diff options
Diffstat (limited to 'tools/go_marshal/marshal/marshal.go')
| -rw-r--r-- | tools/go_marshal/marshal/marshal.go | 147 |
1 files changed, 137 insertions, 10 deletions
diff --git a/tools/go_marshal/marshal/marshal.go b/tools/go_marshal/marshal/marshal.go index a313a27ed..cb2166252 100644 --- a/tools/go_marshal/marshal/marshal.go +++ b/tools/go_marshal/marshal/marshal.go @@ -20,18 +20,56 @@ // tools/go_marshal. See the go_marshal README for details. package marshal -// Marshallable represents a type that can be marshalled to and from memory. +import ( + "io" + + "gvisor.dev/gvisor/pkg/usermem" +) + +// Task provides a subset of kernel.Task, used in marshalling. We don't import +// the kernel package directly to avoid circular dependency. +type Task interface { + // CopyScratchBuffer provides a task goroutine-local scratch buffer. See + // kernel.CopyScratchBuffer. + CopyScratchBuffer(size int) []byte + + // CopyOutBytes writes the contents of b to the task's memory. See + // kernel.CopyOutBytes. + CopyOutBytes(addr usermem.Addr, b []byte) (int, error) + + // CopyInBytes reads the contents of the task's memory to b. See + // kernel.CopyInBytes. + CopyInBytes(addr usermem.Addr, b []byte) (int, error) +} + +// Marshallable represents operations on a type that can be marshalled to and +// from memory. +// +// go-marshal automatically generates implementations for this interface for +// types marked as '+marshal'. type Marshallable interface { + io.WriterTo + // SizeBytes is the size of the memory representation of a type in // marshalled form. + // + // SizeBytes must handle a nil receiver. Practically, this means SizeBytes + // cannot deference any fields on the object implementing it (but will + // likely make use of the type of these fields). SizeBytes() int - // MarshalBytes serializes a copy of a type to dst. dst must be at least - // SizeBytes() long. + // MarshalBytes serializes a copy of a type to dst. dst may be smaller than + // SizeBytes(), which results in a part of the struct being marshalled. Note + // that this may have unexpected results for non-packed types, as implicit + // padding needs to be taken into account when reasoning about how much of + // the type is serialized. MarshalBytes(dst []byte) - // UnmarshalBytes deserializes a type from src. src must be at least - // SizeBytes() long. + // UnmarshalBytes deserializes a type from src. src may be smaller than + // SizeBytes(), which results in a partially deserialized struct. Note that + // this may have unexpected results for non-packed types, as implicit + // padding needs to be taken into account when reasoning about how much of + // the type is deserialized. UnmarshalBytes(src []byte) // Packed returns true if the marshalled size of the type is the same as the @@ -39,22 +77,111 @@ type Marshallable interface { // starting at unaligned addresses (should always be true by default for ABI // structs, verified by automatically generated tests when using // go_marshal), and has no fields marked `marshal:"unaligned"`. + // + // Packed must return the same result for all possible values of the type + // implementing it. Violating this constraint implies the type doesn't have + // a static memory layout, and will lead to memory corruption. + // Go-marshal-generated code reuses the result of Packed for multiple values + // of the same type. Packed() bool // MarshalUnsafe serializes a type by bulk copying its in-memory // representation to the dst buffer. This is only safe to do when the type // has no implicit padding, see Marshallable.Packed. When Packed would // return false, MarshalUnsafe should fall back to the safer but slower - // MarshalBytes. + // MarshalBytes. dst may be smaller than SizeBytes(), see comment for + // MarshalBytes for implications. MarshalUnsafe(dst []byte) - // UnmarshalUnsafe deserializes a type directly to the underlying memory - // allocated for the object by the runtime. + // UnmarshalUnsafe deserializes a type by directly copying to the underlying + // memory allocated for the object by the runtime. // // This allows much faster unmarshalling of types which have no implicit // padding, see