Messages in this thread | | | Date | Mon, 03 Feb 2014 19:35:24 +0800 | From | Chen Gang <> | Subject | Re: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))" for the related union |
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On 02/03/2014 06:03 PM, Chen Gang wrote: > On 02/03/2014 04:58 PM, Dan Carpenter wrote: >> On Sat, Feb 01, 2014 at 09:57:39PM +0800, Chen Gang wrote: >>> It seems, our kernel still stick to treate 'pack' region have effect >>> with both 'align' and 'sizeof'. >>> >> >> It's not about packed regions. It's about unions. It's saying the >> sizeof() a union is a multiple of 4 unless it's packed. >> >> union foo { >> short x; >> short y; >> }; >> >> The author intended the sizeof(union foo) to be 2 but on metag arch then >> it is 4. >> > > Yeah, just like your original discussion. :-) > > > Hmm... can we say: "for metag compiler, in a pack region, it considers > variables alignment, but does not consider about struct/union alignment > (except append packed to each related struct/union)". > > For compatible (consider about its ABI), it has to keep this features, > but for kernel, it needs be changed. > > So, I suggest to add one parameter to compiler to switch this feature, > and append this parameter to KBUILD_CFLAGS in "arch/metag/Makefile" > which can satisfy both ABI and kernel. >
After append the parameter to KBUILD_CFLAGS in "arch/metag/Makefile",
- I guess/assume "include/uapi/*" should/will not need be modified.
- but need check all files in "arch/metag/include/uapi/*". (add padding data for packed struct/union when __KERNEL__ defined)
- maybe we have to process metag related ABI which not in "*/uapi/*" (add padding data for packed struct/union when __KERNEL__ defined) and when we find them, recommend to move all of them to "*/uapi/*".
Sorry, I don't know whether this way is the best way or not, but for me it is an executable way to solve this feature issue and satisfy both kernel and ABI.
Thanks. -- Chen Gang
Open, share and attitude like air, water and life which God blessed
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