ARM: kprobes: Add bx_write_pc()

This writes a value to PC, with interworking. I.e. switches to Thumb or
ARM mode depending on the state of the least significant bit.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/arch/arm/kernel/kprobes.h b/arch/arm/kernel/kprobes.h
index 36e07684fe08..12627a376bf6 100644
--- a/arch/arm/kernel/kprobes.h
+++ b/arch/arm/kernel/kprobes.h
@@ -95,6 +95,20 @@ static inline unsigned long it_advance(unsigned long cpsr)
         return cpsr;
 }
 
+static inline void __kprobes bx_write_pc(long pcv, struct pt_regs *regs)
+{
+        long cpsr = regs->ARM_cpsr;
+        if (pcv & 0x1) {
+                cpsr |= PSR_T_BIT;
+                pcv &= ~0x1;
+        } else {
+                cpsr &= ~PSR_T_BIT;
+                pcv &= ~0x2;    /* Avoid UNPREDICTABLE address allignment */
+        }
+        regs->ARM_cpsr = cpsr;
+        regs->ARM_pc = pcv;
+}
+
 void __kprobes kprobe_simulate_nop(struct kprobe *p, struct pt_regs *regs);
 void __kprobes kprobe_emulate_none(struct kprobe *p, struct pt_regs *regs);