[PATCH 6.18 171/752] hyper-v: Mark inner union in hv_kvp_exchg_msg_value as packed

Sasha Levin
2026-02-28T17:50:33Z

From: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

[ Upstream commit 1e5271393d777f6159d896943b4c44c4f3ecff52 ]

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 <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512140314.DzDxpIVn-lkp@intel.com/
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/linux-kbuild/20260110-uapi-test-disable-headers-arm-clang-unaligned-access-v1-1-b7b0fa541daa@kernel.org/
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/linux-kbuild/29b2e736-d462-45b7-a0a9-85f8d8a3de56@app.fastmail.com/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Wei Liu (Microsoft) <wei.liu@kernel.org>
Tested-by: Nicolas Schier <nsc@kernel.org>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/20260115-kbuild-alignment-vbox-v1-1-076aed1623ff@linutronix.de
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 aaa502a7bff46..1749b35ab2c21 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 {
--
2.51.0