Re: [PATCH 11/12] configure: bump min required GCC to 6.3.0

[Daniel P . Berrangé]

On Tue, May 11, 2021 at 04:15:57PM +0200, Thomas Huth wrote:
> On 11/05/2021 15.26, Daniel P. Berrangé wrote:
> > Several distros have been dropped since the last time we bumped the
> > minimum required GCC version.
> > 
> > Per repology, currently shipping versions are:
> > 
> >               RHEL-8: 8.3.1
> >       Debian Stretch: 6.3.0
> >        Debian Buster: 8.3.0
> >   openSUSE Leap 15.2: 7.5.0
> >     Ubuntu LTS 18.04: 7.5.0
> >     Ubuntu LTS 20.04: 9.3.0
> >              FreeBSD: 10.3.0
> >            Fedora 33: 9.2.0
> >            Fedora 34: 11.0.1
> >              OpenBSD: 8.4.0
> >       macOS HomeBrew: 11.1.0
> > 
> > With this list Debian Stretch is the constraint at 6.3.0
> > 
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >   configure | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/configure b/configure
> > index a1a40577c9..43d2470bb6 100755
> > --- a/configure
> > +++ b/configure
> > @@ -2059,8 +2059,8 @@ cat > $TMPC << EOF
> >   #  endif
> >   # endif
> >   #elif defined(__GNUC__) && defined(__GNUC_MINOR__)
> > -# if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 8)
> > -#  error You need at least GCC v4.8 to compile QEMU
> > +# if __GNUC__ < 6 || (__GNUC__ == 6 && __GNUC_MINOR__ < 3)
> > +#  error You need at least GCC v6.3.0 to compile QEMU
> >   # endif
> >   #else
> >   # error You either need GCC or Clang to compiler QEMU
> > @@ -2068,7 +2068,7 @@ cat > $TMPC << EOF
> >   int main (void) { return 0; }
> >   EOF
> >   if ! compile_prog "" "" ; then
> > -    error_exit "You need at least GCC v4.8 or Clang v3.4 (or XCode Clang 
> > v5.1)"
> > +    error_exit "You need at least GCC v6.3 or Clang v3.4 (or XCode Clang 
> > v5.1)"
> >   fi
> >   # Accumulate -Wfoo and -Wno-bar separately.
> 
> I'm surprised that we could not remove some spots related to GCC 4.8
> compatibility here, but if I grep'ed it right, there are indeed none ...

Yeah I was surprised too. I think what's happened is that we've ended
up changing the code to avoid hitting problems from older GCC, rather
than conditionally using them. If you read git history you can find
examples of changes talking about old GCC problems being avoided.

The same for Clang.

So these change mostly free us from having to make sub-optimal in the
future.

The most immediate change we could potentially do is s/gnu99/gnu11/
for the C standard.

> thus:
> 
> Reviewed-by: Thomas Huth <thuth@redhat.com>
> 

Regards,
Daniel
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