[v3 PATCH 1/1] booke/kprobe: make program exception to use one dedicated exception stack

[Chen, Tiejun]

> -----Original Message-----
> From: Scott Wood [mailto:scottwood at freescale.com] 
> Sent: Saturday, July 16, 2011 2:43 AM
> To: Chen, Tiejun
> Cc: Kumar Gala; linuxppc-dev at ozlabs.org
> Subject: Re: [v3 PATCH 1/1] booke/kprobe: make program 
> exception to use one dedicated exception stack
> 
> On Fri, 15 Jul 2011 13:28:15 +0800
> tiejun.chen <tiejun.chen at windriver.com> wrote:
> 
> > Kumar Gala wrote:
> > > I'm still very confused why we need a unique stack frame 
> for kprobe/program exceptions on book-e devices.
> > 
> > Its a bug at least for Book-E.
> 
> But why only booke?  There's nothing booke-specific about the 

I don't mean this is reproduced only on booke, so I use 'at least' carefully to notice we really see this problem on booke.

> stwu instruction.

Please note this root cause to this bug is not related to how to emulate stwu instruction. That should be issued from the overlap between an exception frame and the kprobed function stack frame on booke. Would you like to see that example I showed?

> 
> > And if you'd like to check another topic thread,
> > "[BUG?]3.0-rc4+ftrace+kprobe: set kprobe at instruction 
> 'stwu' lead to 
> > system crash/freeze", you can know this story completely :)
> > 
> > This bug should not be reproduced on PPC64 with the exception 
> > prolog/endlog dedicated to PPC64.
> 
> What if the function you're stepping through is creating a 
> stack frame that is larger than the 288 bytes that get skipped?

>From that bug email looks PPC64 should be good from some feedbacks. So here I think guys who are very familiar with PPC64 can reply this rather than me :)

> 
> > But I have no enough time to check other PPC32 & !BOOKE so I'm not 
> > sure if we should extend this modification.
> 
> Someone should.

This is fine to me.

But currently we have to fix this based on booke firstly.

Tiejun 

> 
> -Scott
> 
>