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From: Olivier Matz <olivier.matz@6wind.com>
To: Eli Britstein <elibr@nvidia.com>
Cc: dev@dpdk.org, Ilya Maximets <i.maximets@ovn.org>,
	Gaetan Rivet <gaetanr@nvidia.com>, Majd Dibbiny <majd@nvidia.com>,
	Asaf Penso <asafp@nvidia.com>,
	Thomas Monjalon <thomas@monjalon.net>,
	Harry Van Haaren <harry.van.haaren@intel.com>,
	stable@dpdk.org
Subject: Re: [dpdk-dev] [PATCH 2/3] mbuf: avoid cast-align warning in pktmbuf mtod offset macro
Date: Wed, 28 Jul 2021 17:28:47 +0200	[thread overview]
Message-ID: <YQF3rxG8y3cEz13L@platinum> (raw)
In-Reply-To: <20210713064910.12793-3-elibr@nvidia.com>

On Tue, Jul 13, 2021 at 09:49:09AM +0300, Eli Britstein wrote:
> In rte_pktmbuf_mtod_offset macro, there is a casting from char * to type
> 't', which may cause cast-align warning when using gcc flags
> '-Werror -Wcast-align':
> 
> .../include/rte_mbuf_core.h:723:3: error: cast increases required alignment
>     of target type [-Werror=cast-align]
>   723 |  ((t)((char *)(m)->buf_addr + (m)->data_off + (o)))
>       |   ^
> 
> As the code assumes correct alignment, add first a (void *) casting, to
> avoid the warning.
> 
> Fixes: af75078fece3 ("first public release")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Eli Britstein <elibr@nvidia.com>

My initial thinking was that it's the problem of the application: if
-Werror=cast-align is used, it is up to the application to cast the
return value of rte_pktmbuf_mtod_offset() to (void *) before casting it
to the network type.

But, if I understand correctly, the problem is not about the application
code itself, but about inlined code in the header files of dpdk
(i.e. compiling an empty C file that just includes the dpdk headers with
-Werror=cast-align). Is it correct? If yes I think it should be
highlighted in the commit log.

Out of curiosity, how did you find the errors? I mean, is it possible
that some casts are missing some other headers, or is this patchset
exhaustive?

Thanks,
Olivier


> ---
>  lib/mbuf/rte_mbuf_core.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/mbuf/rte_mbuf_core.h b/lib/mbuf/rte_mbuf_core.h
> index bb38d7f581..dabdeee604 100644
> --- a/lib/mbuf/rte_mbuf_core.h
> +++ b/lib/mbuf/rte_mbuf_core.h
> @@ -720,7 +720,7 @@ struct rte_mbuf_ext_shared_info {
>   *   The type to cast the result into.
>   */
>  #define rte_pktmbuf_mtod_offset(m, t, o)	\
> -	((t)((char *)(m)->buf_addr + (m)->data_off + (o)))
> +	((t)(void *)((char *)(m)->buf_addr + (m)->data_off + (o)))
>  
>  /**
>   * A macro that points to the start of the data in the mbuf.
> -- 
> 2.28.0.2311.g225365fb51
> 

  parent reply	other threads:[~2021-07-28 15:28 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-13  6:49 [dpdk-dev] [PATCH 0/3] Avoid cast-align warnings Eli Britstein
2021-07-13  6:49 ` [dpdk-dev] [PATCH 1/3] net: avoid cast-align warning in VLAN insert function Eli Britstein
2021-07-30 10:57   ` Olivier Matz
2021-07-13  6:49 ` [dpdk-dev] [PATCH 2/3] mbuf: avoid cast-align warning in pktmbuf mtod offset macro Eli Britstein
2021-07-13  7:43   ` Thomas Monjalon
2021-07-28 15:28   ` Olivier Matz [this message]
2021-07-29  7:13     ` Eli Britstein
2021-07-30 11:10       ` Olivier Matz
2021-08-01  8:06         ` Eli Britstein
2021-10-19  6:41           ` Eli Britstein
2021-10-19  9:47             ` Olivier Matz
2021-07-13  6:49 ` [dpdk-dev] [PATCH 3/3] eal/x86: avoid cast-align warning in x86 memcpy functions Eli Britstein
2021-10-21  8:51 ` [dpdk-dev] [PATCH V2 1/3] net: avoid cast-align warning in VLAN insert function Eli Britstein
2021-10-21  8:51   ` [dpdk-dev] [PATCH V2 2/3] mbuf: avoid cast-align warning in pktmbuf mtod offset macro Eli Britstein
2021-10-21  8:51   ` [dpdk-dev] [PATCH V2 3/3] eal/x86: avoid cast-align warning in x86 memcpy functions Eli Britstein
2021-10-25 15:29     ` [dpdk-dev] [dpdk-stable] " Thomas Monjalon
2021-10-21 15:48   ` [dpdk-dev] [PATCH V2 1/3] net: avoid cast-align warning in VLAN insert function Stephen Hemminger
2021-10-21 16:16     ` Eli Britstein
2021-10-21 16:22       ` Stephen Hemminger

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