On Sat, 16 Jul 2011 03:25:47 +0000
"Chen, Tiejun" [off-list ref] wrote:

quoted

-----Original Message-----
From: Scott Wood [mailto:scottwood@freescale.com] 
Sent: Saturday, July 16, 2011 2:43 AM
To: Chen, Tiejun
Cc: Kumar Gala; linuxppc-dev@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 [off-list ref] wrote:

quoted

Kumar Gala wrote:

quoted

I'm still very confused why we need a unique stack frame 

for kprobe/program exceptions on book-e devices.

quoted

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.

quoted

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?

As I understand it, the problem comes from the fact that stwu combines the
creation of a stack frame with storing into that stack frame.  If they were
separate instructions you'd have a new exception frame at a lower address
by the time you actually store to the non-exception frame.

-Scott