Re: x86_64 frame pointer via thread context

[Dave Jiang <djiang@mvista.com>]

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?


-- 
Dave

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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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