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

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Message-ID: <5568FC5F.40504@hitachi.com>
Date:	Sat, 30 May 2015 08:55:11 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	He Kuang <hekuang@...wei.com>,
	Alexei Starovoitov <ast@...mgrid.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,
	cti.systems-productivity-manager.ts@...achi.com
Subject: Re: Re: [RFC PATCH v2 09/15] perf probe: Support $params without
 debuginfo

On 2015/05/29 15:30, He Kuang wrote:
> 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.

Hmm, then how about below syntax?

 perf probe x86_acpi_enter_sleep_state $regparams:asmlinkage(char)

So, regparams has following synopsis.

 $regparams[:[asmlinkage|0-6]([u8|u16|u32|u64|ptr][,...])]

Note that asmlinkage is a synonym of 0, and default depends on arch :)
Some architecture ignores this part, e.g. x86_64 always uses regs.
And it is automatically expanded to argX="%reg or $stackX".

e.g.
 $regparams is expanded to
  arg1=%di arg2=%si arg3=%dx arg4=%cx arg5=%r8 arg6=%r9 (on x86_64)
  arg1=%ax arg2=%dx arg3=%cx arg4=$stack1 arg5=$stack2 arg6=$stack3 (on i386)

 $regparams:0 is expanded to
  arg1=%di arg2=%si arg3=%dx arg4=%cx arg5=%r8 arg6=%r9 (on x86_64)
  arg1=$stack1 arg2=$stack2 arg3=$stack3 arg4=$stack4 arg5=$stack5 arg6=$stack6 (on i386)

 $regparams:3(char,long) is expanded to
  arg1=%di:s8 arg2=%si:s64 (on x86_64)
  arg1=%ax:s8 arg2=%dx:s64 (on i386)

How is this?

Thank you,


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@...achi.com
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