MIPS Kprobes: Support branch instructions probing
This patch provides support for kprobes on branch instructions. The branch
instruction at the probed address is actually emulated and not executed
out-of-line like other normal instructions. Instead the delay-slot instruction
is copied and single stepped out of line.
At the time of probe hit, the original branch instruction is evaluated
and the target cp0_epc is computed similar to compute_retrun_epc(). It
is also checked if the delay slot instruction can be skipped, which is
true if there is a NOP in delay slot or branch is taken in case of
branch likely instructions. Once the delay slot instruction is single
stepped the normal execution resume with the cp0_epc updated the earlier
computed cp0_epc as per the branch instructions.
Signed-off-by: Maneesh Soni <manesoni@cisco.com>
Signed-off-by: Victor Kamensky <kamensky@cisco.com>
Cc: David Daney <david.daney@cavium.com>
Cc: ananth@in.ibm.com
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2914/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/include/asm/kprobes.h b/arch/mips/include/asm/kprobes.h
index e6ea4d4..1fbbca0 100644
--- a/arch/mips/include/asm/kprobes.h
+++ b/arch/mips/include/asm/kprobes.h
@@ -74,6 +74,8 @@
: MAX_JPROBES_STACK_SIZE)
+#define SKIP_DELAYSLOT 0x0001
+
/* per-cpu kprobe control block */
struct kprobe_ctlblk {
unsigned long kprobe_status;
@@ -82,6 +84,9 @@
unsigned long kprobe_saved_epc;
unsigned long jprobe_saved_sp;
struct pt_regs jprobe_saved_regs;
+ /* Per-thread fields, used while emulating branches */
+ unsigned long flags;
+ unsigned long target_epc;
u8 jprobes_stack[MAX_JPROBES_STACK_SIZE];
struct prev_kprobe prev_kprobe;
};