Marshallable.Packed. When Packed would return false, // UnmarshalUnsafe should fall back to the safer but slower unmarshal - // mechanism implemented in UnmarshalBytes (usually by calling - // UnmarshalBytes directly). + // mechanism implemented in UnmarshalBytes. src may be smaller than + // SizeBytes(), see comment for UnmarshalBytes for implications. UnmarshalUnsafe(src []byte) + + // CopyIn deserializes a Marshallable type from a task's memory. This may + // only be called from a task goroutine. This is more efficient than calling + // UnmarshalUnsafe on Marshallable.Packed types, as the type being + // marshalled does not escape. The implementation should avoid creating + // extra copies in memory by directly deserializing to the object's + // underlying memory. + // + // If the copy-in from the task memory is only partially successful, CopyIn + // should still attempt to deserialize as much data as possible. See comment + // for UnmarshalBytes. + CopyIn(task Task, addr usermem.Addr) (int, error) + + // CopyOut serializes a Marshallable type to a task's memory. This may only + // be called from a task goroutine. This is more efficient than calling + // MarshalUnsafe on Marshallable.Packed types, as the type being serialized + // does not escape. The implementation should avoid creating extra copies in + // memory by directly serializing from the object's underlying memory. + // + // The copy-out to the task memory may be partially successful, in which + // case CopyOut returns how much data was serialized. See comment for + // MarshalBytes for implications. + CopyOut(task Task, addr usermem.Addr) (int, error) + + // CopyOutN is like CopyOut, but explicitly requests a partial + // copy-out. Note that this may yield unexpected results for non-packed + // types and the caller may only want to allow this for packed types. See + // comment on MarshalBytes. + // + // The limit must be less than or equal to SizeBytes(). + CopyOutN(task Task, addr usermem.Addr, limit int) (int, error) } + +// go-marshal generates additional functions for a type based on additional +// clauses to the +marshal directive. They are documented below. +// +// Slice API +// ========= +// +// Adding a "slice" clause to the +marshal directive for structs or newtypes on +// primitives like this: +// +// // +marshal slice:FooSlice +// type Foo struct { ... } +// +// Generates four additional functions for marshalling slices of Foos like this: +// +// // MarshalUnsafeFooSlice is like Foo.MarshalUnsafe, buf for a []Foo. It's +// // more efficient that repeatedly calling calling Foo.MarshalUnsafe over a +// // []Foo in a loop. +// func MarshalUnsafeFooSlice(src []Foo, dst []byte) (int, error) { ... } +// +// // UnmarshalUnsafeFooSlice is like Foo.UnmarshalUnsafe, buf for a []Foo. It's +// // more efficient that repeatedly calling calling Foo.UnmarshalUnsafe over a +// // []Foo in a loop. +// func UnmarshalUnsafeFooSlice(dst []Foo, src []byte) (int, error) { ... } +// +// // CopyFooSliceIn copies in a slice of Foo objects from the task's memory. +// func CopyFooSliceIn(task marshal.Task, addr usermem.Addr, dst []Foo) (int, error) { ... } +// +// // CopyFooSliceIn copies out a slice of Foo objects to the task's memory. +// func CopyFooSliceOut(task marshal.Task, addr usermem.Addr, src []Foo) (int, error) { ... } +// +// The name of the functions are of the format "Copy%sIn" and "Copy%sOut", where +// %s is the first argument to the slice clause. This directive is not supported +// for newtypes on arrays. +// +// The slice clause also takes an optional second argument, which must be the +// value "inner": +// +// // +marshal slice:Int32Slice:inner +// type Int32 int32 +// +// This is only valid on newtypes on primitives, and causes the generated +// functions to accept slices of the inner type instead: +// +// func CopyInt32SliceIn(task marshal.Task, addr usermem.Addr, dst []int32) (int, error) { ... } +// +// Without "inner", they would instead be: +// +// func CopyInt32SliceIn(task marshal.Task, addr usermem.Addr, dst []Int32) (int, error) { ... } +// +// This may help avoid a cast depending on how the generated functions are used. |