linux-kernel - Re: [PATCH v3 perf, bpf-next 1/4] perf, bpf: Introduce PERF_RECORD_BPF

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Date:   Thu, 13 Dec 2018 16:25:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "acme@...nel.org" <acme@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v3 perf, bpf-next 1/4] perf, bpf: Introduce
 PERF_RECORD_BPF_EVENT

On Wed, Dec 12, 2018 at 06:56:11PM +0000, Song Liu wrote:
> 
> 
> > On Dec 12, 2018, at 10:05 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > On Wed, Dec 12, 2018 at 05:09:17PM +0000, Song Liu wrote:
> >>> And while this tracks the bpf kallsyms, it does not do all kallsyms.
> >>> 
> >>> .... Oooh, I see the problem, everybody is doing their own custom
> >>> kallsym_{add,del}() thing, instead of having that in generic code :-(
> >>> 
> >>> This, for example, doesn't track module load/unload nor ftrace
> >>> trampolines, even though both affect kallsyms.
> >> 
> >> I think we can use PERF_RECORD_MMAP(or MMAP2) for module load/unload. 
> >> That could be separate sets of patches. 
> > 
> > So I would actually like to move bpf_lock/bpf_kallsyms/bpf_tree +
> > bpf_prog_kallsyms_*() + __bpf_address_lookup() into kernel/kallsyms.c
> > and also have ftrace use that.
> > 
> > Because currently the ftrace stuff is otherwise invisible.
> > 
> > A generic kallsym register/unregister for any JIT.
> 
> I guess this is _not_ a requirement for this patchset? BPF program has
> special data (id, sub_id, tag) that we need PERF_RECORD_BPF_EVENT. So 
> this patchset should be orthogonal to the generic kallsym framework?

Well, it is a question of ABI. I don't like mixing the kallsym updates
with the BPF updates.