[PULL 56/68] target/nios2: Implement Misaligned destination exception

[Richard Henderson]

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>
---
 linux-user/nios2/cpu_loop.c |  6 ++++++
 target/nios2/op_helper.c    |  9 ++++++++-
 target/nios2/translate.c    | 15 ++++++++++++++-
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/linux-user/nios2/cpu_loop.c b/linux-user/nios2/cpu_loop.c
index 11ecb71843..30a27f252b 100644
--- a/linux-user/nios2/cpu_loop.c
+++ b/linux-user/nios2/cpu_loop.c
@@ -42,6 +42,12 @@ void cpu_loop(CPUNios2State *env)
             force_sig_fault(TARGET_SIGFPE, TARGET_FPE_INTDIV, env->pc);
             break;
 
+        case EXCP_UNALIGN:
+        case EXCP_UNALIGND:
+            force_sig_fault(TARGET_SIGBUS, TARGET_BUS_ADRALN,
+                            env->ctrl[CR_BADADDR]);
+            break;
+
         case EXCP_TRAP:
             /*
              * TODO: This advance should be done in the translator, as
diff --git a/target/nios2/op_helper.c b/target/nios2/op_helper.c
index a19b504b0e..38a71a1f2d 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 a3e87beba4..794b763d8a 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;
 }
 
-- 
2.34.1