target/i386: force maximum rounding precision for fildl[l]

The instruction description says "It is loaded without rounding
errors." which implies we should have the widest rounding mode
possible.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/888
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220315121251.2280317-4-alex.bennee@linaro.org>

diff --git a/target/i386/tcg/fpu_helper.c b/target/i386/tcg/fpu_helper.c
index cdd8e9f..ebf5e73 100644 (file)
--- a/target/i386/tcg/fpu_helper.c
+++ b/target/i386/tcg/fpu_helper.c
@@ -237,24 +237,37 @@ void helper_fldl_ST0(CPUX86State *env, uint64_t val)
     merge_exception_flags(env, old_flags);
 }
 
+static FloatX80RoundPrec tmp_maximise_precision(float_status *st)
+{
+    FloatX80RoundPrec old = get_floatx80_rounding_precision(st);
+    set_floatx80_rounding_precision(floatx80_precision_x, st);
+    return old;
+}
+
 void helper_fildl_ST0(CPUX86State *env, int32_t val)
 {
     int new_fpstt;
+    FloatX80RoundPrec old = tmp_maximise_precision(&env->fp_status);
 
     new_fpstt = (env->fpstt - 1) & 7;
     env->fpregs[new_fpstt].d = int32_to_floatx80(val, &env->fp_status);
     env->fpstt = new_fpstt;
     env->fptags[new_fpstt] = 0; /* validate stack entry */
+
+    set_floatx80_rounding_precision(old, &env->fp_status);
 }
 
 void helper_fildll_ST0(CPUX86State *env, int64_t val)
 {
     int new_fpstt;
+    FloatX80RoundPrec old = tmp_maximise_precision(&env->fp_status);
 
     new_fpstt = (env->fpstt - 1) & 7;
     env->fpregs[new_fpstt].d = int64_to_floatx80(val, &env->fp_status);
     env->fpstt = new_fpstt;
     env->fptags[new_fpstt] = 0; /* validate stack entry */
+
+    set_floatx80_rounding_precision(old, &env->fp_status);
 }
 
 uint32_t helper_fsts_ST0(CPUX86State *env)