powerpc/booke: Add kprobes support for booke style processors

This patch is based on work done by Madhvesh. R. Sulibhavi back in
March 2007.

We refactor some of the single step handling since it differs between
"classic" and "booke" powerpc cores.

Signed-off-by: Kumar Gala <[e-mail]>

Documentation/kprobes.txt

···
 - ia64 (Does not support probes on instruction slot1.)
 - sparc64 (Return probes not yet implemented.)
 - arm
+- ppc
 
 3. Configuring Kprobes
 

arch/powerpc/kernel/kprobes.c

···
 #include <asm/cacheflush.h>
 #include <asm/sstep.h>
 #include <asm/uaccess.h>
+#include <asm/system.h>
+
+#ifdef CONFIG_BOOKE
+#define MSR_SINGLESTEP	(MSR_DE)
+#else
+#define MSR_SINGLESTEP	(MSR_SE)
+#endif
 
 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
···
 		ret = -EINVAL;
 	}
 
-	/* insn must be on a special executable page on ppc64 */
+	/* insn must be on a special executable page on ppc64.  This is
+	 * not explicitly required on ppc32 (right now), but it doesn't hurt */
 	if (!ret) {
 		p->ainsn.insn = get_insn_slot();
 		if (!p->ainsn.insn)
···
 	 * possible we'd get the single step reported for an exception handler
 	 * like Decrementer or External Interrupt */
 	regs->msr &= ~MSR_EE;
-	regs->msr |= MSR_SE;
+	regs->msr |= MSR_SINGLESTEP;
+#ifdef CONFIG_BOOKE
+	regs->msr &= ~MSR_CE;
+	mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) | DBCR0_IC | DBCR0_IDM);
+#endif
 
 	/*
 	 * On powerpc we should single step on the original
···
 			kprobe_opcode_t insn = *p->ainsn.insn;
 			if (kcb->kprobe_status == KPROBE_HIT_SS &&
 					is_trap(insn)) {
-				regs->msr &= ~MSR_SE;
+				/* Turn off 'trace' bits */
+				regs->msr &= ~MSR_SINGLESTEP;
 				regs->msr |= kcb->kprobe_saved_msr;
 				goto no_kprobe;
 			}
···
 
 	/*
 	 * if somebody else is singlestepping across a probe point, msr
-	 * will have SE set, in which case, continue the remaining processing
+	 * will have DE/SE set, in which case, continue the remaining processing
 	 * of do_debug, as if this is not a probe hit.
 	 */
-	if (regs->msr & MSR_SE)
+	if (regs->msr & MSR_SINGLESTEP)
 		return 0;
 
 	return 1;
···
 		 * normal page fault.
 		 */
 		regs->nip = (unsigned long)cur->addr;
-		regs->msr &= ~MSR_SE;
+		regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 		regs->msr |= kcb->kprobe_saved_msr;
 		if (kcb->kprobe_status == KPROBE_REENTER)
 			restore_previous_kprobe(kcb);

arch/powerpc/kernel/traps.c

···
 
 #if defined(CONFIG_40x) || defined(CONFIG_BOOKE)
 
-void DebugException(struct pt_regs *regs, unsigned long debug_status)
+void __kprobes DebugException(struct pt_regs *regs, unsigned long debug_status)
 {
 	if (debug_status & DBSR_IC) {	/* instruction completion */
 		regs->msr &= ~MSR_DE;
+
+		/* Disable instruction completion */
+		mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) & ~DBCR0_IC);
+		/* Clear the instruction completion event */
+		mtspr(SPRN_DBSR, DBSR_IC);
+
+		if (notify_die(DIE_SSTEP, "single_step", regs, 5,
+			       5, SIGTRAP) == NOTIFY_STOP) {
+			return;
+		}
+
+		if (debugger_sstep(regs))
+			return;
+
 		if (user_mode(regs)) {
 			current->thread.dbcr0 &= ~DBCR0_IC;
-		} else {
-			/* Disable instruction completion */
-			mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) & ~DBCR0_IC);
-			/* Clear the instruction completion event */
-			mtspr(SPRN_DBSR, DBSR_IC);
-			if (debugger_sstep(regs))
-				return;
 		}
-		_exception(SIGTRAP, regs, TRAP_TRACE, 0);
+
+		_exception(SIGTRAP, regs, TRAP_TRACE, regs->nip);
 	}
 }
 #endif /* CONFIG_4xx || CONFIG_BOOKE */