csum_partial() on different archs (selftest/bpf)

[Eric Dumazet]

On 11/13/20 11:36 AM, Björn Töpel wrote:
> I was running the selftest/bpf on riscv, and had a closer look at one
> of the failing cases:
> 
>   #14/p valid read map access into a read-only array 2 FAIL retval
> 65507 != -29 (run 1/1)
> 
> The test does a csum_partial() call via a BPF helper. riscv uses the
> generic implementation. arm64 uses the generic csum_partial() and fail
> in the same way [1]. arm (32-bit) has a arch specfic implementation,
> and fail in another way (FAIL retval 131042 != -29) [2].
> 
> I mimicked the test case in a userland program, comparing the generic
> csum_partial() to the x86 implementation [3], and the generic and x86
> implementation does yield a different result.
> 
> x86     :    -29 : 0xffffffe3
> generic :  65507 : 0x0000ffe3
> arm     : 131042 : 0x0001ffe2
> 
> Who is correct? :-) It would be nice to get rid of this failed case...
> 

There are all the same value :), they all fold to u16  0xFFE3

Maybe the test needs a fix, there is a missing folding.

> 
> Thanks,
> Björn
> 
> 
> [1] https://qa-reports.linaro.org/lkft/linux-next-master/build/next-20201112/testrun/3430401/suite/kselftest/test/bpf.test_verifier/log
> [2] https://qa-reports.linaro.org/lkft/linux-mainline-master/build/v5.10-rc3-207-g585e5b17b92d/testrun/3432361/suite/kselftest/test/bpf.test_verifier/log
> [3] https://gist.github.com/bjoto/dc22d593aa3ac63c2c90632de5ed82e0
>