MIPS: kprobe: Add support.

This patch is based on previous work by Sony and Himanshu Chauhan.

I have done some cleanup and implemented JProbes and KRETPROBES.  The
KRETPROBES part is pretty much copied verbatim from powerpc.  A possible
future enhance might be to factor out the common code.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Cc: Himanshu Chauhan <hschauhan@nulltrace.org>
To: linux-mips@linux-mips.org
To: ananth@in.ibm.com,
To: anil.s.keshavamurthy@intel.com
To: davem@davemloft.net
To: masami.hiramatsu.pt@hitachi.com
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1525/
Patchwork: https://patchwork.linux-mips.org/patch/1530/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/traps.c

@@ -25,6 +25,7 @@
 #include <linux/ptrace.h>
 #include <linux/kgdb.h>
 #include <linux/kdebug.h>
+#include <linux/kprobes.h>
 #include <linux/notifier.h>
 #include <linux/kdb.h>
 
@@ -334,7 +335,7 @@ void show_regs(struct pt_regs *regs)
 	__show_regs((struct pt_regs *)regs);
 }
 
-void show_registers(const struct pt_regs *regs)
+void show_registers(struct pt_regs *regs)
 {
 	const int field = 2 * sizeof(unsigned long);
 
@@ -783,6 +784,25 @@ asmlinkage void do_bp(struct pt_regs *regs)
 	if (bcode >= (1 << 10))
 		bcode >>= 10;
 
+	/*
+	 * notify the kprobe handlers, if instruction is likely to
+	 * pertain to them.
+	 */
+	switch (bcode) {
+	case BRK_KPROBE_BP:
+		if (notify_die(DIE_BREAK, "debug", regs, bcode, 0, 0) == NOTIFY_STOP)
+			return;
+		else
+			break;
+	case BRK_KPROBE_SSTEPBP:
+		if (notify_die(DIE_SSTEPBP, "single_step", regs, bcode, 0, 0) == NOTIFY_STOP)
+			return;
+		else
+			break;
+	default:
+		break;
+	}
+
 	do_trap_or_bp(regs, bcode, "Break");
 	return;