Re: [PATCH tracing/kprobes v2 1/5] tracing/kprobes: Rename specialvariables syntax

[Masami Hiramatsu]

Frederic Weisbecker wrote:
> On Mon, Oct 05, 2009 at 04:18:39PM -0400, Masami Hiramatsu wrote:
> > Frederic Weisbecker wrote:
> > > For the function arguments, I guess we don't need to worry
> > > anymore about r0, r1, etc... but we can deal with the true var
> > > name, without any kind of prefixes.
> >
> > This depends on ABI, function argument from ABI doesn't need
> > debuginfo, but it will be unstable on some arch, e.g. x86-32
> > with/without asmlinkage.
> >
> > Thus, I think that we can just describe where function arguments
> > will be(e.g. arg0 is ax) as a note for each architecture
> > in Documents/trace/kprobetrace.txt.
>
>
> Yeah that may help. Although everyone can look at the calling convention
> ABI for a given arch but that would still help.
>
>
> > > What about @return :-) ?
> >
> > Hmm, it might conflict with global symbol... Maybe, we can remove this
> > because retprobe already shows return address in the head of entry.
>
>
> It won't conflict since "return" is a reserved word and can't then be
> used as a symbol.
>
> But yeah, if it's an embeded field, we should remove it.
>
>
> > > What if we take the following:
> > >
> > > [Ftrace and perf probe side]
> > >
> > > %reg = registers, we can also play with deref and offsets like (%esp), 8(%esp), etc.
> >
> > Hmm, on x86-32, sp at intr context is not pointing the top of stack. actually&sp is
> > the real address of the stack :(
> > Perhaps, on x86-32, we can translate %sp to stack address in kprobe-tracer.
>
>
> Oh? You mean in the saved registers while triggering an int 3?

Yes, interrupt/exception handlers don't save sp on x86-32.

> > > arg(n) = arg number, where n is the number
> >
> > How about %N? or just adds a note in documents.
>
>
> Hmm, the problem is that %1, %2, etc. is not very self-explainable.
>
> May be %arg1, %arg2, etc.. But would that sound confusing since we
> have % for registers?

As I sent right now, how about %argumentN ? it will not conflict with
register names...

Thank you,

--
Masami Hiramatsu

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

e-mail: mhiramat@xxxxxxxxxx

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