target/nios2: Update helper_eret for shadow registers

When CRS = 0, we restore from estatus; otherwise from sstatus.
Update for the new CRS.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220421151735.31996-56-richard.henderson@linaro.org>

3 files changed, 16 insertions, 8 deletions

diff --git a/target/nios2/cpu.h b/target/nios2/cpu.h
index cca821cf80..eb171a33e6 100644
--- a/target/nios2/cpu.h
+++ b/target/nios2/cpu.h
@@ -82,6 +82,7 @@ enum {
     R_FP     = 28,
     R_EA     = 29,
     R_BA     = 30,
+    R_SSTATUS = 30,
     R_RA     = 31,
 };
 
diff --git a/target/nios2/op_helper.c b/target/nios2/op_helper.c
index a3164f5356..94040102f4 100644
--- a/target/nios2/op_helper.c
+++ b/target/nios2/op_helper.c
@@ -73,14 +73,18 @@ void helper_eret(CPUNios2State *env, uint32_t new_status, uint32_t new_pc)
     }
 
     /*
-     * Both estatus and bstatus have no constraints on write;
+     * None of estatus, bstatus, or sstatus have constraints on write;
      * do not allow reserved fields in status to be set.
-     * TODO: more than this is required for shadow registers.
+     * When shadow registers are enabled, eret *does* restore CRS.
+     * Rather than testing eic_present to decide, mask CRS out of
+     * the set of readonly fields.
      */
-    new_status &= cpu->cr_state[CR_STATUS].writable;
+    new_status &= cpu->cr_state[CR_STATUS].writable |
+                  (cpu->cr_state[CR_STATUS].readonly & R_CR_STATUS_CRS_MASK);
 
     env->ctrl[CR_STATUS] = new_status;
     env->pc = new_pc;
+    nios2_update_crs(env);
     cpu_loop_exit(cs);
 }
 
diff --git a/target/nios2/translate.c b/target/nios2/translate.c
index e566175db5..b52f98180d 100644
--- a/target/nios2/translate.c
+++ b/target/nios2/translate.c
@@ -496,11 +496,14 @@ static void eret(DisasContext *dc, uint32_t code, uint32_t flags)
 #ifdef CONFIG_USER_ONLY
     g_assert_not_reached();
 #else
-    TCGv tmp = tcg_temp_new();
-    tcg_gen_ld_tl(tmp, cpu_env, offsetof(CPUNios2State, ctrl[CR_ESTATUS]));
-    gen_helper_eret(cpu_env, tmp, load_gpr(dc, R_EA));
-    tcg_temp_free(tmp);
-
+    if (FIELD_EX32(dc->tb_flags, TBFLAGS, CRS0)) {
+        TCGv tmp = tcg_temp_new();
+        tcg_gen_ld_tl(tmp, cpu_env, offsetof(CPUNios2State, ctrl[CR_ESTATUS]));
+        gen_helper_eret(cpu_env, tmp, load_gpr(dc, R_EA));
+        tcg_temp_free(tmp);
+    } else {
+        gen_helper_eret(cpu_env, load_gpr(dc, R_SSTATUS), load_gpr(dc, R_EA));
+    }
     dc->base.is_jmp = DISAS_NORETURN;
 #endif
 }