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
2141 E Broadway Rd, St 108   Web: www.mvista.com
Tempe, AZ  85282          mailto:djiang@mvista.com
------------------------------------------------------

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