target/m68k: Map FPU exceptions to FPSR register

Add helpers for reading/writing the 68881 FPSR register so that
changes in floating point exception state can be seen by the
application.

Call these helpers in pre_load/post_load hooks to synchronize
exception state.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230803035231.429697-1-keithp@keithp.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/m68k/cpu.c

@@ -390,12 +390,19 @@ static const VMStateDescription vmstate_freg = {
     }
 };
 
+static int fpu_pre_save(void *opaque)
+{
+    M68kCPU *s = opaque;
+
+    s->env.fpsr = cpu_m68k_get_fpsr(&s->env);
+    return 0;
+}
+
 static int fpu_post_load(void *opaque, int version)
 {
     M68kCPU *s = opaque;
 
-    cpu_m68k_restore_fp_status(&s->env);
-
+    cpu_m68k_set_fpsr(&s->env, s->env.fpsr);
     return 0;
 }
 
@@ -404,6 +411,7 @@ const VMStateDescription vmmstate_fpu = {
     .version_id = 1,
     .minimum_version_id = 1,
     .needed = fpu_needed,
+    .pre_save = fpu_pre_save,
     .post_load = fpu_post_load,
     .fields = (const VMStateField[]) {
         VMSTATE_UINT32(env.fpcr, M68kCPU),

target/m68k/cpu.h

@@ -199,7 +199,8 @@ void cpu_m68k_set_ccr(CPUM68KState *env, uint32_t);
 void cpu_m68k_set_sr(CPUM68KState *env, uint32_t);
 void cpu_m68k_restore_fp_status(CPUM68KState *env);
 void cpu_m68k_set_fpcr(CPUM68KState *env, uint32_t val);
-
+uint32_t cpu_m68k_get_fpsr(CPUM68KState *env);
+void cpu_m68k_set_fpsr(CPUM68KState *env, uint32_t val);
 
 /*
  * Instead of computing the condition codes after each m68k instruction,

target/m68k/fpu_helper.c

@@ -164,6 +164,78 @@ void HELPER(set_fpcr)(CPUM68KState *env, uint32_t val)
     cpu_m68k_set_fpcr(env, val);
 }
 
+/* Convert host exception flags to cpu_m68k form.  */
+static int cpu_m68k_exceptbits_from_host(int host_bits)
+{
+    int target_bits = 0;
+
+    if (host_bits & float_flag_invalid) {
+        target_bits |= 0x80;
+    }
+    if (host_bits & float_flag_overflow) {
+        target_bits |= 0x40;
+    }
+    if (host_bits & (float_flag_underflow | float_flag_output_denormal)) {
+        target_bits |= 0x20;
+    }
+    if (host_bits & float_flag_divbyzero) {
+        target_bits |= 0x10;
+    }
+    if (host_bits & float_flag_inexact) {
+        target_bits |= 0x08;
+    }
+    return target_bits;
+}
+
+/* Convert cpu_m68k exception flags to target form.  */
+static int cpu_m68k_exceptbits_to_host(int target_bits)
+{
+    int host_bits = 0;
+
+    if (target_bits & 0x80) {
+        host_bits |= float_flag_invalid;
+    }
+    if (target_bits & 0x40) {
+        host_bits |= float_flag_overflow;
+    }
+    if (target_bits & 0x20) {
+        host_bits |= float_flag_underflow;
+    }
+    if (target_bits & 0x10) {
+        host_bits |= float_flag_divbyzero;
+    }
+    if (target_bits & 0x08) {
+        host_bits |= float_flag_inexact;
+    }
+    return host_bits;
+}
+
+uint32_t cpu_m68k_get_fpsr(CPUM68KState *env)
+{
+    int host_flags = get_float_exception_flags(&env->fp_status);
+    int target_flags = cpu_m68k_exceptbits_from_host(host_flags);
+    int except = (env->fpsr & ~(0xf8)) | target_flags;
+    return except;
+}
+
+uint32_t HELPER(get_fpsr)(CPUM68KState *env)
+{
+    return cpu_m68k_get_fpsr(env);
+}
+
+void cpu_m68k_set_fpsr(CPUM68KState *env, uint32_t val)
+{
+    env->fpsr = val;
+
+    int host_flags = cpu_m68k_exceptbits_to_host((int) env->fpsr);
+    set_float_exception_flags(host_flags, &env->fp_status);
+}
+
+void HELPER(set_fpsr)(CPUM68KState *env, uint32_t val)
+{
+    cpu_m68k_set_fpsr(env, val);
+}
+
 #define PREC_BEGIN(prec)                                        \
     do {                                                        \
         FloatX80RoundPrec old =                                 \

target/m68k/helper.c

@@ -87,7 +87,7 @@ static int m68k_fpu_gdb_get_reg(CPUState *cs, GByteArray *mem_buf, int n)
     case 8: /* fpcontrol */
         return gdb_get_reg32(mem_buf, env->fpcr);
     case 9: /* fpstatus */
-        return gdb_get_reg32(mem_buf, env->fpsr);
+        return gdb_get_reg32(mem_buf, cpu_m68k_get_fpsr(env));
     case 10: /* fpiar, not implemented */
         return gdb_get_reg32(mem_buf, 0);
     }
@@ -109,7 +109,7 @@ static int m68k_fpu_gdb_set_reg(CPUState *cs, uint8_t *mem_buf, int n)
         cpu_m68k_set_fpcr(env, ldl_p(mem_buf));
         return 4;
     case 9: /* fpstatus */
-        env->fpsr = ldl_p(mem_buf);
+        cpu_m68k_set_fpsr(env, ldl_p(mem_buf));
         return 4;
     case 10: /* fpiar, not implemented */
         return 4;

target/m68k/helper.h

@@ -54,6 +54,8 @@ DEF_HELPER_4(fsdiv, void, env, fp, fp, fp)
 DEF_HELPER_4(fddiv, void, env, fp, fp, fp)
 DEF_HELPER_4(fsgldiv, void, env, fp, fp, fp)
 DEF_HELPER_FLAGS_3(fcmp, TCG_CALL_NO_RWG, void, env, fp, fp)
+DEF_HELPER_2(set_fpsr, void, env, i32)
+DEF_HELPER_1(get_fpsr, i32, env)
 DEF_HELPER_FLAGS_2(set_fpcr, TCG_CALL_NO_RWG, void, env, i32)
 DEF_HELPER_FLAGS_2(ftst, TCG_CALL_NO_RWG, void, env, fp)
 DEF_HELPER_3(fconst, void, env, fp, i32)

target/m68k/translate.c

@@ -4686,7 +4686,7 @@ static void gen_load_fcr(DisasContext *s, TCGv res, int reg)
         tcg_gen_movi_i32(res, 0);
         break;
     case M68K_FPSR:
-        tcg_gen_ld_i32(res, tcg_env, offsetof(CPUM68KState, fpsr));
+        gen_helper_get_fpsr(res, tcg_env);
         break;
     case M68K_FPCR:
         tcg_gen_ld_i32(res, tcg_env, offsetof(CPUM68KState, fpcr));
@@ -4700,7 +4700,7 @@ static void gen_store_fcr(DisasContext *s, TCGv val, int reg)
     case M68K_FPIAR:
         break;
     case M68K_FPSR:
-        tcg_gen_st_i32(val, tcg_env, offsetof(CPUM68KState, fpsr));
+        gen_helper_set_fpsr(tcg_env, val);
         break;
     case M68K_FPCR:
         gen_helper_set_fpcr(tcg_env, val);