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Message-ID: <4ACA25D5.10703@redhat.com>
Date: Mon, 05 Oct 2009 12:59:01 -0400
From: Masami Hiramatsu <mhiramat@...hat.com>
To: Frederic Weisbecker <fweisbec@...il.com>
CC: Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
lkml <linux-kernel@...r.kernel.org>,
systemtap <systemtap@...rces.redhat.com>,
DLE <dle-develop@...ts.sourceforge.net>,
Thomas Gleixner <tglx@...utronix.de>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Mike Galbraith <efault@....de>,
Paul Mackerras <paulus@...ba.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Christoph Hellwig <hch@...radead.org>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Jim Keniston <jkenisto@...ibm.com>,
"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [PATCH tracing/kprobes v2 1/5] tracing/kprobes: Rename special
variables syntax
Masami Hiramatsu wrote:
> Frederic Weisbecker wrote:
>> On Fri, Oct 02, 2009 at 05:48:42PM -0400, Masami Hiramatsu wrote:
>>> FETCHARGS : Arguments. Each probe can have up to 128 args.
>>> %REG : Fetch register REG
>>> - sN : Fetch Nth entry of stack (N>= 0)
>>> - sa : Fetch stack address.
>>> @ADDR : Fetch memory at ADDR (ADDR should be in kernel)
>>> @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
>>> - aN : Fetch function argument. (N>= 0)(*)
>>> - rv : Fetch return value.(**)
>>> - ra : Fetch return address.(**)
>>> + $sN : Fetch Nth entry of stack (N>= 0)
>>> + $sa : Fetch stack address.
>>> + $aN : Fetch function argument. (N>= 0)(*)
>>> + $rv : Fetch return value.(**)
>>> + $ra : Fetch return address.(**)
>>
>>
>>
>> I feel uncomfortable with that, because of bash scripts that
>> may use it and always need to escape it with antislashes or
>> use single quotes for it to not be replaced by a random variable
>> value. If one uses double quotes without antislashes to protect
>> the command line, the result is unpredictable, depending of
>> the current set of variables...
>>
>> May be we can use # instead of $ ? That's a kind of pity because
>> $ suggested a variable whereas # suggests a constant, we are then
>> losing this self-explainable characteristic for kprobes
>> "specific variable fetchs". But that will work without ambiguity.
>
> Hmm, # is widely used for comment, including some kernel pseudo
> file interfaces, kprobe_events too. Comments are useful if a
> probe list is restored from a file.
>
> For accessing local variables, kprobe-tracer needs to support *at least*
> below variables:
> - Registers
> - Stack address (if a register points stack address, this isn't needed)
>
> Below special vars are complementary aliases.
> - Function arguments
> - Return value
> - Return address
>
> and I'd like perf-probe to have a transparent syntax with kprobe-tracer.
>
> This means, if we can remove special vars except registers, or rename it
> non-conflictable name with registers, we just need to separate name spaces
> of
> - Regsiters
> - Local variables
>
> Here, local variables will support fields of data structs, and it will
> use '->' expression. Since'>' means redirection in bash, local variables
> need to be *escaped* in this case. Thus, I think we can use '$' prefix
> for it. (I'm OK, because this is similar syntax to systemtap:-).
>
> So, if you don't like %regs, $svars and locals, we can use regs and $locals :-)
As far as I can see in arch/*/include/asm/ptrace.h, all registers start with
alphabets :-). So, I'd like to suggest renaming sp-vars to '_sp-vars'.
Then, we will have;
- $local-vars
- @global-symbol
- regs
- _sp-vars
- +|-Offs(ARG)
Thank you,
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division
e-mail: mhiramat@...hat.com
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