On Wed, Jan 09, 2019 at 12:25:43PM +0100, Thomas Huth wrote: > On 2019-01-09 11:58, Daniel P. Berrangé wrote: > > On Mon, Jan 07, 2019 at 11:45:26AM +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 are > >> GCC v4.8 and Clang v3.4 now, and both basically support "gnu11" already, > >> this seems to be a good choice. > > > > In 4.x gnu11 is marked as experimental. I'm not really comfortable > > using experimental features - even if its warning free there's a risk > > it would silently mis-compile something. > > > > gnu99 is ok with 4.x - it is merely "incomplete". > > gnu11 has the big advantage that it also fixes the problem with > duplicated typedefs that are reported by older versions of Clang. > > Are you sure about the experimental character in 4.x? I just looked at > https://gcc.gnu.org/onlinedocs/gcc-4.8.5/gcc/Standards.html and it says: > > "A fourth version of the C standard, known as C11, was published in 2011 > as ISO/IEC 9899:2011. GCC has limited incomplete support for parts of > this standard, enabled with -std=c11 or -std=iso9899:2011." > > It does not say anything about "experimental" there. The word > "experimental" is only used for the C++ support, but we hardly have C++ > code in QEMU -- if you worry about that, I could simply drop the > "-std=gnu++11" part from my patch?
I was looking at the "info gcc" docs on RHEL7, gcc-4.8.5-16.el7_4.1.x86_64: "3.4 Options Controlling C Dialect ....snip... 'c11' 'c1x' 'iso9899:2011' ISO C11, the 2011 revision of the ISO C standard. Support is incomplete and experimental. The name 'c1x' is deprecated. ....snip... 'gnu11' 'gnu1x' GNU dialect of ISO C11. Support is incomplete and experimental. The name 'gnu1x' is deprecated." Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|