linux-kernel - Re: [RFC PATCH v6 0/2] Make eBPF programs output data to perf

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Message-ID: <55CD10EE.7000300@plumgrid.com>
Date:	Thu, 13 Aug 2015 14:49:34 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	pi3orama <pi3orama@....com>
Cc:	He Kuang <hekuang@...wei.com>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"masami.hiramatsu.pt@...achi.com" <masami.hiramatsu.pt@...achi.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"wangnan0@...wei.com" <wangnan0@...wei.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v6 0/2] Make eBPF programs output data to perf

On 8/13/15 2:35 PM, pi3orama wrote:
> I was thinking about whether to add a "type" field there, so we will have an explicit
> mov const instruction before the call instruction, which can act as a mark. Also, if
> we generate the type code automatically, a type field in this API can make things
> easier since we don't need wrap the user structure in BPF stack. However, the
> LLVM side is not ready yet, so we haven't post the new version.

I think the helper was clean enough. Any type info probably needs to be
done as a side channel and not part of the helper anyway.
But, ok, let's figure out the type stuff first.
Also I don't think you can rely on extra insn in front of a call insn.
Compiler can freely insert other insns there. You don't want to
introduce data flow analysis in elf parser.

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