target-arm: Implement AArch64 CurrentEL sysreg

Implement the CurrentEL sysreg.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>

target-arm/cpu.h

@@ -731,7 +731,8 @@ static inline uint64_t cpreg_to_kvm_id(uint32_t cpregid)
 #define ARM_CP_NOP (ARM_CP_SPECIAL | (1 << 8))
 #define ARM_CP_WFI (ARM_CP_SPECIAL | (2 << 8))
 #define ARM_CP_NZCV (ARM_CP_SPECIAL | (3 << 8))
-#define ARM_LAST_SPECIAL ARM_CP_NZCV
+#define ARM_CP_CURRENTEL (ARM_CP_SPECIAL | (4 << 8))
+#define ARM_LAST_SPECIAL ARM_CP_CURRENTEL
 /* Used only as a terminator for ARMCPRegInfo lists */
 #define ARM_CP_SENTINEL 0xffff
 /* Mask of only the flag bits in a type field */

target-arm/helper.c

@@ -1533,6 +1533,9 @@ static const ARMCPRegInfo v8_cp_reginfo[] = {
       .opc0 = 3, .opc1 = 3, .opc2 = 7, .crn = 0, .crm = 0,
       .access = PL0_R, .type = ARM_CP_CONST,
       .resetvalue = 0x10 },
+    { .name = "CURRENTEL", .state = ARM_CP_STATE_AA64,
+      .opc0 = 3, .opc1 = 0, .opc2 = 2, .crn = 4, .crm = 2,
+      .access = PL1_R, .type = ARM_CP_CURRENTEL },
     REGINFO_SENTINEL
 };
 

target-arm/translate-a64.c

@@ -1231,6 +1231,13 @@ static void handle_sys(DisasContext *s, uint32_t insn, bool isread,
             gen_set_nzcv(tcg_rt);
         }
         return;
+    case ARM_CP_CURRENTEL:
+        /* Reads as current EL value from pstate, which is
+         * guaranteed to be constant by the tb flags.
+         */
+        tcg_rt = cpu_reg(s, rt);
+        tcg_gen_movi_i64(tcg_rt, s->current_pl << 2);
+        return;
     default:
         break;
     }