target/arm: fix missing exception class

The DAIF and PAC checks used raise_exception_ra to raise an exception
and unwind CPU state but raise_exception_ra is currently designed for
handling data aborts as the syndrome is partially precomputed and
encoded in the TB and then merged in merge_syn_data_abort when handling
the data abort.  Using raise_exception_ra for DAIF and PAC checks
results in an empty syndrome being retrieved from data[2] in
restore_state_to_opc and setting ESR to 0.  This manifested as:

  kvm [571]: Unknown exception class: esr: 0x000000 –
  Unknown/Uncategorized

when launching a KVM guest when the host qemu used a CPU supporting
EL2+pointer authentication and enabling pointer authentication in the
guest.

Rework raise_exception_ra such that the state is restored before raising
the exception so that the exception is not clobbered by
restore_state_to_opc.

Fixes: 0d43e1a2 ("target/arm: Add PAuth helpers")
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jamie Iles <jamie@nuviainc.com>
[PMM: added comment]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/op_helper.c

@@ -63,8 +63,15 @@ void raise_exception(CPUARMState *env, uint32_t excp,
 void raise_exception_ra(CPUARMState *env, uint32_t excp, uint32_t syndrome,
                         uint32_t target_el, uintptr_t ra)
 {
-    CPUState *cs = do_raise_exception(env, excp, syndrome, target_el);
-    cpu_loop_exit_restore(cs, ra);
+    CPUState *cs = env_cpu(env);
+
+    /*
+     * restore_state_to_opc() will set env->exception.syndrome, so
+     * we must restore CPU state here before setting the syndrome
+     * the caller passed us, and cannot use cpu_loop_exit_restore().
+     */
+    cpu_restore_state(cs, ra, true);
+    raise_exception(env, excp, syndrome, target_el);
 }
 
 uint64_t HELPER(neon_tbl)(CPUARMState *env, uint32_t desc,