On Wed, Jun 15, 2016 at 10:51:27PM +0300, Yury Norov wrote:
> Hi Madhavan,
>
> On Wed, Jun 15, 2016 at 05:12:53PM +0530, Madhavan Srinivasan wrote:
> > When decoding the perf_regs mask in regs_dump__printf(),
> > we loop through the mask using find_first_bit and find_next_bit functions.
> > And mask is of type "u64". But "u64" is send as a "unsigned long *" to
> > lib functions along with sizeof().
> >
> > While the exisitng code works fine in most of the case, when using a 32bit
> > perf
> > on a 64bit kernel (Big Endian), we end reading the wrong word. In
> > find_first_bit(),
> > one word at a time (based on BITS_PER_LONG) is loaded and
> > checked for any bit set. In 32bit BE userspace,
> > BITS_PER_LONG turns out to be 32, and for a mask value of
> > "0x00000000000000ff", find_first_bit will return 32, instead of 0.
> > Reason for this is that, value in the word0 is all zeros and value
> > in word1 is 0xff. Ideally, second word in the mask should be loaded
> > and searched. Patch swaps the word to look incase of 32bit BE.
>
> I think this is not a problem of find_bit() at all. You have wrong
> typecast as the source of problem (tools/perf/util/session.c"):
>
> 940 static void regs_dump__printf(u64 mask, u64 *regs)
> 941 {
> 942 unsigned rid, i = 0;
> 943
> 944 for_each_set_bit(rid, (unsigned long *) &mask, sizeof(mask) * 8) {
> ^^^^ Here ^^^^
> 945 u64 val = regs[i++];
> 946
> 947 printf(".... %-5s 0x%" PRIx64 "\n",
> 948 perf_reg_name(rid), val);
> 949 }
> 950 }
>
> But for some reason you change correct find_bit()...
>
> Though proper fix is like this for me:
>
> static void regs_dump__printf(u64 mask, u64 *regs)
> {
> unsigned rid, i = 0;
> unsigned long _mask[sizeof(mask)/sizeof(unsigned long)];
>
> _mask[0] = mask & ULONG_MAX;
> if (sizeof(mask) > sizeof(unsigned long))
> _mask[1] = mask >> BITS_PER_LONG;
>
> for_each_set_bit(rid, _mask, sizeof(mask) * BITS_PER_BYTE) {
> u64 val = regs[i++];
>
> printf(".... %-5s 0x%" PRIx64 "\n",
> perf_reg_name(rid), val);
> }
> }
>
> Maybe there already is some macro doing the conversion for you...
yes it is, cpu_to_le64() is what you want
>
> Yury.
>
> > Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
> > Cc: Adrian Hunter <adrian.hun...@intel.com>
> > Cc: Borislav Petkov <b...@suse.de>
> > Cc: David Ahern <dsah...@gmail.com>
> > Cc: George Spelvin <li...@horizon.com>
> > Cc: Jiri Olsa <jo...@redhat.com>
> > Cc: Namhyung Kim <namhy...@kernel.org>
> > Cc: Rasmus Villemoes <li...@rasmusvillemoes.dk>
> > Cc: Wang Nan <wangn...@huawei.com>
> > Cc: Yury Norov <yury.no...@gmail.com>
> > Cc: Michael Ellerman <m...@ellerman.id.au>
> > Signed-off-by: Madhavan Srinivasan <ma...@linux.vnet.ibm.com>
> > ---
> > tools/lib/find_bit.c | 17 +++++++++++++++++
> > 1 file changed, 17 insertions(+)
> >
> > diff --git a/tools/lib/find_bit.c b/tools/lib/find_bit.c
> > index 9122a9e80046..996b3e04324f 100644
> > --- a/tools/lib/find_bit.c
> > +++ b/tools/lib/find_bit.c
> > @@ -37,7 +37,12 @@ static unsigned long _find_next_bit(const unsigned long
> > *addr,
> > if (!nbits || start >= nbits)
> > return nbits;
> >
> > +#if (__BYTE_ORDER == __BIG_ENDIAN) && (BITS_PER_LONG != 64)
> > + tmp = addr[(((nbits - 1)/BITS_PER_LONG) - (start / BITS_PER_LONG))]
> > + ^ invert;
> > +#else
> > tmp = addr[start / BITS_PER_LONG] ^ invert;
> > +#endif
> >
> > /* Handle 1st word. */
> > tmp &= BITMAP_FIRST_WORD_MASK(start);
> > @@ -48,7 +53,12 @@ static unsigned long _find_next_bit(const unsigned long
> > *addr,
> > if (start >= nbits)
> > return nbits;
> >
> > +#if (__BYTE_ORDER == __BIG_ENDIAN) && (BITS_PER_LONG != 64)
> > + tmp = addr[(((nbits - 1)/BITS_PER_LONG) - (start /
> > BITS_PER_LONG))]
> > + ^ invert;
> > +#else
> > tmp = addr[start / BITS_PER_LONG] ^ invert;
> > +#endif
> > }
> >
> > return min(start + __ffs(tmp), nbits);
> > @@ -75,8 +85,15 @@ unsigned long find_first_bit(const unsigned long *addr,
> > unsigned long size)
> > unsigned long idx;
> >
> > for (idx = 0; idx * BITS_PER_LONG < size; idx++) {
> > +#if (__BYTE_ORDER == __BIG_ENDIAN) && (BITS_PER_LONG != 64)
> > + if (addr[(((size-1)/BITS_PER_LONG) - idx)])
> > + return min(idx * BITS_PER_LONG +
> > + __ffs(addr[(((size-1)/BITS_PER_LONG) - idx)]),
> > + size);
> > +#else
> > if (addr[idx])
> > return min(idx * BITS_PER_LONG + __ffs(addr[idx]),
> > size);
> > +#endif
> > }
> >
> > return size;
> > --
> > 1.9.1
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