netdev - Re: [PATCHv2 RFC bpf-next 0/7] bpf: Add support for ftrace probe

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Date:   Mon, 19 Apr 2021 18:00:24 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...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>, Daniel Xu <dxu@...uu.xyz>,
        Jesper Brouer <jbrouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Viktor Malik <vmalik@...hat.com>
Subject: Re: [PATCHv2 RFC bpf-next 0/7] bpf: Add support for ftrace probe

On Mon, 19 Apr 2021 22:51:46 +0200
Jiri Olsa <jolsa@...hat.com> wrote:

> now, it looks like the fgraph_ops entry callback does not have access
> to registers.. once we have that, we could store arguments for the exit
> callback and have all in place.. could this be added? ;-)

Sure. The only problem is that we need to do this carefully to not break
all the architectures that support function graph tracing.

For function tracing, I usually add "CONFIG_HAVE_..." configs that state if
the architecture supports some ftrace feature, and if it does it can use a
different callback prototype. But it does get messy.

Ideally, I would love to go and update all architectures to support all
features, but that requires understanding the assembly of all those
architectures :-p

To test that I don't break other archs, I usually just support x86_64 and
leave x86_32 behind. I mean, who cares about x86_32 anymore ;-)

-- Steve