From: Eli Britstein <elibr@nvidia.com>
To: Olivier Matz <olivier.matz@6wind.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: Thu, 29 Jul 2021 10:13:45 +0300 [thread overview]
Message-ID: <045f7d4b-c9dc-0a1e-25c8-359f14dfcc66@nvidia.com> (raw)
In-Reply-To: <YQF3rxG8y3cEz13L@platinum>
On 7/28/2021 6:28 PM, Olivier Matz wrote:
> External email: Use caution opening links or attachments
>
>
> 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.
I think yes, though in this specific patch it is not even an inline
function, but a macro.
However, I don't have a synthetic application example to show those
warnings, thus didn't put such in the commit msg.
>
> 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?
Currently OVS-DPDK is compiled only with -Wno-cast-align.
Following complaint that a recent commit introduced a degradation in OVS
[1], I compiled OVS without this warning deprecation.
The fixes in OVS are [2] and [3] (already merged). The fixes in DPDK are
in this patch-set.
[1] https://mail.openvswitch.org/pipermail/ovs-dev/2021-July/385084.html
[2] https://mail.openvswitch.org/pipermail/ovs-dev/2021-July/386278.html
e8cccd3a3589 ("netdev-offload-dpdk: Fix IPv6 rewrite cast-align
warning.")
[3] https://mail.openvswitch.org/pipermail/ovs-dev/2021-July/386279.html
1f7f557603a5 ("netdev-offload-dpdk: Fix vxlan vni cast-align
warnings.")
> 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
>>
next prev parent reply other threads:[~2021-07-29 7:13 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
2021-07-29 7:13 ` Eli Britstein [this message]
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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