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From: "Qiu, Michael" <michael.qiu@intel.com>
To: Michael Qiu <qdy220091330@gmail.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"Thomas.monjalon@6wind.com" <thomas.monjalon@6wind.com>
Subject: Re: [dpdk-dev] [PATCH v3] test-pmd: Fix pointer aliasing error
Date: Wed, 10 Dec 2014 03:44:25 +0000
Message-ID: <533710CFB86FA344BFBF2D6802E60286C9E52D@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <533710CFB86FA344BFBF2D6802E60286C9D683@SHSMSX101.ccr.corp.intel.com>

Hi Thomas,

What's going on with this patch?

I really do not have other better solution.

Thanks,
Michael
On 12/8/2014 9:30 AM, Qiu, Michael wrote:
> On 12/4/2014 9:35 PM, 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 *'.
>>
>> This patch is one workaround fix.
>>
>> Signed-off-by: Michael Qiu <michael.qiu@intel.com>
>> ---
>> v3 --> v2:
>> 	use uintptr_t instead of unsigned long to
>> 	save pointer.
>>
>> v2 --> v1:
>> 	Workaround solution instead of shut off the
>> 	gcc params.
>>
>>  lib/librte_net/rte_ip.h | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
>> index 61e4457..cda3436 100644
>> --- a/lib/librte_net/rte_ip.h
>> +++ b/lib/librte_net/rte_ip.h
>> @@ -154,7 +154,8 @@ struct ipv4_hdr {
>>  static inline uint16_t
>>  rte_raw_cksum(const char *buf, size_t len)
>>  {
>> -	const uint16_t *u16 = (const uint16_t *)buf;
>> +	uintptr_t ptr = (uintptr_t)buf;
>> +	const uint16_t *u16 = (const uint16_t *)ptr;
>>  	uint32_t sum = 0;
>>  
>>  	while (len >= (sizeof(*u16) * 4)) {
> This workaround is to solve the compile issue of GCC strict-aliasing(Two
> different type pointers should not be point to the same memory address).
>
> For GCC 4.4.7 it will definitely occurs if  flags "-fstrict-aliasing"
> and "-Wall" used.
>
> Thanks,
> Michael
>


  reply	other threads:[~2014-12-10  3:44 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   ` [dpdk-dev] [PATCH] " 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 [this message]
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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