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Date:   Mon, 21 Nov 2022 15:16:54 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     KP Singh <kpsingh@kernel.org>
Cc:     Chris Mason <clm@meta.com>, Steven Rostedt <rostedt@goodmis.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Florent Revest <revest@chromium.org>,
        bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Brendan Jackman <jackmanb@google.com>, markowsky@google.com,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Xu Kuohai <xukuohai@huawei.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Christoph Hellwig <hch@infradead.org>
Subject: Re: [RFC 0/1] BPF tracing for arm64 using fprobe
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On Mon, Nov 21, 2022 at 02:47:10PM +0100, KP Singh wrote:

> > > How do I know that a function return was modified by BPF? If I'm debugging
> 
> You can list the BPF programs that are loaded in the kernel with
> 
> # bpftool prog list

Only when you have access to the machine; most cases it's people sending
random splats by email.

> Also, the BPF programs show up in call stacks when you are debugging.

Only when it splats inside the BPF part, not when it splats after
because BPF changed semantics of a function.