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    SubjectRe: [PATCH 2/2] ftrace: support for PowerPC

    On Wed, 14 May 2008, David Miller wrote:

    > From: Steven Rostedt <rostedt@goodmis.org>
    > Date: Wed, 14 May 2008 23:49:44 -0400
    >
    > > +#ifdef CONFIG_FTRACE
    > > +#ifdef CONFIG_DYNAMIC_FTRACE
    > > +_GLOBAL(mcount)
    > > +_GLOBAL(_mcount)
    > > + stwu r1,-48(r1)
    > > + stw r3, 12(r1)
    > > + stw r4, 16(r1)
    > > + stw r5, 20(r1)
    > > + stw r6, 24(r1)
    > > + mflr r3
    > > + stw r7, 28(r1)
    > > + mfcr r5
    > > + stw r8, 32(r1)
    > > + stw r9, 36(r1)
    > > + stw r10,40(r1)
    > > + stw r3, 44(r1)
    > > + stw r5, 8(r1)
    >
    > Yikes, that's really expensive.

    Well, at least with dynamic ftrace, it's only expensive when tracing is
    enabled.

    >
    > Can't you do a tail call and let the function you end
    > up calling do all the callee-saved register pops onto
    > the stack?

    Not sure PPC has such a thing. I'm only a hobby PPC hacker (did it full
    time in another life). If there is such a way, I'll be happy to Ack any
    patches.

    >
    > That's what I did on sparc.
    >

    So that was your secret! ;-)

    -- Steve



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