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SubjectRe: [PATCH v8 2/2] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6_magic tests
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On 2/14/24 13:41, Charlie Jenkins wrote:
> The test cases for ip_fast_csum and csum_ipv6_magic were failing on a
> variety of architectures that are big endian or do not support
> misalgined accesses. Both of these test cases are changed to support big
> and little endian architectures.
>
> The test for ip_fast_csum is changed to align the data along (14 +
> NET_IP_ALIGN) bytes which is the alignment of an IP header. The test for
> csum_ipv6_magic aligns the data using a struct. An extra padding field
> is added to the struct to ensure that the size of the struct is the same
> on all architectures (44 bytes).
>
> The test for csum_ipv6_magic somewhat arbitrarily aligned saddr and
> daddr. This would fail on parisc64 due to the following code snippet in
> arch/parisc/include/asm/checksum.h:
>
> add %4, %0, %0\n"
> ldd,ma 8(%1), %6\n"
> ldd,ma 8(%2), %7\n"
> add,dc %5, %0, %0\n"
>
> The second add is expecting carry flags from the first add. Normally,
> a double word load (ldd) does not modify the carry flags. However,
> because saddr and daddr may be misaligned, ldd triggers a misalignment
> trap that gets handled in arch/parisc/kernel/unaligned.c. This causes
> many additional instructions to be executed between the two adds. This
> can be easily solved by adding the carry into %0 before executing the
> ldd.
>
> However, that is not necessary since ipv6 headers should always be
> aligned on a 16-byte boundary on parisc since NET_IP_ALIGN is set to 2
> and the ethernet header size is 14.
>
> Architectures that set NET_IP_ALIGN to 0 must support misaligned saddr
> and daddr, but that is not tested here.
>
> Fixes: 6f4c45cbcb00 ("kunit: Add tests for csum_ipv6_magic and ip_fast_csum")
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>

Reviewed-and-Tested-by: Guenter Roeck <linux@roeck-us.net>

Guenter



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