On Tue, Feb 08, 2022 at 06:16:35AM +0100, Ilya Leoshkevich wrote:
> orig_x0's location is used by libbpf tracing macros, therefore it
> should not be moved.
>
> Suggested-by: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> ---
> arch/arm64/include/asm/ptrace.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index 41b332c054ab..7e34c3737839 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -185,6 +185,10 @@ struct pt_regs {
> u64 pstate;
> };
> };
> + /*
> + * orig_x0 is not exposed via struct user_pt_regs, but its location is
> + * assumed by libbpf's tracing macros, so it should not be moved.
> + */
In other words this comment is saying that the layout is ABI.
That's not the case. orig_x0 here and equivalent on s390 can be moved.
It will break bpf progs written without CO-RE and that is expected.
Non CO-RE programs often do all kinds of bpf_probe_read_kernel and
will be breaking when kernel layout is changing.
I suggest to drop this patch and patch 12.
