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target/alpha: Explicitly set 2-NaN propagation rule

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Set the NaN propagation rule explicitly for the float_status word
used in this target.

This is a no-behaviour-change commit, so we retain the existing
behaviour of x87-style pick-largest-significand NaN propagation.
This is however not the architecturally correct handling, so we leave
a TODO note to that effect.

We also leave a TODO note pointing out that all this code in the cpu
initfn (including the existing setting up of env->flags and the FPCR)
should be in a currently non-existent CPU reset function.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241025141254.2141506-17-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2024-11-05 10:09:56 +00:00
parent 62d39b28ef
commit 8403a5015c
2 changed files with 12 additions and 1 deletions
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2
fpu/softfloat-specialize.c.inc
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@ -406,7 +406,7 @@ static int pickNaN(FloatClass a_cls, FloatClass b_cls,
|| defined(TARGET_LOONGARCH64) || defined(TARGET_HPPA) \
|| defined(TARGET_S390X) || defined(TARGET_PPC) || defined(TARGET_M68K) \
|| defined(TARGET_SPARC) || defined(TARGET_XTENSA) \
|| defined(TARGET_I386)
|| defined(TARGET_I386) || defined(TARGET_ALPHA)
g_assert_not_reached();
#else
rule = float_2nan_prop_x87;

11
target/alpha/cpu.c
View File

@ -24,6 +24,7 @@
#include "qemu/qemu-print.h"
#include "cpu.h"
#include "exec/exec-all.h"
#include "fpu/softfloat.h"
static void alpha_cpu_set_pc(CPUState *cs, vaddr value)
@ -187,7 +188,17 @@ static void alpha_cpu_initfn(Object *obj)
{
CPUAlphaState *env = cpu_env(CPU(obj));
/* TODO all this should be done in reset, not init */
env->lock_addr = -1;
/*
* TODO: this is incorrect. The Alpha Architecture Handbook version 4
* describes NaN propagation in section 4.7.10.4. We should prefer
* the operand in Fb (whether it is a QNaN or an SNaN), then the
* operand in Fa. That is float_2nan_prop_ba.
*/
set_float_2nan_prop_rule(float_2nan_prop_x87, &env->fp_status);
#if defined(CONFIG_USER_ONLY)
env->flags = ENV_FLAG_PS_USER | ENV_FLAG_FEN;
cpu_alpha_store_fpcr(env, (uint64_t)(FPCR_INVD | FPCR_DZED | FPCR_OVFD