[v3 PATCH 1/1] booke/kprobe: make program exception to use one dedicated exception stack
scottwood at freescale.com
Fri Jul 15 01:53:52 EST 2011
On Thu, 14 Jul 2011 08:27:44 -0500
Kumar Gala <galak at kernel.crashing.org> wrote:
> On Jul 11, 2011, at 6:31 AM, Tiejun Chen wrote:
> > When kprobe these operations such as store-and-update-word for SP(r1),
> > stwu r1, -A(r1)
> > The program exception is triggered, and PPC always allocate an exception frame
> > as shown as the follows:
> > old r1 ----------
> > ...
> > nip
> > gpr ~ gpr
> > gpr <--------- old r1 is stored.
> > gpr
> > -------- <--------- pr_regs @offset 16 bytes
> > padding
> > STACK_FRAME_REGS_MARKER
> > LR
> > back chain
> > new r1 ----------
> > Then emulate_step() will emulate this instruction, 'stwu'. Actually its
> > equivalent to:
> > 1> Update pr_regs->gpr = mem[old r1 + (-A)]
> > 2> stw [old r1], mem[old r1 + (-A)]
> > Please notice the stack based on new r1 may be covered with mem[old r1
> > +(-A)] when addr[old r1 + (-A)] < addr[old r1 + sizeof(an exception frame0].
> > So the above 2# operation will overwirte something to break this exception
> > frame then unexpected kernel problem will be issued.
> > So looks we have to implement independed interrupt stack for PPC program
> > exception when CONFIG_BOOKE is enabled. Here we can use
> > EXC_LEVEL_EXCEPTION_PROLOG to replace original NORMAL_EXCEPTION_PROLOG
> > for program exception if CONFIG_BOOKE. Then its always safe for kprobe
> > with independed exc stack from one pre-allocated and dedicated thread_info.
> > Actually this is just waht we did for critical/machine check exceptions
> > on PPC.
> > Signed-off-by: Tiejun Chen <tiejun.chen at windriver.com>
> > ---
> I'm still very confused why we need a unique stack frame for kprobe/program exceptions on book-e devices.
I don't know why it's booke-specific (or why they're emulating rather than
using single-step), but the problem is trying to emulate an instruction
that's expanding the non-exception stack into the area that the exception
handler is sitting on, and writing to that new stack area.
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