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From: Dayu Qiu <qdy220091330@gmail.com>
To: Olivier MATZ <olivier.matz@6wind.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] test-pmd: Fix pointer aliasing error
Date: Thu, 4 Dec 2014 00:03:42 +0800
Message-ID: <CABW3MVf5pgv3McAn5hO7_4TtvONLA_YQxy-zgLJr9nk5_vF3TQ@mail.gmail.com> (raw)
In-Reply-To: <547F2B37.5060500@6wind.com>

Hi Olivier,

You can check gcc manual.

-fstrict-aliasing
           Allow the compiler to assume the strictest aliasing rules
applicable to the language being
           compiled.  For C (and C++), this activates optimizations based
on the type of expressions.  In
           particular, an object of one type is assumed never to reside at
the same address as an object of a
           different type, unless the types are almost the same.  For
example, an "unsigned int" can alias an
           "int", but not a "void*" or a "double".  A character type may
alias any other type.

So it should not be a bug, but I have no idea about why other version does
not reproduce.

Thanks,
Michael

On Wed, Dec 3, 2014 at 11:24 PM, Olivier MATZ <olivier.matz@6wind.com>
wrote:

> Hi Bruce,
>
> On 12/03/2014 12:42 PM, Bruce Richardson 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.
>>
>
> I can reproduce the issue with a gcc-4.4.6 toolchain. But I think it's
> a toolchain bug as the warning does not occur with other versions I've
> tested.
>
> If it's the case, we could either:
>
> - do nothing: in this case the user need to upgrade its toolchain, or
>   pass the -Wno-strict-aliasing manually in EXTRA_CFLAGS
>
> - add the -Wno-strict-aliasing only for gcc 4.4 in the Makefile
>
> What do you think?
>
> Regards,
> Olivier
>
>


-- 
Thanks & Best Regards
Mike

  reply	other threads:[~2014-12-03 16:03 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
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 [this message]
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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