From: "Yaroslav Brustinov (ybrustin)" <ybrustin@cisco.com>
To: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Cc: "Shahaf Shuler" <shahafs@mellanox.com>,
"Yongseok Koh" <yskoh@mellanox.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"stable@dpdk.org" <stable@dpdk.org>,
"Nélio Laranjeiro" <nelio.laranjeiro@6wind.com>,
"Hanoch Haim (hhaim)" <hhaim@cisco.com>
Subject: Re: [dpdk-stable] [PATCH] net/mlx5: fix linkage error for glue lib
Date: Wed, 25 Jul 2018 07:38:39 +0000 [thread overview]
Message-ID: <470558cc469c49f9b5c6454b5b6c54c0@XCH-ALN-002.cisco.com> (raw)
In-Reply-To: <20180724160346.GU5211@6wind.com>
+Hanoch
I've added -std=c11 flag to our compilation to check.
Without alignas(max_align_t):
/usr/bin/ld: Warning: alignment 8 of symbol `mlx5_glue' in src/dpdk/drivers/net/mlx5/mlx5_glue.c.11.o is smaller than 32 in src/dpdk/drivers/net/mlx5/mlx5_rxq.c.11.o
With alignas(max_align_t):
/usr/bin/ld: Warning: alignment 16 of symbol `mlx5_glue' in src/dpdk/drivers/net/mlx5/mlx5_glue.c.11.o is smaller than 32 in src/dpdk/drivers/net/mlx5/mlx5_rxq.c.11.o
Using alignas(64) does not produce linker warning.
Thanks,
Yaroslav.
-----Original Message-----
From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
Sent: Tuesday, July 24, 2018 19:04
To: Yaroslav Brustinov (ybrustin) <ybrustin@cisco.com>
Cc: Shahaf Shuler <shahafs@mellanox.com>; Yongseok Koh <yskoh@mellanox.com>; dev@dpdk.org; stable@dpdk.org; Nélio Laranjeiro <nelio.laranjeiro@6wind.com>
Subject: Re: [PATCH] net/mlx5: fix linkage error for glue lib
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:shahafs@mellanox.com]
> Sent: Tuesday, July 24, 2018 16:51
> To: Adrien Mazarguil <adrien.mazarguil@6wind.com>
> Cc: Yongseok Koh <yskoh@mellanox.com>; dev@dpdk.org; Yaroslav
> Brustinov (ybrustin) <ybrustin@cisco.com>; stable@dpdk.org; Nélio
> Laranjeiro <nelio.laranjeiro@6wind.com>
> 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
next prev parent reply other threads:[~2018-07-25 7:38 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-24 8:54 Shahaf Shuler
2018-07-24 12:00 ` Adrien Mazarguil
2018-07-24 12:05 ` Adrien Mazarguil
2018-07-24 13:51 ` Shahaf Shuler
2018-07-24 14:24 ` Yaroslav Brustinov (ybrustin)
2018-07-24 16:03 ` Adrien Mazarguil
2018-07-25 7:38 ` Yaroslav Brustinov (ybrustin) [this message]
2018-07-25 9:24 ` Adrien Mazarguil
2018-07-25 10:02 ` Yaroslav Brustinov (ybrustin)
2018-07-25 13:18 ` [dpdk-stable] [PATCH v2] " Shahaf Shuler
2018-07-25 13:22 ` Adrien Mazarguil
2018-07-26 5:44 ` Shahaf Shuler
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