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. > > 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 thanks, jirka _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
