On Saturday 18 January 2014 14:03:26 Antonio Quartulli wrote: > On 18/01/14 12:31, Chen Gang wrote: > > Unfortunately, not all compilers assumes the structures within a pack > > region also need be packed (e.g. metag), so need add a pack explicitly > > to satisfy all compilers. > > > > The related error (under metag with allmodconfig): > > MODPOST 2952 modules > > > > ERROR: "__compiletime_assert_431" [net/batman-adv/batman-adv.ko] > > undefined! > > ERROR: "__compiletime_assert_432" [net/batman-adv/batman-adv.ko] > > undefined! > > ERROR: "__compiletime_assert_429" [net/batman-adv/batman-adv.ko] > > undefined! > > ERROR: "__compiletime_assert_428" [net/batman-adv/batman-adv.ko] > > undefined! > > ERROR: "__compiletime_assert_423" [net/batman-adv/batman-adv.ko] > > undefined! > > > > Signed-off-by: Chen Gang <gang.chen.5i5j@xxxxxxxxx> > > David, what do you think about this change? > > > Can "__packed __aligned(2)" generate a different structure padding than > "#pragma pack(2)" ? > > I am not really sure about the difference between the two. But if we > have the possibility that the padding may change then this patch should > go into net, otherwise we will have a protocol compatibility problem > between 3.13 and 3.14. (Chen: sorry I didn't twig what you were referring to before about #pragma pack not working) 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__). 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. Cheers James
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