target-arm: A64: expand decoding skeleton for system instructions

Decode the various kinds of system instructions:
 hints (HINT), which include NOP, YIELD, WFE, WFI, SEV, SEL
 sync instructions, which include CLREX, DSB, DMB, ISB
 msr_i, which move immediate to processor state field
 sys, which include all SYS and SYSL instructions
 msr, which move from a gp register to a system register
 mrs, which move from a system register to a gp register

Provide implementations where they are trivial nops.

Signed-off-by: Claudio Fontana <claudio.fontana@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>

target-arm/translate-a64.c

@@ -190,12 +190,139 @@ static void disas_cond_b_imm(DisasContext *s, uint32_t insn)
     unsupported_encoding(s, insn);
 }
 
-/* System */
+/* C5.6.68 HINT */
-static void disas_system(DisasContext *s, uint32_t insn)
+static void handle_hint(DisasContext *s, uint32_t insn,
+                        unsigned int op1, unsigned int op2, unsigned int crm)
+{
+    unsigned int selector = crm << 3 | op2;
+
+    if (op1 != 3) {
+        unallocated_encoding(s);
+        return;
+    }
+
+    switch (selector) {
+    case 0: /* NOP */
+        return;
+    case 1: /* YIELD */
+    case 2: /* WFE */
+    case 3: /* WFI */
+    case 4: /* SEV */
+    case 5: /* SEVL */
+        /* we treat all as NOP at least for now */
+        return;
+    default:
+        /* default specified as NOP equivalent */
+        return;
+    }
+}
+
+/* CLREX, DSB, DMB, ISB */
+static void handle_sync(DisasContext *s, uint32_t insn,
+                        unsigned int op1, unsigned int op2, unsigned int crm)
+{
+    if (op1 != 3) {
+        unallocated_encoding(s);
+        return;
+    }
+
+    switch (op2) {
+    case 2: /* CLREX */
+        unsupported_encoding(s, insn);
+        return;
+    case 4: /* DSB */
+    case 5: /* DMB */
+    case 6: /* ISB */
+        /* We don't emulate caches so barriers are no-ops */
+        return;
+    default:
+        unallocated_encoding(s);
+        return;
+    }
+}
+
+/* C5.6.130 MSR (immediate) - move immediate to processor state field */
+static void handle_msr_i(DisasContext *s, uint32_t insn,
+                         unsigned int op1, unsigned int op2, unsigned int crm)
 {
     unsupported_encoding(s, insn);
 }
 
+/* C5.6.204 SYS */
+static void handle_sys(DisasContext *s, uint32_t insn, unsigned int l,
+                       unsigned int op1, unsigned int op2,
+                       unsigned int crn, unsigned int crm, unsigned int rt)
+{
+    unsupported_encoding(s, insn);
+}
+
+/* C5.6.129 MRS - move from system register */
+static void handle_mrs(DisasContext *s, uint32_t insn, unsigned int op0,
+                       unsigned int op1, unsigned int op2,
+                       unsigned int crn, unsigned int crm, unsigned int rt)
+{
+    unsupported_encoding(s, insn);
+}
+
+/* C5.6.131 MSR (register) - move to system register */
+static void handle_msr(DisasContext *s, uint32_t insn, unsigned int op0,
+                       unsigned int op1, unsigned int op2,
+                       unsigned int crn, unsigned int crm, unsigned int rt)
+{
+    unsupported_encoding(s, insn);
+}
+
+/* C3.2.4 System
+ *  31                 22 21  20 19 18 16 15   12 11    8 7   5 4    0
+ * +---------------------+---+-----+-----+-------+-------+-----+------+
+ * | 1 1 0 1 0 1 0 1 0 0 | L | op0 | op1 |  CRn  |  CRm  | op2 |  Rt  |
+ * +---------------------+---+-----+-----+-------+-------+-----+------+
+ */
+static void disas_system(DisasContext *s, uint32_t insn)
+{
+    unsigned int l, op0, op1, crn, crm, op2, rt;
+    l = extract32(insn, 21, 1);
+    op0 = extract32(insn, 19, 2);
+    op1 = extract32(insn, 16, 3);
+    crn = extract32(insn, 12, 4);
+    crm = extract32(insn, 8, 4);
+    op2 = extract32(insn, 5, 3);
+    rt = extract32(insn, 0, 5);
+
+    if (op0 == 0) {
+        if (l || rt != 31) {
+            unallocated_encoding(s);
+            return;
+        }
+        switch (crn) {
+        case 2: /* C5.6.68 HINT */
+            handle_hint(s, insn, op1, op2, crm);
+            break;
+        case 3: /* CLREX, DSB, DMB, ISB */
+            handle_sync(s, insn, op1, op2, crm);
+            break;
+        case 4: /* C5.6.130 MSR (immediate) */
+            handle_msr_i(s, insn, op1, op2, crm);
+            break;
+        default:
+            unallocated_encoding(s);
+            break;
+        }
+        return;
+    }
+
+    if (op0 == 1) {
+        /* C5.6.204 SYS */
+        handle_sys(s, insn, l, op1, op2, crn, crm, rt);
+    } else if (l) { /* op0 > 1 */
+        /* C5.6.129 MRS - move from system register */
+        handle_mrs(s, insn, op0, op1, op2, crn, crm, rt);
+    } else {
+        /* C5.6.131 MSR (register) - move to system register */
+        handle_msr(s, insn, op0, op1, op2, crn, crm, rt);
+    }
+}
+
 /* Exception generation */
 static void disas_exc(DisasContext *s, uint32_t insn)
 {