target/arm: Adjust FPCR_MASK for FZ16

When support for FZ16 was added, we failed to include the bit
within FPCR_MASK, which means that it could never be set.
Continue to zero FZ16 when ARMv8.2-FP16 is not enabled.

Fixes: d81ce0ef
Cc: qemu-stable@nongnu.org (3.0.1)
Reported-by: NLaurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NLaurent Desnogues <laurent.desnogues@gmail.com>
Tested-by: NLaurent Desnogues <laurent.desnogues@gmail.com>
Message-id: 20180810193129.1556-2-richard.henderson@linaro.org
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target/arm/cpu.h

@@ -1269,7 +1269,7 @@ void vfp_set_fpscr(CPUARMState *env, uint32_t val);
  * we store the underlying state in fpscr and just mask on read/write.
  */
 #define FPSR_MASK 0xf800009f
-#define FPCR_MASK 0x07f79f00
+#define FPCR_MASK 0x07ff9f00
 
 #define FPCR_FZ16   (1 << 19)   /* ARMv8.2+, FP16 flush-to-zero */
 #define FPCR_FZ     (1 << 24)   /* Flush-to-zero enable bit */

target/arm/helper.c

@@ -11349,6 +11349,11 @@ void HELPER(vfp_set_fpscr)(CPUARMState *env, uint32_t val)
     int i;
     uint32_t changed;
 
+    /* When ARMv8.2-FP16 is not supported, FZ16 is RES0.  */
+    if (!arm_feature(env, ARM_FEATURE_V8_FP16)) {
+        val &= ~FPCR_FZ16;
+    }
+
     changed = env->vfp.xregs[ARM_VFP_FPSCR];
     env->vfp.xregs[ARM_VFP_FPSCR] = (val & 0xffc8ffff);
     env->vfp.vec_len = (val >> 16) & 7;