Re: [PATCH v2 12/12] target/arm: Allow users to set the number of VFP registers

[Cédric Le Goater]

On 6/7/23 13:06, Joel Stanley wrote:

On Wed, 7 Jun 2023 at 04:40, Cédric Le Goater <c...@kaod.org> wrote:

Cortex A7 CPUs with an FPU implementing VFPv4 without NEON support
have 16 64-bit FPU registers and not 32 registers. Let users set the
number of VFP registers with a CPU property.

The primary use case of this property is for the Cortex A7 of the
Aspeed AST2600 SoC.

Signed-off-by: Cédric Le Goater <c...@kaod.org>

You saw a crash with a buildroot image without this change, as I recall?

yes, when compiled with VFPv4d32 support, user space crashes on real HW.

Thanks,

C.

The logic is a bit hard to follow but it is good to see a fix.

Reviewed-by: Joel Stanley <j...@jms.id.au>

---
  target/arm/cpu.h        |  2 ++
  hw/arm/aspeed_ast2600.c |  2 ++
  target/arm/cpu.c        | 32 ++++++++++++++++++++++++++++++++
  3 files changed, 36 insertions(+)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index d469a2637b32..79f1a96ddf39 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -916,6 +916,8 @@ struct ArchCPU {
      bool has_pmu;
      /* CPU has VFP */
      bool has_vfp;
+    /* CPU has 32 VFP registers */
+    bool has_vfp_d32;
      /* CPU has Neon */
      bool has_neon;
      /* CPU has M-profile DSP extension */
diff --git a/hw/arm/aspeed_ast2600.c b/hw/arm/aspeed_ast2600.c
index 1bf12461481c..a8b3a8065a11 100644
--- a/hw/arm/aspeed_ast2600.c
+++ b/hw/arm/aspeed_ast2600.c
@@ -316,6 +316,8 @@ static void aspeed_soc_ast2600_realize(DeviceState *dev, 
Error **errp)
                                  &error_abort);
          object_property_set_bool(OBJECT(&s->cpu[i]), "neon", false,
                                  &error_abort);
+        object_property_set_bool(OBJECT(&s->cpu[i]), "vfp-d32", false,
+                                &error_abort);
          object_property_set_link(OBJECT(&s->cpu[i]), "memory",
                                   OBJECT(s->memory), &error_abort);

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 5182ed0c9113..74fe6ae78192 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -1275,6 +1275,9 @@ static Property arm_cpu_cfgend_property =
  static Property arm_cpu_has_vfp_property =
              DEFINE_PROP_BOOL("vfp", ARMCPU, has_vfp, true);

+static Property arm_cpu_has_vfp_d32_property =
+            DEFINE_PROP_BOOL("vfp-d32", ARMCPU, has_vfp_d32, true);
+
  static Property arm_cpu_has_neon_property =
              DEFINE_PROP_BOOL("neon", ARMCPU, has_neon, true);

@@ -1406,6 +1409,22 @@ void arm_cpu_post_init(Object *obj)
          }
      }

+    if (cpu->has_vfp && cpu_isar_feature(aa32_simd_r32, cpu)) {
+        cpu->has_vfp_d32 = true;
+        if (!kvm_enabled()) {
+            /*
+             * The permitted values of the SIMDReg bits [3:0] on
+             * Armv8-A are either 0b0000 and 0b0010. On such CPUs,
+             * make sure that has_vfp_d32 can not be set to false.
+             */
+            if (!(arm_feature(&cpu->env, ARM_FEATURE_V8) &&
+                  !arm_feature(&cpu->env, ARM_FEATURE_M))) {
+                qdev_property_add_static(DEVICE(obj),
+                                         &arm_cpu_has_vfp_d32_property);
+            }
+        }
+    }
+
      if (arm_feature(&cpu->env, ARM_FEATURE_NEON)) {
          cpu->has_neon = true;
          if (!kvm_enabled()) {
@@ -1672,6 +1691,19 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
**errp)
          return;
      }

+    if (cpu->has_vfp_d32 != cpu->has_neon) {
+        error_setg(errp, "ARM CPUs must have both VFP-D32 and Neon or 
neither");
+        return;
+    }
+
+   if (!cpu->has_vfp_d32) {
+        uint32_t u;
+
+        u = cpu->isar.mvfr0;
+        u = FIELD_DP32(u, MVFR0, SIMDREG, 1); /* 16 registers */
+        cpu->isar.mvfr0 = u;
+    }
+
      if (!cpu->has_vfp) {
          uint64_t t;
          uint32_t u;
--
2.40.1