Re: [PATCH] selftests: net: tcp_ao: don't shift a size_t by 32

[David Laight <david.laight.linux@gmail.com>]

On Tue,  3 Nov 2026 11:39:21 -0500
Sasha Levin <sashal@kernel.org> wrote:

> gen_tcp_addr() shifts the size_t n right by 32 and masks it with BIT(32)
> - 1. On 32-bit architectures both shifts are as wide as the type, which
> is undefined:
> 
>   aolib.h:230:40: warning: right shift count >= width of type [-Wshift-count-overflow]
> 
> Convert n to uint64_t first and mask with 0xffffffff.
> 
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> Found with 32-bit builds of the selftests (gcc 16 and clang 21 with
> -m32, with and without -D_TIME_BITS=64 -D_FILE_OFFSET_BITS=64);
> KernelCI's 32-bit arm builds show the same warnings. The changed files
> build without them now, and the x86_64 builds don't change.
> 
>  tools/testing/selftests/net/tcp_ao/lib/aolib.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/net/tcp_ao/lib/aolib.h b/tools/testing/selftests/net/tcp_ao/lib/aolib.h
> index 53be1744237ee..71ff975533089 100644
> --- a/tools/testing/selftests/net/tcp_ao/lib/aolib.h
> +++ b/tools/testing/selftests/net/tcp_ao/lib/aolib.h
> @@ -226,8 +226,8 @@ static inline union tcp_addr gen_tcp_addr(union tcp_addr net, size_t n)
>  	union tcp_addr ret = net;
>  
>  #ifdef IPV6_TEST
> -	ret.a6.s6_addr32[3] = htonl(n & (BIT(32) - 1));
> -	ret.a6.s6_addr32[2] = htonl((n >> 32) & (BIT(32) - 1));
> +	ret.a6.s6_addr32[3] = htonl((uint64_t)n & 0xffffffff);

You don't need a cast or mask there.

> +	ret.a6.s6_addr32[2] = htonl((uint64_t)n >> 32);

That can also be n >> 16 >> 16

Also see upper_32_bits() and lower_32_bits() in wordpart.h
which might not be available for selftests?

David


>  #else
>  	ret.a4.s_addr = htonl(ntohl(net.a4.s_addr) + n);
>  #endif