Re: [PATCH 1/2] meson/mlx5: Suppress -Wunused-value diagnostic

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 12 Apr 2024 13:13:16 +0200
Sebastian Brzezinka <sebastian.brzezinka@intel.com> wrote:

> From: Alexey Marchuk <alexeymar@mellanox.com>
> 
> mlx5 common library checks if several symbols/definitions
> are presented in system header files. If some are not
> presented, they will be enabled by mlx5_glue library.
> The problem appears with clang and '-Werror' - code
> generated by meson is not compiled due to unused variable:
> 
> Code:
> 
>         #include <infiniband/mlx5dv.h>
>         int main(void) {
>             /* If it's not defined as a macro, try to use as a symbol */
>             #ifndef mlx5dv_create_flow_action_packet_reformat
>                 mlx5dv_create_flow_action_packet_reformat;
>             #endif
>             return 0;
>         }
> Compiler stdout:
> 
> Compiler stderr:
>  /hpc/local/work/alexeymar/repo/spdk/dpdk/build-tmp/meson-private/tmp5obnak86/testfile.c:6:17: error: expression result unused [-Werror,-Wunused-value]
>                 mlx5dv_create_flow_action_packet_reformat;
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> As result, almost all symbols are enabled in mlx5_glue while
> they exist is system headers. As result, we get multiple
> symbols redefenitions when we compile mlx5_common.
> As a solution for this problem we can suppress
> -Wunused-vaurable using pragma
> 
> DPDK 23.11 note:
> Starting with commit below, all cflags are passed to the has_header_symbol().
> (33d6694) build: use C11 standard
> To make sure that the symbol is properly detected, the pedantic flags needs to
> be removed.
> 
> Signed-off-by: Alexey Marchuk <alexeymar@mellanox.com>
> Signed-off-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
> ---
>  drivers/common/mlx5/linux/meson.build | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/common/mlx5/linux/meson.build b/drivers/common/mlx5/linux/meson.build
> index cdee40c553..f3b8e5741b 100644
> --- a/drivers/common/mlx5/linux/meson.build
> +++ b/drivers/common/mlx5/linux/meson.build
> @@ -209,7 +209,11 @@ if  libmtcr_ul_found
>  endif
>  
>  foreach arg:has_sym_args
> -    mlx5_config.set(arg[0], cc.has_header_symbol(arg[1], arg[2], dependencies: libs, args: cflags))
> +    file_prefix = '#pragma clang diagnostic ignored "-Wunused-value"'
> +    cflags += [
> +            '-Wno-pedantic',
> +    ]
> +    mlx5_config.set(arg[0], cc.has_header_symbol(arg[1], arg[2], prefix : file_prefix, dependencies: libs, args: cflags))
>  endforeach
>  foreach arg:has_member_args
>      file_prefix = '#include <' + arg[1] + '>'

NAK
This adds more complexity to already overly complex meson build for mlx5.