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Date:   Tue, 27 Oct 2020 09:14:01 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Jiri Olsa <jolsa@redhat.com>, Jiri Olsa <jolsa@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andriin@fb.com>, netdev@vger.kernel.org,
        bpf@vger.kernel.org, Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
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        <toke@redhat.com>, Viktor Malik <vmalik@redhat.com>
Subject: Re: [RFC bpf-next 00/16] bpf: Speed up trampoline attach
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On Mon, 26 Oct 2020 21:30:14 -0700
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> > Direct calls wasn't added so that bpf and ftrace could co-exist, it was
> > that for certain cases, bpf wanted a faster way to access arguments,
> > because it still worked with ftrace, but the saving of regs was too
> > strenuous.  
> 
> Direct calls in ftrace were done so that ftrace and trampoline can co-exist.
> There is no other use for it.

What does that even mean? And I'm guessing when you say "trampoline"
you mean a "bpf trampoline" because "trampoline" is used for a lot more
than bpf, and bpf does not own that term.

Do you mean, "direct calls in ftrace were done so that bpf trampolines
could work". Remember, ftrace has a lot of users, and it must remain
backward compatible.

-- Steve