On Jul 11, 2011, at 6:31 AM, Tiejun Chen wrote:

When kprobe these operations such as store-and-update-word for SP(r1),
=20
stwu r1, -A(r1)
=20
The program exception is triggered, and PPC always allocate an =

exception frame

as shown as the follows:
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old r1 ----------
        ...
        nip
        gpr[2] ~ gpr[31]
        gpr[1] <--------- old r1 is stored.
        gpr[0]
      -------- <--------- 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[1] =3D mem[old r1 + (-A)]
2> stw [old r1], mem[old r1 + (-A)]
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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.
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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.
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Signed-off-by: Tiejun Chen <redacted>
---

I'm still very confused why we need a unique stack frame for =
kprobe/program exceptions on book-e devices.

Can you explain this further.

- k