Re: [PATCH linux-next] net: batman-adv: use "__packed __aligned(2)" for each structure instead of "__packed(2)" region

[Chen Gang <gang.chen.5i5j@gmail.com>]

On 01/19/2014 05:30 PM, Antonio Quartulli wrote:
> On 19/01/14 02:10, James Hogan wrote:
>>
>> It appears that the following gcc patch adds support for #pragma pack:
>> http://gcc.gnu.org/ml/gcc-patches/2006-10/msg01115.html
>>
>> I gave it a quick spin on metag gcc (which is unfortunately stuck on an old 
>> version) and it seems to fix my simple test case so that #pragma pack(2) 
>> becomes equivalent to __packed __aligned(2) (for sizeof and __alignof__).
>>
> 
> Then I personally think that it is better to fix metag gcc instead of
> changing the kernel.
> 
> Actually there are many different spots where "#pragma pack" is used.
> batman-adv is just the only one having compile time checks for structure
> sizes.
> 

What Antonio said sounds reasonable to me.

>>
>> However, the __packed and __aligned are linux specific macros to abstract 
>> compiler details, whereas #pragma pack appears to be a compiler-specific WIN32 
>> style equivalent to GCC's __attribute__((packed)) and 
>> __attribute__((aligned(2))) (these are what __packed and __aligned use in 
>> compiler-gcc.h).
>>
>> Therefore I believe using the Linux abstractions is still more correct here.
> 
> If you really think so, I'd suggest to grep in the kernel and catch all
> the other occurrences of "#pragma pack" and change them all (assuming
> that using __attribute__((aligned(2))) is the way to go).
> 


Thanks.
-- 
Chen Gang

Open, share and attitude like air, water and life which God blessed