target-arm: A64: Correctly fault FP/Neon if CPACR.FPEN set

For the A64 instruction set, the only FP/Neon disable trap
is the CPACR FPEN bits, which may indicate "enabled", "disabled"
or "disabled for EL0". Add a bit to the AArch64 tb flags indicating
whether FP/Neon access is currently enabled and make the decoder
emit code to raise exceptions on use of FP/Neon insns if it is not.

We use a new flag in DisasContext rather than borrowing the
existing vfp_enabled flag because the A32/T32 decoder is going
to need both.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
---
I'm aware this is a rather hard to review patch; sorry.
I have done an exhaustive check that we have fp access checks
in all code paths with the aid of the assertions added in the
next patch plus the code-coverage hack patch I posted to the
list earlier.

This patch is correct as of
09e037354 target-arm: A64: Add saturating accumulate ops (USQADD/SUQADD)
which was the last of the Neon insns to be added, so assuming
no refactoring of the code it should be fine.

1 files changed, 9 insertions, 0 deletions

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 7a48241..72c4c7a 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -1108,6 +1108,8 @@ static inline int cpu_mmu_index (CPUARMState *env)
 /* Bit usage when in AArch64 state */
 #define ARM_TBFLAG_AA64_EL_SHIFT    0
 #define ARM_TBFLAG_AA64_EL_MASK     (0x3 << ARM_TBFLAG_AA64_EL_SHIFT)
+#define ARM_TBFLAG_AA64_FPEN_SHIFT  2
+#define ARM_TBFLAG_AA64_FPEN_MASK   (1 << ARM_TBFLAG_AA64_FPEN_SHIFT)
 
 /* some convenience accessor macros */
 #define ARM_TBFLAG_AARCH64_STATE(F) \
@@ -1128,14 +1130,21 @@ static inline int cpu_mmu_index (CPUARMState *env)
     (((F) & ARM_TBFLAG_BSWAP_CODE_MASK) >> ARM_TBFLAG_BSWAP_CODE_SHIFT)
 #define ARM_TBFLAG_AA64_EL(F) \
     (((F) & ARM_TBFLAG_AA64_EL_MASK) >> ARM_TBFLAG_AA64_EL_SHIFT)
+#define ARM_TBFLAG_AA64_FPEN(F) \
+    (((F) & ARM_TBFLAG_AA64_FPEN_MASK) >> ARM_TBFLAG_AA64_FPEN_SHIFT)
 
 static inline void cpu_get_tb_cpu_state(CPUARMState *env, target_ulong *pc,
                                         target_ulong *cs_base, int *flags)
 {
+    int fpen = extract32(env->cp15.c1_coproc, 20, 2);
+
     if (is_a64(env)) {
         *pc = env->pc;
         *flags = ARM_TBFLAG_AARCH64_STATE_MASK
             | (arm_current_pl(env) << ARM_TBFLAG_AA64_EL_SHIFT);
+        if (fpen == 3 || (fpen == 1 && arm_current_pl(env) != 0)) {
+            *flags |= ARM_TBFLAG_AA64_FPEN_MASK;
+        }
     } else {
         int privmode;
         *pc = env->regs[15];