target/s390x: Fix CLM with M3=0

When the mask is zero, access exceptions should still be recognized for
1 byte at the second-operand address. CC should be set to 0.

Cc: qemu-stable@nongnu.org
Fixes: defb0e3 ("s390x: Implement opcode helpers")
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230724082032.66864-3-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

target/s390x/tcg/mem_helper.c

@@ -667,6 +667,11 @@ uint32_t HELPER(clm)(CPUS390XState *env, uint32_t r1, uint32_t mask,
     HELPER_LOG("%s: r1 0x%x mask 0x%x addr 0x%" PRIx64 "\n", __func__, r1,
                mask, addr);
 
+    if (!mask) {
+        /* Recognize access exceptions for the first byte */
+        probe_read(env, addr, 1, cpu_mmu_index(env, false), ra);
+    }
+
     while (mask) {
         if (mask & 8) {
             uint8_t d = cpu_ldub_data_ra(env, addr, ra);