On Tue, Jul 24, 2018 at 02:24:12PM +0000, Yaroslav Brustinov (ybrustin) wrote:
> Hi,
>
> Are you OK with C11?
> I saw in file dpdk/drivers/net/mlx4/mlx4_utils.c:
>
> * C11 code would include stdalign.h and use alignof(max_align_t) however
> * we'll stick with C99 for the time being.
>
> :)
Hah, this code was originally intended to become a generic EAL function
hence the C99 but got rejected. Mellanox PMDs otherwise rely on C11 features
already.
> As far as I understand, the issue is alignment of the pointer itself, not the
> struct.
> I'm not familiar with this command: "alignof(max_align_t)".
> Applying this on the struct:
>
> struct mlx5_glue {
> ...
> } __attribute__((__aligned__(64)));
>
> struct __attribute__((__aligned__(64))) mlx5_glue {
> ...
> };
>
> ...still keeps the linker unhappy.
Right, this was my first (wrong) suggestion that doesn't work on types. How
about the second one instead? Here's how the diff on mlx5_glue.h should look
like:
+#include <stdalign.h>
#include <stddef.h>
#include <stdint.h>
[...]
+alignas(max_align_t)
const struct mlx5_glue *mlx5_glue;
Another comment regarding this patch, commit log should probably mention it
addresses a GCC bug that cannot be reproduced with latter versions. Keep in
mind DPDK recommends to use at least GCC version 4.9.
> -----Original Message-----
> From: Shahaf Shuler [mailto:[email protected]]
> Sent: Tuesday, July 24, 2018 16:51
> To: Adrien Mazarguil <[email protected]>
> Cc: Yongseok Koh <[email protected]>; [email protected]; Yaroslav Brustinov
> (ybrustin) <[email protected]>; [email protected]; Nélio Laranjeiro
> <[email protected]>
> Subject: RE: [PATCH] net/mlx5: fix linkage error for glue lib
>
> Yaroslav,
>
> Tuesday, July 24, 2018 3:06 PM, Adrien Mazarguil:
> > Subject: Re: [PATCH] net/mlx5: fix linkage error for glue lib
> > > 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;
>
> Can you confirm the above suggestion fixes your issue?
>
> >
> > >
--
Adrien Mazarguil
6WIND
