On Sun, Jul 03, 2016 at 11:31:58PM +0530, Madhavan Srinivasan wrote: > When decoding the perf_regs mask in perf_output_sample_regs(), > we loop through the mask using find_first_bit and find_next_bit functions. > While the exisitng code works fine in most of the case, > the logic is broken for 32bit kernel (Big Endian). > When reading u64 mask using (u32 *)(&val)[0], find_*_bit() assumes it gets > lower 32bits of u64 but instead gets upper 32bits which is wrong. > Proposed fix is to swap the words of the u64 to handle this case. > This is _not_ endianness swap.
In fact, it's broken for 32-bit LE as well if mask is zero and next word on stack is not zero. The rest is OK. Reviewed-by: Yury Norov <yno...@caviumnetworks.com> > > Suggested-by: Yury Norov <yno...@caviumnetworks.com> > Cc: Yury Norov <yno...@caviumnetworks.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Ingo Molnar <mi...@redhat.com> > Cc: Arnaldo Carvalho de Melo <a...@kernel.org> > Cc: Alexander Shishkin <alexander.shish...@linux.intel.com> > Cc: Jiri Olsa <jo...@kernel.org> > Cc: Michael Ellerman <m...@ellerman.id.au> > Signed-off-by: Madhavan Srinivasan <ma...@linux.vnet.ibm.com> > --- > include/linux/bitmap.h | 2 ++ > kernel/events/core.c | 4 +++- > lib/bitmap.c | 19 +++++++++++++++++++ > 3 files changed, 24 insertions(+), 1 deletion(-) > > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h > index e9b0b9ab07e5..d95b422db183 100644 > --- a/include/linux/bitmap.h > +++ b/include/linux/bitmap.h > @@ -188,6 +188,8 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf, > #define small_const_nbits(nbits) \ > (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG) > > +extern void bitmap_from_u64(unsigned long *dst, u64 mask); > + > static inline void bitmap_zero(unsigned long *dst, unsigned int nbits) > { > if (small_const_nbits(nbits)) > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 9c51ec3f0f44..613fec95ea4c 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -5205,8 +5205,10 @@ perf_output_sample_regs(struct perf_output_handle > *handle, > struct pt_regs *regs, u64 mask) > { > int bit; > + DECLARE_BITMAP(_mask, 64); > > - for_each_set_bit(bit, (const unsigned long *) &mask, > + bitmap_from_u64(_mask, mask); > + for_each_set_bit(bit, _mask, > sizeof(mask) * BITS_PER_BYTE) { > u64 val; > > diff --git a/lib/bitmap.c b/lib/bitmap.c > index c66da508cbf7..522f1b4c6078 100644 > --- a/lib/bitmap.c > +++ b/lib/bitmap.c > @@ -1170,3 +1170,22 @@ void bitmap_copy_le(unsigned long *dst, const unsigned > long *src, unsigned int n > } > EXPORT_SYMBOL(bitmap_copy_le); > #endif > + > +/* > + * bitmap_from_u64 - Check and swap words within u64. > + * @mask: source bitmap > + * @dst: destination bitmap > + * > + * In 32bit Big Endian kernel, when using (u32 *)(&val)[*] > + * to read u64 mask, we will get wrong word. > + * That is "(u32 *)(&val)[0]" gets upper 32 bits, > + * but expected could be lower 32bits of u64. > + */ > +void bitmap_from_u64(unsigned long *dst, u64 mask) > +{ > + dst[0] = mask & ULONG_MAX; > + > + if (sizeof(mask) > sizeof(unsigned long)) > + dst[1] = mask >> 32; > +} > +EXPORT_SYMBOL(bitmap_from_u64); > -- > 1.9.1 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev