Re: [dpdk-dev] [PATCH] test-pmd: Fix pointer aliasing error

[Olivier MATZ <olivier.matz@6wind.com>]

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