Re: [RFC][PATCH 05/13 v2] ftrace/x86: Add separate function to save regs

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(2012/06/15 20:33), Steven Rostedt wrote:
> On Fri, 2012-06-15 at 17:15 +0900, Masami Hiramatsu wrote:
> 
>>> It is OK for an arch to pass NULL regs. All function trace users that
>>> require regs passing must add the flag FTRACE_OPS_FL_SAVE_REGS when
>>> registering the ftrace_ops and either check if regs is not NULL or
>>> check if ARCH_SUPPORTS_FTRACE_SAVE_REGS. If the arch supports passing
>>> regs it will set this macro and pass regs for ops that request them.
>>> All other archs will just pass NULL.
>>
>> Hmm, so would you mean that user is responsible for checking
>> whether the arch supports save_regs or not?
>> I would rather like ftrace to check it as my patch has done.
>> I think ARCH_SUPPORTS_FTRACE_SAVE_REGS macro checking in all
>> handler code is something like odd...
> 
> I was thinking of routines that may or may not use regs. Actually, I was
> thinking about perf in general, that could use regs if supported, or get
> its own set.
> 
> But I agree that it may not be the best for those that must have regs.
> 
> Perhaps we could add another flag:
> 
> FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED
> 
> Where it wont error out if you have this set. But if you just pass in
> FTRACE_OPS_FL_SAVE_REGS (as kprobes does) it will fail.
> 
> How's that sound?

Yeah, that's good for me. :)

Thank you,

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