Re: x86_64 frame pointer via thread context

[Dave Jiang <djiang@mvista.com>]

Dave Jiang wrote:
> Jan Engelhardt wrote:
> 
>>>> Am I doing something wrong, or is this intended to be this way on
>>>> x86_64, or is something incorrect in the kernel? This method works
>>>> fine on i386. Thanks for any help!
>>>
>>>
>>> I just tested your program on SLES9 with updated kernel and RBP
>>> looks correct to me. Probably something is wrong with your user space
>>> includes or your compiler.
>>
>>
>>
>> Note that there is -fomit-frame-pointer which might give different 
>> results than without the option (or explicitly -fno-omit-frame-pointer).
>>
>>
>> Jan Engelhardt
> 
> 
> I had somebody else test it on FC4 and he observed the same issue. It 
> may be timing sensitive? Both platforms tested are em64t based so I'm 
> not sure if on amd64 platforms it varies or not.....
> 
> And you definitely have to include the -fno-omit-frame-pointer. x86_64 
> gcc by default has -fomit-frame-pointer on and without explicitly 
> stating that you want frame pointer you won't get it in rBP.
> 
> It is possible that userspace or toolchain may be suspect, However, why 
> is the value bad in kernel space when rBP from pt_regs is dumped?
> 
> 

One additional note. The app dumps the rBP for two threads. One looks 
okay, and the other gives 0xffffffff.


-- 
Dave

------------------------------------------------------
Dave Jiang
Software Engineer          Phone: (480) 517-0372
MontaVista Software, Inc.    Fax: (480) 517-0262
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Tempe, AZ  85282          mailto:djiang@mvista.com
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