On Tue, Jun 21, 2016 at 06:35:31PM +0300, Yury Norov wrote:
SNIP
> > index 5214974e841a..1337b1c73f82 100644
> > --- a/tools/perf/util/session.c
> > +++ b/tools/perf/util/session.c
> > @@ -940,8 +940,22 @@ static void branch_stack__printf(struct perf_sample
> > *sample)
> > static void regs_dump__printf(u64 mask, u64 *regs)
> > {
> > unsigned rid, i = 0;
> > + unsigned long _mask[sizeof(mask)/sizeof(unsigned long)];
> >
> > - for_each_set_bit(rid, (unsigned long *) &mask, sizeof(mask) * 8) {
> > + /*
> > + * Since u64 is passed as 'unsigned long *', check
> > + * to see whether we need to swap words within u64.
> > + * Reason being, in 32 bit big endian userspace on a
> > + * 64bit kernel, 'unsigned long' is 32 bits.
> > + * When reading u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1],
> > + * we will get wrong value for the mask. This is what
> > + * find_first_bit() and find_next_bit() is doing.
> > + * Issue here is "(u32 *)(&val)[0]" gets upper 32 bits of u64,
> > + * but perf assumes it gets lower 32bits of u64. Hence the check
> > + * and swap.
> > + */
>
> Identical comments... I'd prefer to see it in commit message, or
> better in function description. For me it's pretty straightforward in
> understanding what happens here in-place without comments.
yep, please use this just once as the fucntion description
thanks,
jirka
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