[v2] alloc_tag: avoid implicit padding in uapi

[PATCH] [v2] alloc_tag: avoid implicit padding in uapi

Posted by Arnd Bergmann 1 week, 1 day ago

From: Arnd Bergmann <arnd@arndb.de>

The implied padding causes a harmless warning when testing the uapi
headers with -Wpadded that could in theory indicate incompatibilities
or data leaks:

./usr/include/linux/alloc_tag.h:41:1: error: padding struct size to alignment boundary with 7 bytes [-Werror=padded]

The code here is fine, but it's better to make the padding explicit
and avoid the warning here.

Acked-by: SJ Park <sj@kernel.org>
Acked-by: Hao Ge <hao.ge@linux.dev>
Fixes: 1d581ab2348c ("alloc_tag: add ioctl to /proc/allocinfo")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2; fix changelog typos
---
 include/uapi/linux/alloc_tag.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h
index e3ad94444864..7d4618bea043 100644
--- a/include/uapi/linux/alloc_tag.h
+++ b/include/uapi/linux/alloc_tag.h
@@ -38,6 +38,7 @@ struct allocinfo_counter {
 	__u64 bytes;
 	__u64 calls;
 	__u8 accurate;
+	__u8 pad[7];
 } __attribute__((aligned(8)));
 
 struct allocinfo_tag_data {
-- 
2.53.0

Re: [PATCH] [v2] alloc_tag: avoid implicit padding in uapi

Posted by Suren Baghdasaryan 1 week, 1 day ago

On Tue, Sep 15, 2026 at 11:58 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> The implied padding causes a harmless warning when testing the uapi
> headers with -Wpadded that could in theory indicate incompatibilities
> or data leaks:
>
> ./usr/include/linux/alloc_tag.h:41:1: error: padding struct size to alignment boundary with 7 bytes [-Werror=padded]
>
> The code here is fine, but it's better to make the padding explicit
> and avoid the warning here.
>
> Acked-by: SJ Park <sj@kernel.org>
> Acked-by: Hao Ge <hao.ge@linux.dev>
> Fixes: 1d581ab2348c ("alloc_tag: add ioctl to /proc/allocinfo")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Suren Baghdasaryan <surenb@google.com>

> ---
> v2; fix changelog typos
> ---
>  include/uapi/linux/alloc_tag.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h
> index e3ad94444864..7d4618bea043 100644
> --- a/include/uapi/linux/alloc_tag.h
> +++ b/include/uapi/linux/alloc_tag.h
> @@ -38,6 +38,7 @@ struct allocinfo_counter {
>         __u64 bytes;
>         __u64 calls;
>         __u8 accurate;
> +       __u8 pad[7];
>  } __attribute__((aligned(8)));
>
>  struct allocinfo_tag_data {
> --
> 2.53.0
>