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

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Message-ID: <2379c139-6457-49dc-84fa-0d60ce226f2a@huaweicloud.com>
Date: Sat, 31 Aug 2024 15:26:46 +0800
From: Xu Kuohai <xukuohai@...weicloud.com>
To: Pu Lehui <pulehui@...weicloud.com>, bpf@...r.kernel.org,
 linux-riscv@...ts.infradead.org, netdev@...r.kernel.org,
 Andrii Nakryiko <andrii@...nel.org>
Cc: Björn Töpel <bjorn@...nel.org>,
 Ilya Leoshkevich <iii@...ux.ibm.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Puranjay Mohan <puranjay@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>, Pu Lehui <pulehui@...wei.com>
Subject: Re: [PATCH bpf-next v3 2/4] libbpf: Access first syscall argument
 with CO-RE direct read on arm64

On 8/31/2024 12:19 PM, Pu Lehui wrote:
> From: Pu Lehui <pulehui@...wei.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@...nel.org>
> Signed-off-by: Pu Lehui <pulehui@...wei.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@...wei.com>