[SPARC64]: Add kretprobe support.

Passes the smoke tests at least, powerpc implementation was used
as a guide.
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc64/kernel/kprobes.c

@@ -480,8 +480,117 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 	return 0;
 }
 
-/* architecture specific initialization */
-int arch_init_kprobes(void)
+/* Called with kretprobe_lock held.  The value stored in the return
+ * address register is actually 2 instructions before where the
+ * callee will return to.  Sequences usually look something like this
+ *
+ *		call	some_function	<--- return register points here
+ *		 nop			<--- call delay slot
+ *		whatever		<--- where callee returns to
+ *
+ * To keep trampoline_probe_handler logic simpler, we normalize the
+ * value kept in ri->ret_addr so we don't need to keep adjusting it
+ * back and forth.
+ */
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
+				      struct pt_regs *regs)
+{
+	ri->ret_addr = (kprobe_opcode_t *)(regs->u_regs[UREG_RETPC] + 8);
+
+	/* Replace the return addr with trampoline addr */
+	regs->u_regs[UREG_RETPC] =
+		((unsigned long)kretprobe_trampoline) - 8;
+}
+
+/*
+ * Called when the probe at kretprobe trampoline is hit
+ */
+int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kretprobe_instance *ri = NULL;
+	struct hlist_head *head, empty_rp;
+	struct hlist_node *node, *tmp;
+	unsigned long flags, orig_ret_address = 0;
+	unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
+
+	INIT_HLIST_HEAD(&empty_rp);
+	spin_lock_irqsave(&kretprobe_lock, flags);
+	head = kretprobe_inst_table_head(current);
+
+	/*
+	 * It is possible to have multiple instances associated with a given
+	 * task either because an multiple functions in the call path
+	 * have a return probe installed on them, and/or more then one return
+	 * return probe was registered for a target function.
+	 *
+	 * We can handle this because:
+	 *     - instances are always inserted at the head of the list
+	 *     - when multiple return probes are registered for the same
+	 *       function, the first instance's ret_addr will point to the
+	 *       real return address, and all the rest will point to
+	 *       kretprobe_trampoline
+	 */
+	hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
+		if (ri->task != current)
+			/* another task is sharing our hash bucket */
+			continue;
+
+		if (ri->rp && ri->rp->handler)
+			ri->rp->handler(ri, regs);
+
+		orig_ret_address = (unsigned long)ri->ret_addr;
+		recycle_rp_inst(ri, &empty_rp);
+
+		if (orig_ret_address != trampoline_address)
+			/*
+			 * This is the real return address. Any other
+			 * instances associated with this task are for
+			 * other calls deeper on the call stack
+			 */
+			break;
+	}
+
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
+	regs->tpc = orig_ret_address;
+	regs->tnpc = orig_ret_address + 4;
+
+	reset_current_kprobe();
+	spin_unlock_irqrestore(&kretprobe_lock, flags);
+	preempt_enable_no_resched();
+
+	hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
+		hlist_del(&ri->hlist);
+		kfree(ri);
+	}
+	/*
+	 * By returning a non-zero value, we are telling
+	 * kprobe_handler() that we don't want the post_handler
+	 * to run (and have re-enabled preemption)
+	 */
+	return 1;
+}
+
+void kretprobe_trampoline_holder(void)
+{
+	asm volatile(".global kretprobe_trampoline\n"
+		     "kretprobe_trampoline:\n"
+		     "\tnop\n"
+		     "\tnop\n");
+}
+static struct kprobe trampoline_p = {
+	.addr = (kprobe_opcode_t *) &kretprobe_trampoline,
+	.pre_handler = trampoline_probe_handler
+};
+
+int __init arch_init_kprobes(void)
 {
+	return register_kprobe(&trampoline_p);
+}
+
+int __kprobes arch_trampoline_kprobe(struct kprobe *p)
+{
+	if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
+		return 1;
+
 	return 0;
 }

include/asm-sparc64/kprobes.h

@@ -14,11 +14,15 @@ typedef u32 kprobe_opcode_t;
 
 #define arch_remove_kprobe(p)	do {} while (0)
 
+#define ARCH_SUPPORTS_KRETPROBES
+
 #define flush_insn_slot(p)		\
 do { 	flushi(&(p)->ainsn.insn[0]);	\
 	flushi(&(p)->ainsn.insn[1]);	\
 } while (0)
 
+void kretprobe_trampoline(void);
+
 /* Architecture specific copy of original instruction*/
 struct arch_specific_insn {
 	/* copy of the original instruction */