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From: "Qiu, Michael" <michael.qiu@intel.com>
To: "Richardson, Bruce" <bruce.richardson@intel.com>
Thread-Topic: [PATCH] test-pmd: Fix pointer aliasing error
Thread-Index: AQHQDuxQX/2B2GdrV0OV5lPAliaykw==
Date: Wed, 3 Dec 2014 15:19:34 +0000
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Cc: "dev@dpdk.org" <dev@dpdk.org>, Michael Qiu <qdy220091330@gmail.com>
Subject: Re: [dpdk-dev] [PATCH] test-pmd: Fix pointer aliasing error
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X-List-Received-Date: Wed, 03 Dec 2014 19:44:43 -0000
On 2014/12/3 22:51, Richardson, Bruce wrote:=0A=
> On Wed, Dec 03, 2014 at 01:59:58PM +0000, Qiu, Michael wrote:=0A=
>> On 2014/12/3 19:43, Richardson, Bruce wrote:=0A=
>>> On Wed, Dec 03, 2014 at 07:28:19PM +0800, Michael Qiu wrote:=0A=
>>>> app/test-pmd/csumonly.c: In function =91get_psd_sum=92:=0A=
>>>> build/include/rte_ip.h:161: error: dereferencing pointer =91u16=92=0A=
>>>> does break strict-aliasing rules=0A=
>>>> build/include/rte_ip.h:157: note: initialized from here=0A=
>>>> ...=0A=
>>>>=0A=
>>>> The root cause is that, compile enable strict aliasing by default,=0A=
>>>> while in function rte_raw_cksum() try to convert 'const char *'=0A=
>>>> to 'const uint16_t *'.=0A=
>>>>=0A=
>>> What compiler version is this with? Is there any other way to fix this=
=0A=
>>> other than disabling the compiler warnings. Turning off strict aliasing=
may=0A=
>>> affect performance as it reduces the number of optimizations that the c=
ompiler=0A=
>>> can perform.=0A=
>> The compile version is:=0A=
>>=0A=
>> $ gcc -v=0A=
>> Using built-in specs.=0A=
>> Target: x86_64-redhat-linux=0A=
>> ...=0A=
>> gcc version 4.4.7 20120313 (Red Hat 4.4.7-4) (GCC)=0A=
>>=0A=
>>=0A=
>> The OS is centos6.5 x86_64=0A=
>>=0A=
>>=0A=
>> Actually, another possible solution is, as gcc manual shows, use union.=
=0A=
>> In function rte_raw_cksum() of lib/librte_net/rte_ip.h:=0A=
>>=0A=
>> static inline uint16_t=0A=
>> rte_raw_cksum(const char *buf, size_t len){=0A=
>> union {=0A=
>> const char *ubuf;=0A=
>> const uint16_t *uu16;=0A=
>> } convert;=0A=
>>=0A=
>> convert.ubuf =3D buf;=0A=
>> const uint16_t *u16 =3D convert.uu16;=0A=
>> ...=0A=
>> }=0A=
>>=0A=
>> This may be work, but not test yet.=0A=
>>=0A=
>> Any comments about this solution?=0A=
> what happens if you make rte_raw_cksum take a void * (or const void *) pa=
rameter=0A=
> instead of "const char *"?=0A=
=0A=
"size_t len" is for type char, it is the the array size(for char array=0A=
is byte numbers), if we use void *, the meaning maybe confuse I think.=0A=
But it should work with other code change.=0A=
=0A=
Thanks,=0A=
Michael=0A=
>=0A=
> /Bruce=0A=
>=0A=
=0A=