Re: [PATCH] net/mlx5: fix linkage error for glue lib

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

On Tue, Jul 24, 2018 at 11:54:45AM +0300, Shahaf Shuler wrote:
> From: Yaroslav Brustinov <ybrustin@cisco.com>
> 
> Compiling with gcc 4.7.2 introduced the linkage error
> 
> "bin/ld: Warning: alignment 8 of symbol `mlx5_glue' in
> src/dpdk/drivers/net/mlx5/mlx5_glue.c.21.o is smaller than 16 in
> src/dpdk/drivers/net/mlx5/mlx5_rxq.c.21.o"
> 
> Fix it be forcing the alignment of the glue lib.
> 
> Fixes: 0e83b8e536c1 ("net/mlx5: move rdma-core calls to separate file")
> Cc: stable@dpdk.org
> Cc: nelio.laranjeiro@6wind.com
> Cc: adrien.mazarguil@6wind.com
> 
> Signed-off-by: Yaroslav Brustinov <ybrustin@cisco.com>
> Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>

Odd, how could this happen assuming both files are compiled during the same
run using identical flags? Looks like a compiler issue.

Anyway, may I suggest an alignment constraint on the structure type in
mlx5_glue.h instead, so that all users inherit it. E.g. using C11 syntax:

 #include <stdalign.h>
 #include <stddef.h>

 [...]
 alignas(max_align_t)
 struct mlx5_glue {
     [...]
 };

> ---
>  drivers/net/mlx5/mlx5_glue.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/mlx5/mlx5_glue.c b/drivers/net/mlx5/mlx5_glue.c
> index c7965e51fe..c56c69bb13 100644
> --- a/drivers/net/mlx5/mlx5_glue.c
> +++ b/drivers/net/mlx5/mlx5_glue.c
> @@ -343,7 +343,9 @@ mlx5_glue_dv_create_qp(struct ibv_context *context,
>  #endif
>  }
>  
> -const struct mlx5_glue *mlx5_glue = &(const struct mlx5_glue){
> +const struct mlx5_glue *mlx5_glue __attribute__((__aligned__(64))) =
> +						&(const struct mlx5_glue)
> +{
>  	.version = MLX5_GLUE_VERSION,
>  	.fork_init = mlx5_glue_fork_init,
>  	.alloc_pd = mlx5_glue_alloc_pd,
> -- 
> 2.12.0
> 

-- 
Adrien Mazarguil
6WIND