linux-kernel - Re: [PATCH 2/3] tracing/kprobes: Make Kconfig dependencies generic

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Date:	Thu, 18 Feb 2010 11:19:54 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Mike Frysinger <vapier.adi@...il.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"David S . Miller" <davem@...emloft.net>,
	Paul Mundt <lethal@...ux-sh.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/3] tracing/kprobes: Make Kconfig dependencies generic

Frederic Weisbecker wrote:
> On Thu, Feb 18, 2010 at 09:01:12AM -0500, Mike Frysinger wrote:
>>> --- a/arch/Kconfig
>>> +++ b/arch/Kconfig
>>> @@ -123,6 +123,10 @@ config USE_GENERIC_SMP_HELPERS
>>>
>>>  config HAVE_REGS_AND_STACK_ACCESS_API
>>>        bool
>>> +       help
>>> +         This symbol should be selected by an architecure if it supports
>>> +         the API needed to access registers and stack entries from pt_regs.
>>> +         For example the kprobes-based event tracer needs this API.
>>
>> a bit vague ... arent there headers/functions people could look at ?
>> perhaps you're talking about the regset functions (which is an API to
>> access registers in pt_regs) ?  or you're talking about asm/syscall.h
>> (which is an API to access registers in pt_regs) ?
>>
>> i'm not asking to be a pain, i'm asking because i really havent a
>> clue.  if i wanted to add support for this stuff to the Blackfin arch,
>> i wouldnt know where to start.  even after reading this help i'd fall
>> back to grepping arch/x86/ and trying to divine a starting point from
>> there.
> 
> 
> If an arch support kprobes, it just needs to select
> HAVE_REGS_AND_STACK_ACCESS_API to figure out quickly what is missing,
> as gcc will barf every missing clues you need.

These APIs are needed for kprobe-tracer on ftrace(kernel/trace/trace_kprobe.c), 
which is just a consumer of kprobes (so depends on CONFIG_KPROBES).

I mean, if you wanna figure out that, you have to select CONFIG_KPROBE_EVENT too :)
And then, gcc tries to compile trace_kprobe.c and quickly dumps error messages
what APIs are not found :)

> For now it is stored is asm/ptrace.h, but that might be split in
> the future, especially as ptrace has initially nothing related to
> that. A documentation that deals with filenames or API enumerations
> tend to be incidentally async with API evolutions.

yeah, now those APIs depend on pt_regs, so I put it in ptrace.h.

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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