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

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Message-ID: <20210415142120.7427b4bd@gandalf.local.home>
Date:   Thu, 15 Apr 2021 14:21:20 -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 Thu, 15 Apr 2021 14:18:31 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> My last release of that code is here:
> 
>   https://lore.kernel.org/lkml/20190525031633.811342628@goodmis.org/
> 
> It allows you to "reserve data" to pass from the caller to the return, and
> that could hold the arguments. See patch 15 of that series.

Note that implementation only lets you save up to 4 words on the stack, but
that can be changed. Or you could have a separate shadow stack for saving
arguments, and only pass the pointer to the location on the other stack
where those arguments are.

-- Steve