compiler standards (and/or min gcc version) supported with installed headers ?

[Andreas Jaeger]

On 12/29/2012 05:57 AM, Mike Frysinger wrote:
> seems like something we should have spelled out in the manual and/or faq.
> what standards do we want to support with installed headers ?  and similarly,
> what min gcc version ?
>
> going by features.h, it seems like we support very old standards, which means
> it should be easy to support old gcc versions too.  a quick grep on my system
> shows we have __GNUC_PREREQ(2,0).

based on the comments in this thread, I wrote the following proposal. 
I've tried to separate the proposal into two discussion points: First, 
what are the requirements. Second which compiler versions to use.


* glibc needs a recent GCC compiler version to build itself (right now
   at least 4.3 required, 4.6 or newer recommended)

* Userland applications and libraries that use glibc's headers and
   libraries can be build by a variety of compilers with the following
   notes:

   - The compiler needs to support at least ISO C 90 (or C++98)
   - The compiler needs to support the type "long long"
   - GCC version X [1] is the oldest compiler supported in general (for some
     more recent hardware architectures a more recent compiler will be
     needed)
   - The glibc header files might include special optimizations for
     newer compiler versions which might not be available for older
     compilers
   - The header files for glibc use GCC Y [2] as baseline for such
     optimizations
   - Support for other compilers besides GCC might need extra patches
     which are welcome to be submitted for inclusion glibc

   - For headers shared with gnulib, other conditions do apply (the
     requirements from gnulib to support even older compilers)

To support different compilers, we would ideally not test - as today -
for a specific GCC version but for a specific feature.

So, instead of __GNUC_PREREQ(x,y) to check for a specific version in
some header file, the advise is to add a macro to features.h, like
__GLIBC_HAVE_BUILTIN_COMPLEX and use that - and that macro definition
is dependend on compiler versions.

[1], [2]:
I propose to use GCC 2.95.3 as baseline and GCC 4.3 - the same one we
use for building of glibc - for the optimization part.

Would this work?
Andreas
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