a long time I maintain a patch that remedies this problem. While the > patch is probably not quite suitable for inclusion as is, it is known to > work. I've updated it for the HEAD and decided to give it a chance to be > discussed here. I hope the idea behind this patch could be used for a > more acceptable fix. Indeed - proposing patches is always a better approach than complaining. No promises on when I can give this a deep-down review, but at least you've got the ball rolling. > +m4_define([AC_LANG_FUNC_LINK_TRY_GCC_BUILTIN(C)], > +[AC_LANG_PROGRAM( > +[#ifndef __GNUC__ > +choke me > +#else > +#undef $1 > +/* Declare this function with same prototype as __builtin_$1. > + This removes warning about conflicting type with builtin */ > +__typeof__(__builtin_$1) $1; > + > +__typeof__(__builtin_$1) *f = $1; > +#endif > +], [return f != $1;])]) Since we are really only caring about silencing gcc -Werror, I see no reason to force a compilation for non-gcc compilers. But the idea of exploiting __GNUC__ and known gcc extensions, to avoid conflicts with __builtin_* functions, does seem appealing, especially since we now have the machinery to do it only once in a function rather than bloating every use of AC_CHECK_FUNC throughout the configure file. > [AC_LINK_IFELSE([AC_LANG_FUNC_LINK_TRY($[]2)], > [AS_VAR_SET([$[]3], [yes])], > - [AS_VAR_SET([$[]3], [no])])]) > + [AC_LINK_IFELSE([AC_LANG_FUNC_LINK_TRY_GCC_BUILTIN($[]2)], > + [AS_VAR_SET([$[]3], [yes])], > + [AS_VAR_SET([$[]3], [no])])])]) > AS_LINENO_POP > ])# _AC_CHECK_FUNC_BODY It would be even slicker to do this without having to recompile (that is, rewrite AC_LANG_FUNC_LINK_TRY to use the new logic, rather than making AC_CHECK_FUNC call AC_LINK_IFELSE twice). -- Don't work too hard, make some time for fun as well! Eric Blake e...@byu.net
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