ARM: kprobes: Add emulation of hint instructions like NOP and WFI

Being able to probe NOP instructions is useful for hard-coding probeable
locations and is used by the kprobes test code.

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

diff --git a/arch/arm/kernel/kprobes-decode.c b/arch/arm/kernel/kprobes-decode.c
index 6bed8b0..03b85ad 100644 (file)
--- a/arch/arm/kernel/kprobes-decode.c
+++ b/arch/arm/kernel/kprobes-decode.c
@@ -1225,6 +1225,30 @@ space_cccc_001x(kprobe_opcode_t insn, struct arch_specific_insn *asi)
        if ((insn & 0x0fb00000) == 0x03000000)
                return prep_emulate_rd12_modify(insn, asi);
 
+       /* hints : cccc 0011 0010 0000 xxxx xxxx xxxx xxxx */
+       if ((insn & 0x0fff0000) == 0x03200000) {
+               unsigned op2 = insn & 0x000000ff;
+               if (op2 == 0x01 || op2 == 0x04) {
+                       /* YIELD : cccc 0011 0010 0000 xxxx xxxx 0000 0001 */
+                       /* SEV   : cccc 0011 0010 0000 xxxx xxxx 0000 0100 */
+                       asi->insn[0] = insn;
+                       asi->insn_handler = emulate_none;
+                       return INSN_GOOD;
+               } else if (op2 <= 0x03) {
+                       /* NOP   : cccc 0011 0010 0000 xxxx xxxx 0000 0000 */
+                       /* WFE   : cccc 0011 0010 0000 xxxx xxxx 0000 0010 */
+                       /* WFI   : cccc 0011 0010 0000 xxxx xxxx 0000 0011 */
+                       /*
+                        * We make WFE and WFI true NOPs to avoid stalls due
+                        * to missing events whilst processing the probe.
+                        */
+                       asi->insn_handler = emulate_nop;
+                       return INSN_GOOD_NO_SLOT;
+               }
+               /* For DBG and unallocated hints it's safest to reject them */
+               return INSN_REJECTED;
+       }
+
        /*
         * MSR   : cccc 0011 0x10 xxxx xxxx xxxx xxxx xxxx
         * ALU op with S bit and Rd == 15 :