Re: [Qemu-devel] [PATCH v2] configure: Force the C standard to gnu99

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jan 09, 2019 at 03:51:33PM +0100, Thomas Huth wrote:
> On 2019-01-09 15:31, Daniel P. Berrangé wrote:
> > On Wed, Jan 09, 2019 at 03:24:29PM +0100, Thomas Huth wrote:
> >> Different versions of GCC and Clang use different versions of the C standard.
> >> This repeatedly caused problems already, e.g. with duplicated typedefs:
> >>
> >>  https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg05829.html
> >>
> >> or with for-loop variable initializers:
> >>
> >>  https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg00237.html
> >>
> >> To avoid these problems, we should enforce the C language version to the
> >> same level for all compilers. Since our minimum compiler versions is
> >> GCC v4.8, our best option is "gnu99" right now ("gnu17" is not available
> >> there yet, and "gnu11" is marked as "experimental").
> >>
> >> Signed-off-by: Thomas Huth <thuth@redhat.com>
> >> ---
> >>  v2: Use gnu99 instead of gnu11
> >>
> >>  configure | 5 +++--
> >>  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> > 
> >> diff --git a/configure b/configure
> >> index b9f34af..721ade7 100755
> >> --- a/configure
> >> +++ b/configure
> >> @@ -105,7 +105,8 @@ update_cxxflags() {
> >>      for arg in $QEMU_CFLAGS; do
> >>          case $arg in
> >>              -Wstrict-prototypes|-Wmissing-prototypes|-Wnested-externs|\
> >> -            -Wold-style-declaration|-Wold-style-definition|-Wredundant-decls)
> >> +            -Wold-style-declaration|-Wold-style-definition|-Wredundant-decls|\
> >> +            -std=gnu99)
> > 
> > IIUC this is to  drop  -std=gnu99 from CXXFLAGS, so C++ code (only the
> > guest-agent on Win32 IIUC) will use the compiler default still.
> 
> We also use it for the capstone disassembler and disas/libvixl.
> 
> > We could consider also setting a suitable -std for CXXFLAGS too in future
> > though...
> 
> Shall I send a v3 with "-std=gnu++98" (which seems to be the only usable
> option right now), or shall we wait until we really hit a problem with
> the C++ code?

I'd have a slight preference for adding a C++ suitable -std now
just to give us a more predictable build setup. I don't consider
it a blocker though, hence my R-b on this v2 patch as it is now.

Regards,
Daniel
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