From mboxrd@z Thu Jan 1 00:00:00 1970 From: Adrien Mazarguil Subject: Re: [PATCH] net/mlx5: fix linkage error for glue lib Date: Wed, 25 Jul 2018 11:24:47 +0200 Message-ID: <20180725092447.GW5211@6wind.com> References: <20180724085445.52206-1-shahafs@mellanox.com> <20180724120048.GQ5211@6wind.com> <20180724120551.GR5211@6wind.com> <20180724160346.GU5211@6wind.com> <470558cc469c49f9b5c6454b5b6c54c0@XCH-ALN-002.cisco.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: Shahaf Shuler , Yongseok Koh , "dev@dpdk.org" , "stable@dpdk.org" , =?utf-8?B?TsOpbGlv?= Laranjeiro , "Hanoch Haim (hhaim)" To: "Yaroslav Brustinov (ybrustin)" Return-path: Received: from mail-wm0-f67.google.com (mail-wm0-f67.google.com [74.125.82.67]) by dpdk.org (Postfix) with ESMTP id AC9F0F72 for ; Wed, 25 Jul 2018 11:25:04 +0200 (CEST) Received: by mail-wm0-f67.google.com with SMTP id s14-v6so5287453wmc.1 for ; Wed, 25 Jul 2018 02:25:04 -0700 (PDT) Content-Disposition: inline In-Reply-To: <470558cc469c49f9b5c6454b5b6c54c0@XCH-ALN-002.cisco.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Wed, Jul 25, 2018 at 07:38:39AM +0000, Yaroslav Brustinov (ybrustin) wrote: > +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. OK, let's forget max_align_t. Even better, how about alignas(RTE_CACHE_LINE_SIZE) just in case the same GCC version complains about the lack of a 128 byte alignment on architectures like IBM POWER8. (remember to #include for RTE_CACHE_LINE_SIZE) > -----Original Message----- > From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com] > Sent: Tuesday, July 24, 2018 19:04 > To: Yaroslav Brustinov (ybrustin) > Cc: Shahaf Shuler ; Yongseok Koh ; dev@dpdk.org; stable@dpdk.org; Nélio Laranjeiro > 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 > #include > #include > > [...] > > +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 > > Cc: Yongseok Koh ; dev@dpdk.org; Yaroslav > > Brustinov (ybrustin) ; stable@dpdk.org; Nélio > > Laranjeiro > > 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 > > > > #include > > > > > > > > [...] > > > > 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 -- Adrien Mazarguil 6WIND