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    SubjectRe: [PATCH 1/3] arch/x86: Use offsetof
    Hi!

    > From: Julia Lawall <julia@diku.dk>
    >
    > In the patch cc154ac64aa8d3396b187f64cef01ce67f433324, Al Viro observed
    > that the proper way to compute the distance between two structure fields is
    > to use offsetof() or a cast to a pointer to character. The same change can
    > be applied to a few more files.
    >
    > The change was made using the following semantic patch
    > (http://www.emn.fr/x-info/coccinelle/)
    >
    > // <smpl>
    > @r@
    > type T;
    > T s;
    > type T1, T2;
    > identifier fld1, fld2;
    > typedef uint8_t;
    > typedef u8;
    > @@
    >
    > (
    > (char *)&s.fld1 - (char *)&s.fld2
    > |
    > (uint8_t *)&s.fld1 - (uint8_t *)&s.fld2
    > |
    > (u8 *)&s.fld1 - (u8 *)&s.fld2
    > |
    > - (T1)&s.fld1 - (T2)&s.fld2
    > + offsetof(T,fld1) - offsetof(T,fld2)
    > )
    > // </smpl>
    >
    > Signed-off-by: Julia Lawall <julia@diku.dk>
    > ---
    >
    > diff -u -p a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
    > --- a/arch/x86/kernel/vm86_32.c 2007-10-22 11:25:00.000000000 +0200
    > +++ b/arch/x86/kernel/vm86_32.c 2007-12-26 16:27:15.000000000 +0100
    > @@ -215,7 +215,9 @@ asmlinkage int sys_vm86old(struct pt_reg
    > ret = -EFAULT;
    > if (tmp)
    > goto out;
    > - memset(&info.vm86plus, 0, (int)&info.regs32 - (int)&info.vm86plus);
    > + memset(&info.vm86plus, 0,
    > + offsetof(struct kernel_vm86_struct, regs32) -
    > + offsetof(struct kernel_vm86_struct, vm86plus));

    I do not think this makes it more readable... (int) -> (char *) would
    make it portable and readable, AFAICT.
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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