target/arm: Implement v8M VLLDM and VLSTM

For v8M the instructions VLLDM and VLSTM support lazy saving
and restoring of the secure floating-point registers. Even
if the floating point extension is not implemented, these
instructions must act as NOPs in Secure state, so they can
be used as part of the secure-to-nonsecure call sequence.

Fixes: https://bugs.launchpad.net/qemu/+bug/1768295
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180503105730.5958-1-peter.maydell@linaro.org

target/arm/translate.c

@@ -10795,8 +10795,23 @@ static void disas_thumb2_insn(DisasContext *s, uint32_t insn)
         /* Coprocessor.  */
         if (arm_dc_feature(s, ARM_FEATURE_M)) {
             /* We don't currently implement M profile FP support,
-             * so this entire space should give a NOCP fault.
+             * so this entire space should give a NOCP fault, with
+             * the exception of the v8M VLLDM and VLSTM insns, which
+             * must be NOPs in Secure state and UNDEF in Nonsecure state.
              */
+            if (arm_dc_feature(s, ARM_FEATURE_V8) &&
+                (insn & 0xffa00f00) == 0xec200a00) {
+                /* 0b1110_1100_0x1x_xxxx_xxxx_1010_xxxx_xxxx
+                 *  - VLLDM, VLSTM
+                 * We choose to UNDEF if the RAZ bits are non-zero.
+                 */
+                if (!s->v8m_secure || (insn & 0x0040f0ff)) {
+                    goto illegal_op;
+                }
+                /* Just NOP since FP support is not implemented */
+                break;
+            }
+            /* All other insns: NOCP */
             gen_exception_insn(s, 4, EXCP_NOCP, syn_uncategorized(),
                                default_exception_el(s));
             break;