[Qemu-arm] [PATCH 06/11] target-arm: Add comment about not implementing NSACR.RFR

[Peter Maydell]

QEMU doesn't implement the NSACR.RFR bit, which is a permitted
IMPDEF in choice in ARMv7 and the only permitted choice in ARMv8.
Add a comment to bad_mode_switch() to note that this is why
FIQ is always a valid mode regardless of the CPU's Secure state.

Signed-off-by: Peter Maydell <address@hidden>
---
 target-arm/helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/target-arm/helper.c b/target-arm/helper.c
index 9998a25..37b5439 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -5180,6 +5180,9 @@ static int bad_mode_switch(CPUARMState *env, int mode)
     case ARM_CPU_MODE_UND:
     case ARM_CPU_MODE_IRQ:
     case ARM_CPU_MODE_FIQ:
+        /* Note that we don't implement the IMPDEF NSACR.RFR which in v7
+         * allows FIQ mode to be Secure-only. (In v8 this doesn't exist.)
+         */
         return 0;
     case ARM_CPU_MODE_MON:
         return !arm_is_secure(env);
-- 
1.9.1