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

From: Chen Gang
Date: Sun Jan 19 2014 - 04:52:06 EST

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:
>> 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).

Chen Gang

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