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...
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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