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From: "Qiu, Michael" <michael.qiu@intel.com>
To: "Richardson, Bruce" <bruce.richardson@intel.com>, Michael Qiu
<qdy220091330@gmail.com>
Thread-Topic: [PATCH] test-pmd: Fix pointer aliasing error
Thread-Index: AQHQDuxQX/2B2GdrV0OV5lPAliaykw==
Date: Wed, 3 Dec 2014 13:59:58 +0000
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Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] test-pmd: Fix pointer aliasing error
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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 m=
ay=0A=
> affect performance as it reduces the number of optimizations that the com=
piler=0A=
> can perform.=0A=
=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=
=0A=
Thanks,=0A=
Michael=0A=
>=0A=
> /Bruce=0A=
>=0A=
>> Need to add CFLAG '-Wno-strict-aliasing' to avoid this issue.=0A=
>>=0A=
>> Signed-off-by: Michael Qiu <michael.qiu@intel.com>=0A=
>> ---=0A=
>> app/test-pmd/Makefile | 2 +-=0A=
>> 1 file changed, 1 insertion(+), 1 deletion(-)=0A=
>>=0A=
>> diff --git a/app/test-pmd/Makefile b/app/test-pmd/Makefile=0A=
>> index 97dc2e6..995c874 100644=0A=
>> --- a/app/test-pmd/Makefile=0A=
>> +++ b/app/test-pmd/Makefile=0A=
>> @@ -38,7 +38,7 @@ ifeq ($(CONFIG_RTE_TEST_PMD),y)=0A=
>> #=0A=
>> APP =3D testpmd=0A=
>> =0A=
>> -CFLAGS +=3D -O3=0A=
>> +CFLAGS +=3D -O3 -Wno-strict-aliasing=0A=
>> CFLAGS +=3D $(WERROR_FLAGS)=0A=
>> =0A=
>> ifeq ($(CONFIG_RTE_LIBRTE_PMD_PCAP),y)=0A=
>> -- =0A=
>> 1.9.3=0A=
>>=0A=
=0A=