target/nios2: Support division error exception

Division may (optionally) raise a division exception.
Since the linux kernel has been prepared for this for
some time, enable it by default.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220421151735.31996-42-richard.henderson@linaro.org>

6 files changed, 58 insertions, 40 deletions

diff --git a/target/nios2/cpu.c b/target/nios2/cpu.c
index 58e6ad0462..54e7071907 100644
--- a/target/nios2/cpu.c
+++ b/target/nios2/cpu.c
@@ -263,6 +263,7 @@ static int nios2_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
 }
 
 static Property nios2_properties[] = {
+    DEFINE_PROP_BOOL("diverr_present", Nios2CPU, diverr_present, true),
     DEFINE_PROP_BOOL("mmu_present", Nios2CPU, mmu_present, true),
     /* ALTR,pid-num-bits */
     DEFINE_PROP_UINT32("mmu_pid_num_bits", Nios2CPU, pid_num_bits, 8),
diff --git a/target/nios2/cpu.h b/target/nios2/cpu.h
index 08284d7927..4d63006ffe 100644
--- a/target/nios2/cpu.h
+++ b/target/nios2/cpu.h
@@ -207,7 +207,9 @@ struct ArchCPU {
     CPUNegativeOffsetState neg;
     CPUNios2State env;
 
+    bool diverr_present;
     bool mmu_present;
+
     uint32_t pid_num_bits;
     uint32_t tlb_num_ways;
     uint32_t tlb_num_entries;
diff --git a/target/nios2/helper.c b/target/nios2/helper.c
index 4d9085f22f..c5a2dd65b1 100644
--- a/target/nios2/helper.c
+++ b/target/nios2/helper.c
@@ -119,6 +119,9 @@ void nios2_cpu_do_interrupt(CPUState *cs)
         case EXCP_UNALIGND:
             name = "Misaligned (destination)";
             break;
+        case EXCP_DIV:
+            name = "DIV error";
+            break;
         case EXCP_TRAP:
             name = "TRAP insn";
             break;
@@ -187,6 +190,7 @@ void nios2_cpu_do_interrupt(CPUState *cs)
 
     case EXCP_SUPERI:
     case EXCP_ILLEGAL:
+    case EXCP_DIV:
     case EXCP_TRAP:
         do_exception(cpu, cpu->exception_addr, 0, false);
         break;
diff --git a/target/nios2/helper.h b/target/nios2/helper.h
index 525b6b685b..6f5ec60b0d 100644
--- a/target/nios2/helper.h
+++ b/target/nios2/helper.h
@@ -19,6 +19,8 @@
  */
 
 DEF_HELPER_FLAGS_2(raise_exception, TCG_CALL_NO_WG, noreturn, env, i32)
+DEF_HELPER_FLAGS_3(divs, TCG_CALL_NO_WG, s32, env, s32, s32)
+DEF_HELPER_FLAGS_3(divu, TCG_CALL_NO_WG, i32, env, i32, i32)
 
 #if !defined(CONFIG_USER_ONLY)
 DEF_HELPER_3(eret, noreturn, env, i32, i32)
diff --git a/target/nios2/op_helper.c b/target/nios2/op_helper.c
index 49fccf2c2c..a19b504b0e 100644
--- a/target/nios2/op_helper.c
+++ b/target/nios2/op_helper.c
@@ -31,6 +31,35 @@ void helper_raise_exception(CPUNios2State *env, uint32_t index)
     cpu_loop_exit(cs);
 }
 
