target/nios2: Implement Misaligned destination exception

Indirect branches, plus eret and bret optionally raise
an exception when branching to a misaligned address.
The exception is required when an mmu is enabled, but
enable it always because the fallback behaviour is not
documented (though presumably it discards low bits).

For the purposes of the linux-user cpu loop, if EXCP_UNALIGN
(misaligned data) were to arrive, it would be treated the
same as EXCP_UNALIGND (misaligned destination).  See the
!defined(CONFIG_NIOS2_ALIGNMENT_TRAP) block in kernel/traps.c.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220421151735.31996-53-richard.henderson@linaro.org>

2 files changed, 22 insertions, 2 deletions

diff --git a/target/nios2/op_helper.c b/target/nios2/op_helper.c
index a19b504..38a71a1 100644
--- a/target/nios2/op_helper.c
+++ b/target/nios2/op_helper.c
@@ -64,6 +64,13 @@ uint32_t helper_divu(CPUNios2State *env, uint32_t num, uint32_t den)
 void helper_eret(CPUNios2State *env, uint32_t new_status, uint32_t new_pc)
 {
     Nios2CPU *cpu = env_archcpu(env);
+    CPUState *cs = env_cpu(env);
+
+    if (unlikely(new_pc & 3)) {
+        env->ctrl[CR_BADADDR] = new_pc;
+        cs->exception_index = EXCP_UNALIGND;
+        cpu_loop_exit_restore(cs, GETPC());
+    }
 
     /*
      * Both estatus and bstatus have no constraints on write;
@@ -74,6 +81,6 @@ void helper_eret(CPUNios2State *env, uint32_t new_status, uint32_t new_pc)
 
     env->ctrl[CR_STATUS] = new_status;
     env->pc = new_pc;
-    cpu_loop_exit(env_cpu(env));
+    cpu_loop_exit(cs);
 }
 #endif /* !CONFIG_USER_ONLY */
diff --git a/target/nios2/translate.c b/target/nios2/translate.c
index a3e87be..794b763 100644
--- a/target/nios2/translate.c
+++ b/target/nios2/translate.c
@@ -197,11 +197,24 @@ static void gen_goto_tb(DisasContext *dc, int n, uint32_t dest)
 
 static void gen_jumpr(DisasContext *dc, int regno, bool is_call)
 {
-    tcg_gen_mov_tl(cpu_pc, load_gpr(dc, regno));
+    TCGLabel *l = gen_new_label();
+    TCGv test = tcg_temp_new();
+    TCGv dest = load_gpr(dc, regno);
+
+    tcg_gen_andi_tl(test, dest, 3);
+    tcg_gen_brcondi_tl(TCG_COND_NE, test, 0, l);
+    tcg_temp_free(test);
+
+    tcg_gen_mov_tl(cpu_pc, dest);
     if (is_call) {
         tcg_gen_movi_tl(dest_gpr(dc, R_RA), dc->base.pc_next);
     }
     tcg_gen_lookup_and_goto_ptr();
+
+    gen_set_label(l);
+    tcg_gen_st_tl(dest, cpu_env, offsetof(CPUNios2State, ctrl[CR_BADADDR]));
+    t_gen_helper_raise_exception(dc, EXCP_UNALIGND);
+
     dc->base.is_jmp = DISAS_NORETURN;
 }