Minimum GCC version for building glibc

[Joseph Myers]

On Wed, 5 Nov 2014, Mike Frysinger wrote:

> any time you use a gcc feature you must review to see if it's supported by the 
> versions we support.  bumping the min gcc version doesn't preclude that.  if 

No (even if autoconf kept testing for ISO C90 features long after doing so 
was unnecessary).  You just need to be aware of what's recent and not care 
about the versions in which longstanding features were introduced - and 
expanding the set of features that count as longstanding reduces the load 
of keeping track of what's recent (you only need to review if using a 
feature that might be on the borderline, and otherwise can either use 
features without thinking about compiler versions, or know that a feature 
is only usable conditionally, either of which is much more efficient than 
needing to check).

> > I think -Werror makes it more likely building with old versions will break 
> > when they aren't actively tested.  We also now have a clear use for 
> > diagnostic pragmas, new in 4.6, to allow more selective disabling of 
> > particular warnings together with -Werror.
> 
> -Werror makes sense when building from git / maintainer mode, but not in any 
> other scenario (such as unpacking release tarballs and running plain configure).

Defaulting to disabling -Werror for releases (or based on compiler 
version) was previously objected to in 
<https://sourceware.org/ml/libc-alpha/2012-08/msg00404.html>.

> so your argument hinges on whether the new atomic logic should require gcc 4.7.  
> that should probably shake out in the relevant threads and once it has, you've 
> got a compelling reason for dropping <4.7.  but i still don't see any 
> justification for, if we are retaining 4.6, why we should drop 4.4 & 4.5.

It's already been stated - using #pragma GCC diagnostic push/pop to help 
with -Werror usage.

-- 
Joseph S. Myers
joseph@codesourcery.com