Re: [Patch, libiberty] Fix build regression

[Ralf Wildenhues <Ralf dot Wildenhues at gmx dot de>]

* Anthony Green wrote on Fri, Nov 19, 2010 at 11:09:36PM CET:
> This patch fixes a recent libiberty build regression discussed in this
> thread:
>   http://gcc.gnu.org/ml/gcc-patches/2010-11/msg01998.html
> 
> If we know we aren't going to be able to build executables, simply emit
> a warning saying that we can't link (instead of exiting with an error),
> and mention that we're assuming prctl does not exist for this target.
> 
> Ok to commit?

A better fix is to actually allow the answer to the test to be correct
even in the no-link case.  For that, cache the test result.  It may then
be useful to move the test to a more appropriate place, such as after
the code that sets all the cache variables based on $host in the no-link
case.  That way port maintainers can enter the right answers for this
test there, and if not given users can still configure toplevel with
  .../configure target_configargs=libiberty_cv_prctl_PR_SET_NAME=yes

or so.

Here's how a cached version of the test would look like (untested!),
including a couple more fixlets:

AC_CACHE_CHECK([for prctl PR_SET_NAME],
  [libiberty_cv_prctl_PR_SET_NAME],
  [AC_LINK_IFELSE(
     [AC_LANG_PROGRAM([[#include <sys/prctl.h>]],
        [[return (prctl(PR_SET_NAME, "foo") == 0) ? 0 : 1;]])],
     [libiberty_cv_prctl_PR_SET_NAME=yes],
     [libiberty_cv_prctl_PR_SET_NAME=no])])

if test "$libiberty_cv_prctl_PR_SET_NAME" = yes; then
  AC_DEFINE(HAVE_PRCTL_SET_NAME, 1,
            [Define if you have prctl PR_SET_NAME]))
fi

Thanks,
Ralf

> 2010-11-19  Anthony Green  <green@moxielogic.com>
> 
> 	* configure.ac: Don't run link tests if we can't build
> 	executables.
> 	* configure: Rebuilt.

> --- libiberty/configure.ac	(revision 166958)
> +++ libiberty/configure.ac	(working copy)
> @@ -538,15 +538,20 @@
>  AC_SUBST(CHECK)
>  AC_SUBST(target_header_dir)
>  
> -# check for prctl PR_SET_NAME
> -AC_LINK_IFELSE([AC_LANG_SOURCE([[
> -#include <sys/prctl.h>
> -int main()
> -{
> -  return (prctl(PR_SET_NAME, "foo") == 0) ? 0 : 1;
> -}
> -]])], AC_DEFINE(HAVE_PRCTL_SET_NAME, 1,
> -	[Define if you have prctl PR_SET_NAME]))
> +if test x$gcc_no_link = xyes; then
> +  AC_MSG_WARN([
> +*** Cannot link executables.  Assuming target does not have prctl function.])
> +else
> +  # check for prctl PR_SET_NAME
> +  AC_LINK_IFELSE([AC_LANG_SOURCE([[
> +  #include <sys/prctl.h>
> +  int main()
> +  {
> +    return (prctl(PR_SET_NAME, "foo") == 0) ? 0 : 1;
> +  }
> +  ]])], AC_DEFINE(HAVE_PRCTL_SET_NAME, 1,
> +  	[Define if you have prctl PR_SET_NAME]))
> +fi
>  
>  case "${host}" in
>    *-*-cygwin* | *-*-mingw*)