From d1ff996788a41280e2e0213b9571afeca4d6ca90 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Tue, 5 Nov 2024 10:09:53 +0000 Subject: target/arm: Explicitly set 2-NaN propagation rule Set the 2-NaN propagation rule explicitly in the float_status words we use. We wrap this plus the pre-existing setting of the tininess-before-rounding flag in a new function arm_set_default_fp_behaviours() to avoid repetition, since we have a lot of float_status words at this point. The situation with FPA11 emulation in linux-user is a little odd, and arguably "correct" behaviour there would be to exactly match a real Linux kernel's FPA11 emulation. However FPA11 emulation is essentially dead at this point and so it seems better to continue with QEMU's current behaviour and leave a comment describing the situation. Signed-off-by: Peter Maydell Reviewed-by: Richard Henderson Message-id: 20241025141254.2141506-4-peter.maydell@linaro.org --- target/arm/cpu.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) (limited to 'target/arm/cpu.c') diff --git a/target/arm/cpu.c b/target/arm/cpu.c index 5b75143..6938161 100644 --- a/target/arm/cpu.c +++ b/target/arm/cpu.c @@ -168,6 +168,18 @@ void arm_register_el_change_hook(ARMCPU *cpu, ARMELChangeHookFn *hook, QLIST_INSERT_HEAD(&cpu->el_change_hooks, entry, node); } +/* + * Set the float_status behaviour to match the Arm defaults: + * * tininess-before-rounding + * * 2-input NaN propagation prefers SNaN over QNaN, and then + * operand A over operand B (see FPProcessNaNs() pseudocode) + */ +static void arm_set_default_fp_behaviours(float_status *s) +{ + set_float_detect_tininess(float_tininess_before_rounding, s); + set_float_2nan_prop_rule(float_2nan_prop_s_ab, s); +} + static void cp_reg_reset(gpointer key, gpointer value, gpointer opaque) { /* Reset a single ARMCPRegInfo register */ @@ -549,14 +561,11 @@ static void arm_cpu_reset_hold(Object *obj, ResetType type) set_flush_inputs_to_zero(1, &env->vfp.standard_fp_status); set_default_nan_mode(1, &env->vfp.standard_fp_status); set_default_nan_mode(1, &env->vfp.standard_fp_status_f16); - set_float_detect_tininess(float_tininess_before_rounding, - &env->vfp.fp_status); - set_float_detect_tininess(float_tininess_before_rounding, - &env->vfp.standard_fp_status); - set_float_detect_tininess(float_tininess_before_rounding, - &env->vfp.fp_status_f16); - set_float_detect_tininess(float_tininess_before_rounding, - &env->vfp.standard_fp_status_f16); + arm_set_default_fp_behaviours(&env->vfp.fp_status); + arm_set_default_fp_behaviours(&env->vfp.standard_fp_status); + arm_set_default_fp_behaviours(&env->vfp.fp_status_f16); + arm_set_default_fp_behaviours(&env->vfp.standard_fp_status_f16); + #ifndef CONFIG_USER_ONLY if (kvm_enabled()) { kvm_arm_reset_vcpu(cpu); -- cgit v1.1