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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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