[PATCH v3 3/6] powerpc/64s: Blacklist system_call() and system_call_common() from kprobes

[Naveen N. Rao]

On 2017/06/22 11:08PM, Nicholas Piggin wrote:
> On Thu, 22 Jun 2017 21:07:46 +1000
> Michael Ellerman <mpe at ellerman.id.au> wrote:
> 
> > Nicholas Piggin <npiggin at gmail.com> writes:
> > 
> > > On Thu, 22 Jun 2017 00:08:39 +0530
> > > "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com> wrote:
> > >  
> > >> Convert some of the symbols into private symbols and blacklist
> > >> system_call_common() and system_call() from kprobes. We can't take a
> > >> trap at parts of these functions as either MSR_RI is unset or the kernel
> > >> stack pointer is not yet setup.
> > >> 
> > >> Reviewed-by: Masami Hiramatsu <mhiramat at kernel.org>
> > >> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>  
> > >
> > > I don't have a problem with this bunch of system call labels
> > > going private. They've never added much for me in profiles.
> > >
> > > Reviewed-by: Nicholas Piggin <npiggin at gmail.com>

Thanks for the review.

> > >
> > > Semi-related question, why is system_call: where it is?  
> > 
> > Ancient history.
> > 
> > We used to have:
> > 
> > 	bne	syscall_dotrace
> > syscall_dotrace_cont:
> > 	cmpldi	0,r0,NR_syscalls
> > 	bge-	syscall_enosys
> > 
> > system_call:			/* label this so stack traces look sane */
> > 
> > 
> > So it was there to hide syscall_dotrace_cont from back traces.
> > 
> > But we made syscall_dotrace_cont local in 2012 and then removed it
> > entirely in 2015.
> > 
> > > Should we move it up to right after the mtmsrd / wrteei instruction?
> > > (obviously for another patch). It's pretty common to get PMU
> > > interrupts coming in right after mtmsr and this makes profiles split
> > > the syscall into two which is annoying.  
> > 
> > Move it wherever makes sense and gives good back traces.
> 
> I'd be in favour of moving it to right after the interurpt enable.
> I suppose you'd want a separate patch for that though. But we could
> put it in this series since we're changing a lot of labels.

Sure, I'll add a patch that does that.

- Naveen