Re: [PATCH] PowerPC: Define __PTHREAD_MUTEX_HAVE_ELISION to 0

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Tue, 25 Mar 2014, Adhemerval Zanella wrote:

> I agree with you, but the patch to check if it is defined in 
> nptl/sysdeps/pthread/pthread.h was rejected: 
> https://sourceware.org/ml/libc-alpha/2014-03/msg00494.html. So I just 
> folowed the way x86_64 and s390 does. If this was just an warning I'd 
> rework it to make it more general, as Roland as suggested in 
> https://sourceware.org/ml/libc-alpha/2014-03/msg00501.html; but it is 
> breaking 'make check' build. So my preference now is let it as and focus 
> on a proper fix, if any, after.

I suggest an installed header bits/pthread-elision.h that defines 
__PTHREAD_MUTEX_HAVE_ELISION to an appropriate value.  That avoids every 
architecture without elision needing to define this value in separate 
bits/pthreadtypes.h files.

I also strongly advise *not* applying any architecture-specific fixes for 
-Wundef warnings that appear not to be architecture-specific without:

(a) working out the correct general solution;

(b) if not fixing all architectures, listing the issue and unfixed 
architectures on <https://sourceware.org/glibc/wiki/PortStatus>.

We've made a lot of progress on avoiding architectures diverging from each 
other.  Instead of ad hoc fixes for particular architectures, follow 
Siddhesh's example for fixing bits/mathdef.h (where he fixed all affected 
versions of the header).

By all means just fix issues where the issue and fix appear genuinely 
architecture-specific, rather than relating to a header for which many 
architectures have their own versions all of which would need fixing 
similarly.  But for architecture-independent issues like this, it's 
necessary to take the extra steps to avoid divergence and ensure agreement 
over the right fix for all architectures.

-- 
Joseph S. Myers
joseph@codesourcery.com