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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: Thu, 4 Dec 2014 02:38:35 +0000
Message-ID: <533710CFB86FA344BFBF2D6802E60286C9C893@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <20141203153634.GA6524@bricha3-MOBL3>

On 12/3/2014 11:36 PM, Richardson, Bruce wrote:
> On Wed, Dec 03, 2014 at 03:19:34PM +0000, Qiu, Michael wrote:
>> 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.
> That shouldn't be a big issue. We can rename it to "size" instead of "len" if
> needed.

As I tested in my env just, void * is still not work, the same errors
post when compile.

Then the solution for DPDK should be:
-  As Olivier suggest, add the -Wno-strict-aliasing only for gcc 4.4 in
the Makefile
- As gcc manual suggest, use "union" to work around this issue.

Thanks,
Michael
>> But it should work with other code change.
>>
>> Thanks,
>> Michael
>>> /Bruce
>>>


  reply	other threads:[~2014-12-04  2:40 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
2014-12-03 15:36           ` Bruce Richardson
2014-12-04  2:38             ` Qiu, Michael [this message]
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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