[PATCH bpf-next v3 2/4] libbpf: Access first syscall argument with CO-RE direct read on arm64

[Xu Kuohai]

On 8/31/2024 12:19 PM, Pu Lehui wrote:
> From: Pu Lehui <pulehui at huawei.com>
> 
> Currently PT_REGS_PARM1 SYSCALL(x) is consistent with PT_REGS_PARM1_CORE
> SYSCALL(x), which will introduce the overhead of BPF_CORE_READ(), taking
> into account the read pt_regs comes directly from the context, let's use
> CO-RE direct read to access the first system call argument.
> 
> Suggested-by: Andrii Nakryiko <andrii at kernel.org>
> Signed-off-by: Pu Lehui <pulehui at huawei.com>
> ---
>   tools/lib/bpf/bpf_tracing.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
> index e7d9382efeb3..051c408e6aed 100644
> --- a/tools/lib/bpf/bpf_tracing.h
> +++ b/tools/lib/bpf/bpf_tracing.h
> @@ -222,7 +222,7 @@ struct pt_regs___s390 {
>   
>   struct pt_regs___arm64 {
>   	unsigned long orig_x0;
> -};
> +} __attribute__((preserve_access_index));
>   
>   /* arm64 provides struct user_pt_regs instead of struct pt_regs to userspace */
>   #define __PT_REGS_CAST(x) ((const struct user_pt_regs *)(x))
> @@ -241,7 +241,7 @@ struct pt_regs___arm64 {
>   #define __PT_PARM4_SYSCALL_REG __PT_PARM4_REG
>   #define __PT_PARM5_SYSCALL_REG __PT_PARM5_REG
>   #define __PT_PARM6_SYSCALL_REG __PT_PARM6_REG
> -#define PT_REGS_PARM1_SYSCALL(x) PT_REGS_PARM1_CORE_SYSCALL(x)
> +#define PT_REGS_PARM1_SYSCALL(x) (((const struct pt_regs___arm64 *)(x))->orig_x0)
>   #define PT_REGS_PARM1_CORE_SYSCALL(x) \
>   	BPF_CORE_READ((const struct pt_regs___arm64 *)(x), __PT_PARM1_SYSCALL_REG)
>   

Cool!

Acked-by: Xu Kuohai <xukuohai at huawei.com>