target/openrisc: Allow fpcsr access in user mode

As per OpenRISC spec 1.4 FPCSR can be read and written in user mode.

Update mtspr and mfspr helpers to support this by moving the is_user
check into the helper.

Link: https://raw.githubusercontent.com/openrisc/doc/master/openrisc-arch-1.4-rev0.pdf
Signed-off-by: Stafford Horne <shorne@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

target/openrisc/sys_helper.c

@@ -29,17 +29,37 @@
 
 #define TO_SPR(group, number) (((group) << 11) + (number))
 
+static inline bool is_user(CPUOpenRISCState *env)
+{
+#ifdef CONFIG_USER_ONLY
+    return true;
+#else
+    return (env->sr & SR_SM) == 0;
+#endif
+}
+
 void HELPER(mtspr)(CPUOpenRISCState *env, target_ulong spr, target_ulong rb)
 {
-#ifndef CONFIG_USER_ONLY
     OpenRISCCPU *cpu = env_archcpu(env);
+#ifndef CONFIG_USER_ONLY
     CPUState *cs = env_cpu(env);
     target_ulong mr;
     int idx;
 #endif
 
+    /* Handle user accessible SPRs first.  */
     switch (spr) {
+    case TO_SPR(0, 20): /* FPCSR */
+        cpu_set_fpcsr(env, rb);
+        return;
+    }
+
+    if (is_user(env)) {
+        raise_exception(cpu, EXCP_ILLEGAL);
+    }
+
 #ifndef CONFIG_USER_ONLY
+    switch (spr) {
     case TO_SPR(0, 11): /* EVBAR */
         env->evbar = rb;
         break;
@@ -187,27 +207,33 @@ void HELPER(mtspr)(CPUOpenRISCState *env, target_ulong spr, target_ulong rb)
         cpu_openrisc_timer_update(cpu);
         qemu_mutex_unlock_iothread();
         break;
-#endif
-
-    case TO_SPR(0, 20): /* FPCSR */
-        cpu_set_fpcsr(env, rb);
-        break;
     }
+#endif
 }
 
 target_ulong HELPER(mfspr)(CPUOpenRISCState *env, target_ulong rd,
                            target_ulong spr)
 {
+    OpenRISCCPU *cpu = env_archcpu(env);
 #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);
     int idx;
 #endif
 
+    /* Handle user accessible SPRs first.  */
     switch (spr) {
+    case TO_SPR(0, 20): /* FPCSR */
+        return env->fpcsr;
+    }
+
+    if (is_user(env)) {
+        raise_exception(cpu, EXCP_ILLEGAL);
+    }
+
 #ifndef CONFIG_USER_ONLY
+    switch (spr) {
     case TO_SPR(0, 0): /* VR */
         return env->vr;
 
@@ -324,11 +350,8 @@ target_ulong HELPER(mfspr)(CPUOpenRISCState *env, target_ulong rd,
         cpu_openrisc_count_update(cpu);
         qemu_mutex_unlock_iothread();
         return cpu_openrisc_count_get(cpu);
-#endif
-
-    case TO_SPR(0, 20): /* FPCSR */
-        return env->fpcsr;
     }
+#endif
 
     /* for rd is passed in, if rd unchanged, just keep it back.  */
     return rd;

target/openrisc/translate.c

@@ -819,13 +819,10 @@ static bool trans_l_xori(DisasContext *dc, arg_rri *a)
 
 static bool trans_l_mfspr(DisasContext *dc, arg_l_mfspr *a)
 {
-    check_r0_write(dc, a->d);
-
-    if (is_user(dc)) {
-        gen_illegal_exception(dc);
-    } else {
     TCGv spr = tcg_temp_new();
 
+    check_r0_write(dc, a->d);
+
     if (tb_cflags(dc->base.tb) & CF_USE_ICOUNT) {
         gen_io_start();
         if (dc->delayed_branch) {
@@ -839,21 +836,18 @@ static bool trans_l_mfspr(DisasContext *dc, arg_l_mfspr *a)
 
     tcg_gen_ori_tl(spr, cpu_R(dc, a->a), a->k);
     gen_helper_mfspr(cpu_R(dc, a->d), cpu_env, cpu_R(dc, a->d), spr);
-    }
     return true;
 }
 
 static bool trans_l_mtspr(DisasContext *dc, arg_l_mtspr *a)
 {
-    if (is_user(dc)) {
+    TCGv spr = tcg_temp_new();
-        gen_illegal_exception(dc);
-    } else {
-        TCGv spr;
 
     if (tb_cflags(dc->base.tb) & CF_USE_ICOUNT) {
         gen_io_start();
     }
-        /* For SR, we will need to exit the TB to recognize the new
+    /*
+     * For SR, we will need to exit the TB to recognize the new
      * exception state.  For NPC, in theory this counts as a branch
      * (although the SPR only exists for use by an ICE).  Save all
      * of the cpu state first, allowing it to be overwritten.
@@ -866,10 +860,8 @@ static bool trans_l_mtspr(DisasContext *dc, arg_l_mtspr *a)
     }
     dc->base.is_jmp = DISAS_EXIT;
 
-        spr = tcg_temp_new();
     tcg_gen_ori_tl(spr, cpu_R(dc, a->a), a->k);
     gen_helper_mtspr(cpu_env, spr, cpu_R(dc, a->b));
-    }
     return true;
 }