Re: AC_CHECK_FUNCS and gcc with -Werror

[Steffen Dettmer]

On Wed, Mar 3, 2010 at 1:47 PM, Eric Blake <address@hidden> wrote:
> According to Ralf Corsepius on 3/3/2010 4:04 AM:
>> On 03/03/2010 11:52 AM, Steffen Dettmer wrote:
>>> Hi,
>>>
>>> in configure.in I have:
>>>
>>> AC_CHECK_FUNCS(printf)
>
> C89 guarantees the existence of printf - this particular use of
> AC_CHECK_FUNCS is most likely unnecessary for any modern
> machine, unless your goal is to port to an embedded system that
> doesn't provide all of C89.

Unfortunately we cannot rely on C89.
(a platform without a function actually is the easy case; the
difficult case is when a platform is able to link a function
which must not be called because it just crashes because of bad
library retargeting)

> > > cc1: warnings being treated as errors conftest.c:67:
> > > warning: conflicting types for built-in function 'printf'
> > >
> > > what to do best here?
> > Not using -Werror
>
> That's been the standard advice for years now.

Do I understand correctly that it is generally adviced to not use
the option -Werror?

Do you have some link?

In my case, most Development Rules require that sources compile
without warnings. It seems that across the team less warnings get
accidently checked in when using -Werror/-WX (our other compilers
have no such option) or what the compilers support to abort on
warnings, so it was decided to build some software with that
option.

> Don't do something if it hurts.

mmm... (I think the idea is to make a warning hurting to ensure
that it is fixed instantly and cannot be overseen / forgotten).

> -Werror is a can of worms - there is NO way to silence all
> possible warnings for all possible compilers.  It's great on a
> per-compiler build (for example, coreutils provides
> --enable-gcc-warnings, which conditionally adds -Werror to
> CFLAGS if the compiler spuports it), but only for the program
> itself, and not for the duration of the configure run.

Yes, inside configure -Werror isn't needed but for compiling
all the programs source files. How to add it for the program but
not for the configure run? Via libxyz_a_CFLAGS of all libs?

> Meanwhile, there is a patch on the table to teach autoconf 2.66 how to
> recognize and work around -Werror coupled with gcc; I hope to finish
> reviewing and apply it soon.
> http://lists.gnu.org/archive/html/bug-autoconf/2010-02/msg00040.html

ohh sounds promising :)

oki,

Steffen