linux-kernel - Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add support to record and check the accessed args

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Message-ID: <20240401115928.3d012be2@gandalf.local.home>
Date: Mon, 1 Apr 2024 11:59:28 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: 梦龙董 <dongmenglong.8@...edance.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Jiri Olsa
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 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau
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Subject: Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add
 support to record and check the accessed args

On Mon, 1 Apr 2024 10:28:17 +0800
梦龙董 <dongmenglong.8@...edance.com> wrote:

> On Sun, Mar 31, 2024 at 3:34 AM Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > On Sat, 30 Mar 2024 11:18:29 +0800
> > 梦龙董 <dongmenglong.8@...edance.com> wrote:
> >  
> > > > If you really want to have thousands of functions, why not just register it
> > > > with ftrace itself. It will give you the arguments via the ftrace_regs
> > > > structure. Can't you just register a program as the callback?
> > > >  
> > >
> > > Ennn...I don't understand. The main purpose for
> > > me to use TRACING is:
> > >
> > > 1. we can directly access the memory, which is more
> > >    efficient.  
> >
> > I'm not sure what you mean by the above. Access what memory?
> >  
> 
> We need to use the helper of bpf_probe_read_kernel
> when we read "skb->sk" in kprobe, and the "skb" is the
> 1st arg in ip_rcv(). And we can directly read "skb->sk"
> in tracing, which is more efficient. Isn't it?

If you add a ftrace_ops function handler that calls a BPF program, I don't
see why you can't just give it the parameters it needs instead of using bpf
helpers. It's no different than using a trampoline to do the same thing.

-- Steve