github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/arch/fpu/fpu.go (about)

     1  // Copyright 2021 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package fpu provides basic floating point helpers.
    16  package fpu
    17  
    18  import (
    19  	"fmt"
    20  	"reflect"
    21  )
    22  
    23  // State represents floating point state.
    24  //
    25  // This is a simple byte slice, but may have architecture-specific methods
    26  // attached to it.
    27  type State []byte
    28  
    29  // ErrLoadingState indicates a failed restore due to unusable floating point
    30  // state.
    31  type ErrLoadingState struct {
    32  	// supported is the supported floating point state.
    33  	supportedFeatures uint64
    34  
    35  	// saved is the saved floating point state.
    36  	savedFeatures uint64
    37  }
    38  
    39  // Error returns a sensible description of the restore error.
    40  func (e ErrLoadingState) Error() string {
    41  	return fmt.Sprintf("floating point state contains unsupported features; supported: %#x saved: %#x", e.supportedFeatures, e.savedFeatures)
    42  }
    43  
    44  // alignedBytes returns a slice of size bytes, aligned in memory to the given
    45  // alignment. This is used because we require certain structures to be aligned
    46  // in a specific way (for example, the X86 floating point data).
    47  func alignedBytes(size, alignment uint) []byte {
    48  	data := make([]byte, size+alignment-1)
    49  	offset := uint(reflect.ValueOf(data).Index(0).Addr().Pointer() % uintptr(alignment))
    50  	if offset == 0 {
    51  		return data[:size:size]
    52  	}
    53  	return data[alignment-offset:][:size:size]
    54  }