linux-kernel - Re: ftrace_direct (used by bpf trampoline) conflicts with live patch

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Date:   Thu, 31 Mar 2022 21:52:33 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Song Liu <songliubraving@...com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
        Kernel Team <Kernel-team@...com>
Subject: Re: ftrace_direct (used by bpf trampoline) conflicts with live
 patch

On Thu, 31 Mar 2022 21:48:36 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> > Does this make sense to you? Did I miss something?  
> 
> I thought the BPF trampoline does:
> 
> 	call bpf_trace_before_function
> 	call original_function + X86_PATCH_SIZE
> 	call bpf_trace_after_function
> 
> Thus, the bpf direct trampoline calls the unpatched version of the
> function call making the live patch useless. Or is this not what it
> does?

Or perhaps you are only talking about the part of bpf that does not
trace the end of a function?

-- Steve