Re: [PATCH 3/5] lib/bitmap: add test for bitmap_{from,to}_arr64

[Guenter Roeck]

On 2/27/23 06:46, Alexander Lobakin wrote:
> From: Yury Norov <yury.norov@xxxxxxxxx>
> Date: Sat, 25 Feb 2023 16:06:45 -0800
>
> > On Sat, Feb 25, 2023 at 04:05:02PM -0800, Yury Norov wrote:
> > > On Sat, Feb 25, 2023 at 10:47:02AM -0800, Guenter Roeck wrote:
> > > > Hi,
> > > >
> > > > On Thu, Apr 28, 2022 at 01:51:14PM -0700, Yury Norov wrote:
> > > > > Test newly added bitmap_{from,to}_arr64() functions similarly to
> > > > > already existing bitmap_{from,to}_arr32() tests.
> > > > >
> > > > > Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
> > > >
> > > > Ever since this test is in the tree, several of my boot tests show
> > > > lots of messages such as
> > > >
> > > > test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001)
>
> Hmmm, the whole 4 bytes weren't touched.
>
> > > > test_bitmap: bitmap_to_arr64(nbits == 2): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000003)
> > > > test_bitmap: bitmap_to_arr64(nbits == 3): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000007)
>
> This is where it gets worse...
>
> > > > ...
> > > > test_bitmap: bitmap_to_arr64(nbits == 927): tail is not safely cleared: 0xa5a5a5a500000000 (must be 0x000000007fffffff)
> > > > test_bitmap: bitmap_to_arr64(nbits == 928): tail is not safely cleared: 0xa5a5a5a580000000 (must be 0x00000000ffffffff)
>
> I don't see the pattern how the actual result gets generated. But the
> problem is in the bitmap code rather than in the subtest -- "must be"s
> are fully correct.
>
> Given that the 0xa5s are present in the upper 32 bits, it is Big Endian
> I guess? Maybe even 32-bit Big Endian? Otherwise I'd start concerning
> how comes it doesn't reproduce on x86_64s :D

It does reproduce on 32-bit x86 builds, and as far as I can see
it is only seen with 32-bit little endian systems.

Guenter

> > > This may be a real problem. Can you share what's the system is? What's
> > > endianness and register length?
> > >
> > > + Alexander Lobakin, the author of the exact subtest.
> >
> > Forgot to add
>
> Oh, thanks for letting me know!
>
> >    
> > > > but then:
> > > >
> > > > test_bitmap: all 6550 tests passed
> > >
> > > It's because corresponding error path doesn't increment failed_tests
> > > counter. I'll send a fix shortly.
>
> [...]
>
> Thanks,
> Olek