On Thu, Jan 15, 2026 at 08:35:44AM +0100, Thomas Weißschuh wrote:
> The unpacked union within a packed struct generates alignment warnings
> on clang for 32-bit ARM:
>
> ./usr/include/linux/hyperv.h:361:2: error: field within 'struct
> hv_kvp_exchg_msg_value'
> is less aligned than 'union hv_kvp_exchg_msg_value::(anonymous at
> ./usr/include/linux/hyperv.h:361:2)'
> and is usually due to 'struct hv_kvp_exchg_msg_value' being packed,
> which can lead to unaligned accesses [-Werror,-Wunaligned-access]
> 361 | union {
> | ^
>
> With the recent changes to compile-test the UAPI headers in more cases,
> this warning in combination with CONFIG_WERROR breaks the build.
>
> Fix the warning.
>
> Reported-by: kernel test robot <[email protected]>
> Closes:
> https://lore.kernel.org/oe-kbuild-all/[email protected]/
> Reported-by: Nathan Chancellor <[email protected]>
> Closes:
> https://lore.kernel.org/linux-kbuild/20260110-uapi-test-disable-headers-arm-clang-unaligned-access-v1-1-b7b0fa541...@kernel.org/
> Suggested-by: Arnd Bergmann <[email protected]>
> Link:
> https://lore.kernel.org/linux-kbuild/[email protected]/
> Signed-off-by: Thomas Weißschuh <[email protected]>
Acked-by: Wei Liu (Microsoft) <[email protected]>
> ---
> include/uapi/linux/hyperv.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/hyperv.h b/include/uapi/linux/hyperv.h
> index aaa502a7bff4..1749b35ab2c2 100644
> --- a/include/uapi/linux/hyperv.h
> +++ b/include/uapi/linux/hyperv.h
> @@ -362,7 +362,7 @@ struct hv_kvp_exchg_msg_value {
> __u8 value[HV_KVP_EXCHANGE_MAX_VALUE_SIZE];
> __u32 value_u32;
> __u64 value_u64;
> - };
> + } __attribute__((packed));
> } __attribute__((packed));
>
> struct hv_kvp_msg_enumerate {
>
> --
> 2.52.0
>
>
