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    SubjectRe: [PATCH tracing/kprobes v2 1/5] tracing/kprobes: Rename special variables syntax
    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?



    > > %return = return value
    >
    > or %retval? :)


    Yeah, better!


    >
    >> @return = return addr
    >
    > I'd like to remove it, because it's already shown.


    Ok.



    >> 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?



    >> [Perf probe only]
    >>
    >> var = variable name, global or local, we can deal with shadow issues later
    >> through variable scope: func_name:var, filename:var, whatever for now
    >> it's not a problem. Local also includes argument names.
    >
    > That's fine to me. :-)
    >


    Great :)
    Thanks!



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