Re: Re: Re: [RFC][PATCH 2/4 v4] ftrace/x86: Add save_regs fori386 function calls

[Masami Hiramatsu]

(2012/07/17 12:05), Steven Rostedt wrote:
> 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?

It is just FYI :). I rather like your "%sp" enhancement
than current meaningless "%sp" on i386...

However, I think "$stack" is more general and informative
for users, thus, at least perf probe uses it for getting
variables from stack.

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx


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