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From: "Qiu, Michael" <michael.qiu@intel.com>
To: "Richardson, Bruce" <bruce.richardson@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>, Michael Qiu <qdy220091330@gmail.com>
Subject: Re: [dpdk-dev] [PATCH] test-pmd: Fix pointer aliasing error
Date: Wed, 3 Dec 2014 15:19:34 +0000
Message-ID: <533710CFB86FA344BFBF2D6802E60286C9C5BA@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <20141203145148.GB2396@bricha3-MOBL3>

On 2014/12/3 22:51, Richardson, Bruce wrote:
> On Wed, Dec 03, 2014 at 01:59:58PM +0000, Qiu, Michael wrote:
>> On 2014/12/3 19:43, Richardson, Bruce wrote:
>>> On Wed, Dec 03, 2014 at 07:28:19PM +0800, Michael Qiu wrote:
>>>> app/test-pmd/csumonly.c: In function ‘get_psd_sum’:
>>>> build/include/rte_ip.h:161: error: dereferencing pointer ‘u16’
>>>> 	does break strict-aliasing rules
>>>> build/include/rte_ip.h:157: note: initialized from here
>>>> 	...
>>>>
>>>> The root cause is that, compile enable strict aliasing by default,
>>>> while in function rte_raw_cksum() try to convert 'const char *'
>>>> to 'const uint16_t *'.
>>>>
>>> What compiler version is this with? Is there any other way to fix this
>>> other than disabling the compiler warnings. Turning off strict aliasing may
>>> affect performance as it reduces the number of optimizations that the compiler
>>> can perform.
>> The compile version is:
>>
>> $ gcc -v
>> Using built-in specs.
>> Target: x86_64-redhat-linux
>> ...
>> gcc version 4.4.7 20120313 (Red Hat 4.4.7-4) (GCC)
>>
>>
>> The OS is centos6.5 x86_64
>>
>>
>> Actually, another possible solution is, as gcc manual shows, use union.
>> In function rte_raw_cksum() of lib/librte_net/rte_ip.h:
>>
>> static inline uint16_t
>> rte_raw_cksum(const char *buf, size_t len){
>>     union {
>>         const char *ubuf;
>>         const uint16_t *uu16;
>>     } convert;
>>
>>     convert.ubuf = buf;
>>     const uint16_t *u16 = convert.uu16;
>>     ...
>> }
>>
>> This may be work, but not test yet.
>>
>> Any comments about this solution?
> what happens if you make rte_raw_cksum take a void * (or const void *) parameter
> instead of "const char *"?

"size_t len" is for type char, it is the the array size(for char array
is byte numbers), if we use void *, the meaning maybe confuse I think.
But it should work with other code change.

Thanks,
Michael
>
> /Bruce
>


  reply	other threads:[~2014-12-03 19:44 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1417606044-3432-1-git-send-email-michael.qiu@intel.com>
     [not found] ` <1417606099-3489-1-git-send-email-michael.qiu@intel.com>
2014-12-03 11:42   ` Bruce Richardson
2014-12-03 13:59     ` Qiu, Michael
2014-12-03 14:51       ` Bruce Richardson
2014-12-03 15:19         ` Qiu, Michael [this message]
2014-12-03 15:36           ` Bruce Richardson
2014-12-04  2:38             ` Qiu, Michael
2014-12-04  3:28               ` [dpdk-dev] [PATCH v2] " Michael Qiu
2014-12-04  4:16                 ` [dpdk-dev] [PATCH v3] " Michael Qiu
2014-12-05  5:34                   ` Qiu, Michael
2014-12-05  9:24                     ` Thomas Monjalon
2014-12-08  1:28                       ` Qiu, Michael
2014-12-08  1:30                   ` Qiu, Michael
2014-12-10  3:44                     ` Qiu, Michael
2014-12-11  0:54                     ` Thomas Monjalon
2014-12-11 17:51                       ` r k
2014-12-12  6:49                         ` Qiu, Michael
2014-12-04 12:54                 ` [dpdk-dev] [PATCH v2] " Ananyev, Konstantin
2014-12-03 15:24     ` [dpdk-dev] [PATCH] " Olivier MATZ
2014-12-03 16:03       ` Dayu Qiu
2014-12-03 15:57     ` Dayu Qiu
2014-12-03 16:26 ` [dpdk-dev] [PATCH] test-pmd: Fix "__BYTE_ORDER__" not defined error Qiu, Michael
2014-12-03 19:59   ` Thomas Monjalon
2014-12-03 20:47     ` [dpdk-dev] [PATCH 0/2] fix endianness in EAL Thomas Monjalon
2014-12-03 20:47       ` [dpdk-dev] [PATCH 1/2] eal: detect endianness Thomas Monjalon
2014-12-04  2:28         ` Qiu, Michael
2014-12-04  9:00           ` Thomas Monjalon
2014-12-04 10:28             ` Qiu, Michael
2014-12-04 12:19               ` Thomas Monjalon
2014-12-04 12:50                 ` Qiu, Michael
2014-12-03 20:47       ` [dpdk-dev] [PATCH 2/2] app/testpmd: fix endianness detection Thomas Monjalon
2014-12-04  9:28       ` [dpdk-dev] [PATCH 0/2] fix endianness in EAL Chao Zhu
2014-12-05 16:01         ` Thomas Monjalon

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