Messages in this thread | | | Date | Thu, 11 Aug 2016 14:27:10 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] perf/core: Fix the mask in perf_output_sample_regs |
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Sorry, found it in my inbox while clearing out backlog..
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.
But it looks an awful lot like it..
> +++ 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;
> +++ b/lib/bitmap.c
> +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);
Looks small enough for an inline.
Alternatively you can go all the way and add bitmap_from_u64array(), but that seems massive overkill.
Tedious stuff.. I can't come up with anything prettier :/
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