linux-kernel - Re: [RFC PATCH v2 09/15] perf probe: Support $params without debuginfo

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Date:	Fri, 29 May 2015 14:30:42 +0800
From:	He Kuang <hekuang@...wei.com>
To:	Alexei Starovoitov <ast@...mgrid.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	<wangnan0@...wei.com>, <paulus@...ba.org>,
	<a.p.zijlstra@...llo.nl>, <mingo@...hat.com>, <acme@...nel.org>,
	<namhyung@...nel.org>, <jolsa@...nel.org>, <dsahern@...il.com>,
	<brendan.d.gregg@...il.com>, <daniel@...earbox.net>
CC:	<lizefan@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 09/15] perf probe: Support $params without
 debuginfo

hi, Alexei

On 2015/5/29 2:10, Alexei Starovoitov wrote:
> On 5/28/15 6:01 AM, He Kuang wrote:
>>> I don't think you can break it down in two steps like this.
>>>> There is no such thing as 'calling regs'. x86_32 with ax,dx,cx
>>>> are not 'calling regs'. 64-bit values will be passed in a pair.
>>>> Only 'pt_regs + arch + func_proto + asmlinkage' makes sense
>>> >from the user point of view.
>>>> Adding 'asmlinkage' attr is also trivial.
>>>> 'func(long, char) asmlinkage' is easy to parse and the user
>> I think at this early stage, we could make our bpf variable
>> prologue work with debuginfo while keeping bpf 'SEC' syntax
>> consistent with original perf probe. After all, we can use
>> pt_regs directly or relay to perf-probe cache by Masami to deal
>> with non-debug cases.
> 
> so you're saying you don't want to support non-debug case for now?
> Sure, as long as section name parser will be able to support
> 'func(long, char) asmlinkage' syntax in the future without breaking
> compatibility. I'm mostly interested in cases when debug info
> is not available at all. So perf-probe cache is of no use to me.
> 
> 

Yes, that syntax do deal with the situation which current 'perf
probe' syntax not covered, so not only bpf prologue would benifit
from that, maybe we could try to let perf probe involve that.

Thanks.

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