[PATCH v16 00/60] remove use of VLAs for Windows

[Bruce Richardson]

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 at 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