Re: [RFC PATCH 0/1] Specify C-standard requirement for DPDK builds

[Tyler Retzlaff <roretzla@linux.microsoft.com>]

On Fri, Feb 10, 2023 at 09:52:06AM -0500, Ben Magistro wrote:
> Adding Tyler
> 
> Sort of following along on the RFC: introduce atomics [1] it seems like the
> decision to use 99 vs 11 here could make an impact on the approach taken in
> that thread.

hey Ben thanks for keeping an eye across threads on the topic. the
atomics thread is fairly long but somewhere in it i did provide a
rationale for why we can't just go straight to using C11 even if we
declared that dpdk on supports compilers >= C11.

i wish we could it would certainly make my life way easier if i could
just -std=c11 and cut & paste my way to completion. the reason why we
can't (aside from not requiring C11 compiler as a minimum) is that there
is potential issue with abi compatibility for existing applications
using non-atomic types currently passed to ABI suddenly requiring
standard atomic types. this is because _Atomic type and type are not
guaranteed to have the same size, alignment, representation etc..

anyway, i welcome us establishing c99 as a minimum for all
toolchain/platform combinations.

> 
> 1) http://mails.dpdk.org/archives/dev/2023-February/262042.html
> 
> On Fri, Feb 3, 2023 at 1:00 PM Bruce Richardson <bruce.richardson@intel.com>
> wrote:
> 
> > On Fri, Feb 03, 2023 at 11:45:04AM -0500, Ben Magistro wrote:
> > >    In our case we have other libraries that we are using that have
> > >    required us to specify a minimum c++ version (14/17 most recently for
> > >    one) so it doesn't feel like a big ask/issue to us (provided things
> > >    don't start conflicting...hah; not anticipating any issue).  Our
> > >    software is also used internally so we have a fair bit of control over
> > >    how fast we can adopt changes.
> > >    This got me wondering what some other projects in the DPDK ecosystem
> > >    are saying/doing around language standards/gcc versions.  So some
> > quick
> > >    checking of the projects I am aware of/looked at/using...
> > >    * trex: cannot find an obvious minimum gcc requirement
> > >    * tldk: we are running our own public folk with several fixes, need to
> > >    find time to solve the build sys change aspect to continue providing
> > >    patches upstream; I know I have hit some places where it was easier to
> > >    say the new minimum DPDK version is x at which point you just adopt
> > the
> > >    minimum requirements of DPDK
> > >    * ovs: looks to be comfortable with an older gcc still
> > >    * seastar: seems to be the most aggressive with adopting language
> > >    standards/compilers I've seen [1] and are asking for gcc 9+ and cpp17+
> > >    * ans: based on release 19.02 (2019), they are on gcc >= 5.4 [2] and
> > is
> > >    the same on the main README file
> > >    I do understand the concern, but if no one is voicing an
> > >    opinion/objection does that mean they agree with/will not be affected
> > >    by the change....
> > >    1) [1]https://docs.seastar.io/master/md_compatibility.html
> > >    2) [2]https://github.com/ansyun/dpdk-ans/releases
> > >    Cheers
> > >
> > Thanks for the info.
> > I also notice that since gcc 5, the default language version used - if none
> > is explicitly specified - is gnu11 (or higher for later versions). Clang
> > seems to do something similar, but not sure at what point it started
> > defaulting to a standard >=c11.
> >
> > /Bruce
> >