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

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

On Tue, Jul 24, 2018 at 02:00:48PM +0200, Adrien Mazarguil wrote:
> 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 {
>      [...]
>  };

My bad, this is not a correct use for alignas(), it doesn't work on types.
How about this instead:

 alignas(max_align_t)
 const struct mlx5_glue *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

-- 
Adrien Mazarguil
6WIND