Re: want to clarify powerpc assembly conventions in head.S and entry.S

[Chris Friesen]

Benjamin Herrenschmidt wrote:
> > You knew this was coming...  What's special about syscalls?  There's the 
> > r3 thing, but other than that...
>
> The whole codepath is a bit different, there's the syscall trace,
> we can avoid saving much more registers are syscalls are function
> calls and so can clobber the non volatiles, etc...

It appears that we always enter the kernel via "transfer_to_handler", 
and return via "ret_from_except".  Is this true? (I'm running on at 
least a 74xx chip.)

I want to insert two new bits of code, one that gets called before the 
exception handler when we drop from userspace to kernelspace, and one as 
late as possible before going back to userspace.  I need to catch 
syscalls, interrupts, exceptions, everything.

The entry one I planned on putting in "transfer_to_handler", just before 
"addi   r11,r1,STACK_FRAME_OVERHEAD".

I was planning on putting the exit one just after the "restore_user" 
label.  Will this catch all possible returns to userspace?

Thanks,

Chris
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