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    SubjectRe: Re: [RFC][PATCH 2/4 v4] ftrace/x86: Add save_regs for i386 function calls
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    On Tue, 2012-07-17 at 11:08 +0900, Masami Hiramatsu wrote:

    > > I found that regs_get_register() doesn't honor this either. Thus,
    > > kprobes in tracing gets this:
    > >
    > > # echo 'p:ftrace sys_read+4 s=%sp' > /debug/tracing/kprobe_events
    > > # echo 1 > /debug/tracing/events/kprobes/enable
    > > # cat trace
    > > sshd-1345 [000] d... 489.117168: ftrace: (sys_read+0x4/0x70) s=b7e96768
    > > sshd-1345 [000] d... 489.117191: ftrace: (sys_read+0x4/0x70) s=b7e96768
    > > cat-1447 [000] d... 489.117392: ftrace: (sys_read+0x4/0x70) s=5a7
    > > cat-1447 [001] d... 489.118023: ftrace: (sys_read+0x4/0x70) s=b77ad05f
    > > less-1448 [000] d... 489.118079: ftrace: (sys_read+0x4/0x70) s=b7762e06
    > > less-1448 [000] d... 489.118117: ftrace: (sys_read+0x4/0x70) s=b7764970
    > >
    >
    > Yes, that is by design, since I made it so. :)
    > Instead of %sp, kprobe tracer provides $stack special argument
    > for stack address, because "sp" is not always means the stack
    > address on every arch.

    But is that useful? Wouldn't the actual stack pointer be more
    informative?

    -- Steve




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