On Tue, Jun 25, 2019 at 4:07 AM Baruch Siach <baruch@xxxxxxxxxx> wrote:
>
> Merge commit 1c8c5a9d38f60 ("Merge
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next") undid the
> fix from commit 36f9814a494 ("bpf: fix uapi hole for 32 bit compat
> applications") by taking the gpl_compatible 1-bit field definition from
> commit b85fab0e67b162 ("bpf: Add gpl_compatible flag to struct
> bpf_prog_info") as is. That breaks architectures with 16-bit alignment
> like m68k. Embed gpl_compatible into an anonymous union with 32-bit pad
> member to restore alignment of following fields.
>
> Thanks to Dmitry V. Levin his analysis of this bug history.
>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Baruch Siach <baruch@xxxxxxxxxx>
> ---
> v2:
> Use anonymous union with pad to make it less likely to break again in
> the future.
> ---
> include/uapi/linux/bpf.h | 5 ++++-
> tools/include/uapi/linux/bpf.h | 5 ++++-
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a8b823c30b43..766eae02d7ae 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3142,7 +3142,10 @@ struct bpf_prog_info {
> __aligned_u64 map_ids;
> char name[BPF_OBJ_NAME_LEN];
> __u32 ifindex;
> - __u32 gpl_compatible:1;
> + union {
> + __u32 gpl_compatible:1;
> + __u32 pad;
> + };
Nack for the reasons explained in the previous thread
on the same subject.
Why cannot you go with earlier suggestion of _u32 :31; ?
