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powerpc/kprobes: Update optprobes to use emulate_update_regs() 

Optprobes depended on an updated regs->nip from analyse_instr() to
identify the location to branch back from the optprobes trampoline.
However, since commit 3cdfcbfd32 ("powerpc: Change analyse_instr so
it doesn't modify *regs"), analyse_instr() doesn't update the registers
anymore.  Due to this, we end up branching back from the optprobes
trampoline to the same branch into the trampoline resulting in a loop.

Fix this by calling out to emulate_update_regs() before using the nip.
Additionally, explicitly compare the return value from analyse_instr()
to 1, rather than just checking for !0 so as to guard against any
future changes to analyse_instr() that may result in -1 being returned
in more scenarios.

Fixes: 3cdfcbfd32 ("powerpc: Change analyse_instr so it doesn't modify *regs")
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Naveen N. Rao 2017-09-15 15:38:21 +05:30 committed by Michael Ellerman
parent b134165ead
commit 8afafa6fba
1 changed files with 3 additions and 1 deletions
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4
arch/powerpc/kernel/optprobes.c
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@ -104,8 +104,10 @@ static unsigned long can_optimize(struct kprobe *p)
* and that can be emulated.
*/
if (!is_conditional_branch(*p->ainsn.insn) &&
analyse_instr(&op, &regs, *p->ainsn.insn))
analyse_instr(&op, &regs, *p->ainsn.insn) == 1) {
emulate_update_regs(&regs, &op);
nip = regs.nip;
}
return nip;
}