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

[Alexander Lobakin]

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

>>
>> 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