+static void maybe_raise_div(CPUNios2State *env, uintptr_t ra)
+{
+    Nios2CPU *cpu = env_archcpu(env);
+    CPUState *cs = env_cpu(env);
+
+    if (cpu->diverr_present) {
+        cs->exception_index = EXCP_DIV;
+        cpu_loop_exit_restore(cs, ra);
+    }
+}
+
+int32_t helper_divs(CPUNios2State *env, int32_t num, int32_t den)
+{
+    if (unlikely(den == 0) || unlikely(den == -1 && num == INT32_MIN)) {
+        maybe_raise_div(env, GETPC());
+        return num; /* undefined */
+    }
+    return num / den;
+}
+
+uint32_t helper_divu(CPUNios2State *env, uint32_t num, uint32_t den)
+{
+    if (unlikely(den == 0)) {
+        maybe_raise_div(env, GETPC());
+        return num; /* undefined */
+    }
+    return num / den;
+}
+
 #ifndef CONFIG_USER_ONLY
 void helper_eret(CPUNios2State *env, uint32_t new_status, uint32_t new_pc)
 {
diff --git a/target/nios2/translate.c b/target/nios2/translate.c
index b8d75207a4..b27269bf08 100644
--- a/target/nios2/translate.c
+++ b/target/nios2/translate.c
@@ -654,59 +654,39 @@ gen_r_shift_s(ror, rotr_tl)
 static void divs(DisasContext *dc, uint32_t code, uint32_t flags)
 {
     R_TYPE(instr, (code));
+    TCGv dest;
 
-    /* Stores into R_ZERO are ignored */
-    if (unlikely(instr.c == R_ZERO)) {
-        return;
+    if (instr.c == R_ZERO) {
+        dest = tcg_temp_new();
+    } else {
+        dest = cpu_R[instr.c];
     }
 
-    TCGv t0 = tcg_temp_new();
-    TCGv t1 = tcg_temp_new();
-    TCGv t2 = tcg_temp_new();
-    TCGv t3 = tcg_temp_new();
+    gen_helper_divs(dest, cpu_env,
+                    load_gpr(dc, instr.a), load_gpr(dc, instr.b));
 
-    tcg_gen_ext32s_tl(t0, load_gpr(dc, instr.a));
-    tcg_gen_ext32s_tl(t1, load_gpr(dc, instr.b));
-    tcg_gen_setcondi_tl(TCG_COND_EQ, t2, t0, INT_MIN);
-    tcg_gen_setcondi_tl(TCG_COND_EQ, t3, t1, -1);
-    tcg_gen_and_tl(t2, t2, t3);
-    tcg_gen_setcondi_tl(TCG_COND_EQ, t3, t1, 0);
-    tcg_gen_or_tl(t2, t2, t3);
-    tcg_gen_movi_tl(t3, 0);
-    tcg_gen_movcond_tl(TCG_COND_NE, t1, t2, t3, t2, t1);
-    tcg_gen_div_tl(cpu_R[instr.c], t0, t1);
-    tcg_gen_ext32s_tl(cpu_R[instr.c], cpu_R[instr.c]);
-
-    tcg_temp_free(t3);
-    tcg_temp_free(t2);
-    tcg_temp_free(t1);
-    tcg_temp_free(t0);
+    if (instr.c == R_ZERO) {
+        tcg_temp_free(dest);
+    }
 }
 
 static void divu(DisasContext *dc, uint32_t code, uint32_t flags)
 {
     R_TYPE(instr, (code));
+    TCGv dest;
 
-    /* Stores into R_ZERO are ignored */
-    if (unlikely(instr.c == R_ZERO)) {
-        return;
+    if (instr.c == R_ZERO) {
+        dest = tcg_temp_new();
+    } else {
+        dest = cpu_R[instr.c];
     }
 
-    TCGv t0 = tcg_temp_new();
-    TCGv t1 = tcg_temp_new();
-    TCGv t2 = tcg_const_tl(0);
-    TCGv t3 = tcg_const_tl(1);
+    gen_helper_divu(dest, cpu_env,
+                    load_gpr(dc, instr.a), load_gpr(dc, instr.b));
 
-    tcg_gen_ext32u_tl(t0, load_gpr(dc, instr.a));
-    tcg_gen_ext32u_tl(t1, load_gpr(dc, instr.b));
-    tcg_gen_movcond_tl(TCG_COND_EQ, t1, t1, t2, t3, t1);
-    tcg_gen_divu_tl(cpu_R[instr.c], t0, t1);
-    tcg_gen_ext32s_tl(cpu_R[instr.c], cpu_R[instr.c]);
-
-    tcg_temp_free(t3);
-    tcg_temp_free(t2);
-    tcg_temp_free(t1);
-    tcg_temp_free(t0);
+    if (instr.c == R_ZERO) {
+        tcg_temp_free(dest);
+    }
 }
 
 static void trap(DisasContext *dc, uint32_t code, uint32_t flags)