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Date: Thu, 23 Jan 2025 08:37:59 -0800
From: Andre Muezerie <andremue@linux.microsoft.com>
To: Bruce Richardson <bruce.richardson@intel.com>
Cc: David Marchand <david.marchand@redhat.com>, dev@dpdk.org,
 konstantin.ananyev@huawei.com, thomas@monjalon.net
Subject: Re: [PATCH v16 00/60] remove use of VLAs for Windows
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On Thu, Jan 23, 2025 at 12:43:04PM +0000, Bruce Richardson wrote:
> On Thu, Jan 23, 2025 at 12:58:49PM +0100, David Marchand wrote:
> > On Tue, Jan 14, 2025 at 3:32 AM Andre Muezerie
> > <andremue@linux.microsoft.com> wrote:
> > >
> > > As per guidance technical board meeting 2024/04/17. This series
> > > removes the use of VLAs from code built for Windows for all 3
> > > toolchains. If there are additional opportunities to convert VLAs
> > > to regular C arrays please provide the details for incorporation
> > > into the series.
> > >
> > > MSVC does not support VLAs, replace VLAs with standard C arrays
> > > or alloca(). alloca() is available for all toolchain/platform
> > > combinations officially supported by DPDK.
> > >
> > > v16:
> > >   * remove -Wvla from drivers/common/mlx5/meson.build and
> > >     drivers/common/qat/meson.build
> > >
> > > v15:
> > >   * inverted some of the logic added during v14:
> > >     add -Wvla to meson build files in app and lib directories, adding
> > >     -Wno-vla to the few subdirectories which are not yet VLA free
> > >
> > > v14:
> > >   * add -Wvla to meson build for directories that are VLA free
> > >     under app, lib, drivers. This is to ensure that new VLAs are
> > >     not added to these directories in the future.
> > 
> > Thanks for working on this topic.
> > 
> > I see there is some back and forth on the topic of passing -Wvla.
> > It would be less fragile to put a -Wla in a upper level meson.build
> > (like config/meson.build for example), then disable explicitly in the
> > parts that are not ready.
> > 
> > Something like:
> > diff --git a/config/meson.build b/config/meson.build
> > index 6aaad6d8a4..be603bd45b 100644
> > --- a/config/meson.build
> > +++ b/config/meson.build
> > @@ -348,6 +348,17 @@ foreach arg: warning_flags
> >      endif
> >  endforeach
> > 
> > +if cc.has_argument('-Wvla')
> > +    add_project_arguments('-Wvla', language: 'c')
> > +    if not is_windows
> > +        no_vla_cflag = '-Wno-vla'
> > +    else
> > +        no_vla_cflag = []
> > +    endif
> > +else
> > +    no_vla_cflag = []
> > +endif
> > +
> 
> Minor simplification suggestion, put "no_vla_cflag = []" outside the
> conditionals at the start, as the default value. Save having multiple
> copies of that assignment, and having to do "else" legs.
> 
> /Bruce

These look like great improvements. I especially like the idea of using -Wvla from the very top.