Move the code that manages floating-point state to a separate package

This change is inspired by Adin's cl/355256448.

PiperOrigin-RevId: 364695931

1 files changed, 54 insertions, 0 deletions

diff --git a/pkg/sentry/arch/fpu/fpu.go b/pkg/sentry/arch/fpu/fpu.go
new file mode 100644
index 000000000..867d309a3
--- /dev/null
+++ b/pkg/sentry/arch/fpu/fpu.go
@@ -0,0 +1,54 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package fpu provides basic floating point helpers.
+package fpu
+
+import (
+	"fmt"
+	"reflect"
+)
+
+// State represents floating point state.
+//
+// This is a simple byte slice, but may have architecture-specific methods
+// attached to it.
+type State []byte
+
+// ErrLoadingState indicates a failed restore due to unusable floating point
+// state.
+type ErrLoadingState struct {
+	// supported is the supported floating point state.
+	supportedFeatures uint64
+
+	// saved is the saved floating point state.
+	savedFeatures uint64
+}
+
+// Error returns a sensible description of the restore error.
+func (e ErrLoadingState) Error() string {
+	return fmt.Sprintf("floating point state contains unsupported features; supported: %#x saved: %#x", e.supportedFeatures, e.savedFeatures)
+}
+
+// alignedBytes returns a slice of size bytes, aligned in memory to the given
+// alignment. This is used because we require certain structures to be aligned
+// in a specific way (for example, the X86 floating point data).
+func alignedBytes(size, alignment uint) []byte {
+	data := make([]byte, size+alignment-1)
+	offset := uint(reflect.ValueOf(data).Index(0).Addr().Pointer() % uintptr(alignment))
+	if offset == 0 {
+		return data[:size:size]
+	}
+	return data[alignment-offset:][:size:size]
+}