On Monday 20 June 2016 03:10 PM, Jiri Olsa wrote: > On Mon, Jun 20, 2016 at 05:27:25PM +0800, Wangnan (F) wrote: >> >> On 2016/6/20 17:18, Jiri Olsa wrote: >>> On Mon, Jun 20, 2016 at 02:14:01PM +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. >>>> "mask" is of type "u64", but sent as a "unsigned long *" to >>>> lib functions along with sizeof(). While the exisitng code works fine in >>>> most of the case, the logic is broken when using a 32bit perf on a >>>> 64bit kernel (Big Endian). We end up reading the wrong word of the u64 >>>> first in the lib functions. >>> hum, I still don't see why this happens.. why do we read the >>> wrong word in this case? >> If you read a u64 using (u32 *)(&val)[0] and (u32 *)(&val)[1] >> you can get wrong value. This is what _find_next_bit() is doing.
Also in find_first_bit(). >> >> In a big endian environment where 'unsigned long' is 32 bits >> long, "(u32 *)(&val)[0]" gets upper 32 bits, but without this patch >> perf assumes it gets lower 32 bits. The root cause is wrongly convert >> u64 value to bitmap. > i see, could you please put this into comment in the code? > > also we could have common function for that, to keep it on > one place only, like bitmap_from_u64 or so Sure will do. > > thanks, > jirka > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
