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    SubjectRe: [PATCH -v4 4/9] tracing: add static function tracer support for MIPS
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    Hi,

    On Thu, 2009-10-22 at 11:34 -0700, David Daney wrote:
    > Wu Zhangjin wrote:
    > > On Wed, 2009-10-21 at 11:24 -0400, Steven Rostedt wrote:
    > [...]
    > >>> +
    > >>> +NESTED(_mcount, PT_SIZE, ra)
    > >>> + RESTORE_SP_FOR_32BIT
    > >>> + PTR_LA t0, ftrace_stub
    > >>> + PTR_L t1, ftrace_trace_function /* please don't use t1 later, safe? */
    > >> Is t0 and t1 safe for mcount to use? Remember, mcount does not follow
    > >> the dynamics of C function ABI.
    > >
    > > So, perhaps we can use the saved registers(a0,a1...) instead.
    > >
    >
    > a0..a7 may not always be saved.

    I mean I have saved/restored them as the _mcount of /lib/libc.so.6 for
    MIPS did, so I can use them safely.

    >
    > You can use at, v0, v1 and all the temporary registers. Note that for
    > the 64-bit ABIs sometimes the names t0-t4 shadow a4-a7. So for a 64-bit
    > kernel, you can use: $1, $2, $3, $12, $13, $14, $15, $24, $25, noting
    > that at == $1 and contains the callers ra. For a 32-bit kernel you can
    > add $8, $9, $10, and $11
    >

    In a generic function, they should be okay, but _mcount is a little
    specific. so, Not sure these rules are suitable to it or not.

    > This whole thing seems a little fragile.
    >
    > I think it might be a good idea to get input from Richard Sandiford,
    > and/or Adam Nemet about this approach (so I add them to the CC).
    >
    > This e-mail thread starts here:
    >
    > http://www.linux-mips.org/archives/linux-mips/2009-10/msg00286.html
    >
    > and here:
    >
    > http://www.linux-mips.org/archives/linux-mips/2009-10/msg00290.html

    looking forward to their reply, thanks!

    Regards!
    Wu Zhangjin



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