target/openrisc: Use cpu_unwind_state_data for mfspr

Since we do not plan to exit, use cpu_unwind_state_data
and extract exactly the data requested.

This is a bug fix, in that we no longer clobber dflag.

Consider:

        l.j       L2         // branch
        l.mfspr   r1, ppc    // delay

L1:     boom
L2:     l.lwa     r3, (r4)

Here, dflag would be set by cpu_restore_state (because that is the current
state of the cpu), but but not cleared by tb_stop on exiting the TB
(because DisasContext has recorded the current value as zero).

The next TB begins at L2 with dflag incorrectly set.  If the load has a
tlb miss, then the exception will be delivered as per a delay slot:
with DSX set in the status register and PC decremented (delay slots
restart by re-executing the branch). This will cause the return from
interrupt to go to L1, and boom!

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

diff --git a/target/openrisc/sys_helper.c b/target/openrisc/sys_helper.c
index a3508e421def4ad5a5e8801d33d9a814f4a62454..dde2fa1623e837cdefadbf298b1d2e79056c3621 100644 (file)
--- a/target/openrisc/sys_helper.c
+++ b/target/openrisc/sys_helper.c
@@ -199,6 +199,7 @@ target_ulong HELPER(mfspr)(CPUOpenRISCState *env, target_ulong rd,
                            target_ulong spr)
 {
 #ifndef CONFIG_USER_ONLY
+    uint64_t data[TARGET_INSN_START_WORDS];
     MachineState *ms = MACHINE(qdev_get_machine());
     OpenRISCCPU *cpu = env_archcpu(env);
     CPUState *cs = env_cpu(env);
@@ -232,14 +233,20 @@ target_ulong HELPER(mfspr)(CPUOpenRISCState *env, target_ulong rd,
         return env->evbar;
 
     case TO_SPR(0, 16): /* NPC (equals PC) */
-        cpu_restore_state(cs, GETPC(), false);
+        if (cpu_unwind_state_data(cs, GETPC(), data)) {
+            return data[0];
+        }
         return env->pc;
 
     case TO_SPR(0, 17): /* SR */
         return cpu_get_sr(env);
 
     case TO_SPR(0, 18): /* PPC */
-        cpu_restore_state(cs, GETPC(), false);
+        if (cpu_unwind_state_data(cs, GETPC(), data)) {
+            if (data[1] & 2) {
+                return data[0] - 4;
+            }
+        }
         return env->ppc;
 
     case TO_SPR(0, 32): /* EPCR */