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SubjectRe: [PATCH v6 2/2] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6_magic tests
On Wed, Feb 07, 2024 at 04:22:51PM -0800, Charlie Jenkins wrote:
> + struct csum_ipv6_magic_data {
> + const struct in6_addr saddr;
> + const struct in6_addr daddr;
> + unsigned int len;
> + __wsum csum;
> + unsigned char proto;
> + } data, *data_ptr;

Huh?

> + int num_tests = MAX_LEN / WORD_ALIGNMENT - sizeof(struct csum_ipv6_magic_data);
> +
> + for (int i = 0; i < num_tests; i++) {
> + data_ptr = (struct csum_ipv6_magic_data *)(random_buf + (i * WORD_ALIGNMENT));
> +
> + cpu_to_be32_array((__be32 *)&data.saddr, (const u32 *)&data_ptr->saddr,
> + sizeof_field(struct csum_ipv6_magic_data, saddr) / 4);
> + cpu_to_be32_array((__be32 *)&data.daddr, (const u32 *)&data_ptr->daddr,
> + sizeof_field(struct csum_ipv6_magic_data, daddr) / 4);
> + data.len = data_ptr->len;
> + data.csum = (__force __wsum)htonl((__force u32)data_ptr->csum);

What are those cpu_to_be32() about? Checksum calculations *DO* *NOT* involve
any endianness conversions. At any point.

Replace those assignments with memcpy() and be done with that - that will take
care of unaligned accesses.

Result will have host-independent memory representation. The only place where you
might want to play with byteswaps (only 16-bit ones) is if you initialized the
array of expected results with u16 constants. That will have opposite memory
representations on l-e and b-e, so you'll need to byteswap to compare with
what you get from function. Alternatively, make it an array of bytes and
do
sum16 = csum_ipv6_magic(saddr, daddr, len, proto, csum);
if (memcmp(sum16, expected_csum_ipv6_magic + i * 2, 2))
complain

That's it.

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