linux-kernel - Re: [RFC bpf-next 4/4] selftests/bpf: Add attach bench test

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Message-ID: <20220418133330.6241014c@gandalf.local.home>
Date:   Mon, 18 Apr 2022 13:33:30 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [RFC bpf-next 4/4] selftests/bpf: Add attach bench test

On Sat, 16 Apr 2022 23:21:03 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> But it seems that __bpf_tramp_exit() doesn't call __fentry__. (I objdump'ed) 
> 
> ffffffff81208270 <__bpf_tramp_exit>:
> ffffffff81208270:       55                      push   %rbp
> ffffffff81208271:       48 89 e5                mov    %rsp,%rbp
> ffffffff81208274:       53                      push   %rbx
> ffffffff81208275:       48 89 fb                mov    %rdi,%rbx
> ffffffff81208278:       e8 83 70 ef ff          callq  ffffffff810ff300 <__rcu_read_lock>
> ffffffff8120827d:       31 d2                   xor    %edx,%edx
> 
> 
> > 
> > So it's quite bizarre and inconsistent.  
> 
> Indeed. I guess there is a bug in scripts/recordmcount.pl.

Actually, x86 doesn't use that script. It either uses the C version, or
with latest gcc, it is created by the compiler itself.

I'll look deeper into it.

-- Steve