465 lines
15 KiB
Go
465 lines
15 KiB
Go
package wasm
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import (
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"container/list"
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"encoding/binary"
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"fmt"
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"math"
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"reflect"
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"sync"
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"sync/atomic"
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"time"
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"unsafe"
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"github.com/tetratelabs/wazero/api"
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"github.com/tetratelabs/wazero/experimental"
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"github.com/tetratelabs/wazero/internal/internalapi"
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"github.com/tetratelabs/wazero/internal/wasmruntime"
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)
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const (
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// MemoryPageSize is the unit of memory length in WebAssembly,
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// and is defined as 2^16 = 65536.
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// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#memory-instances%E2%91%A0
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MemoryPageSize = uint32(65536)
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// MemoryLimitPages is maximum number of pages defined (2^16).
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// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#grow-mem
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MemoryLimitPages = uint32(65536)
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// MemoryPageSizeInBits satisfies the relation: "1 << MemoryPageSizeInBits == MemoryPageSize".
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MemoryPageSizeInBits = 16
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)
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// compile-time check to ensure MemoryInstance implements api.Memory
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var _ api.Memory = &MemoryInstance{}
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type waiters struct {
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mux sync.Mutex
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l *list.List
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}
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// MemoryInstance represents a memory instance in a store, and implements api.Memory.
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//
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// Note: In WebAssembly 1.0 (20191205), there may be up to one Memory per store, which means the precise memory is always
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// wasm.Store Memories index zero: `store.Memories[0]`
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// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#memory-instances%E2%91%A0.
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type MemoryInstance struct {
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internalapi.WazeroOnlyType
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Buffer []byte
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Min, Cap, Max uint32
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Shared bool
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// definition is known at compile time.
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definition api.MemoryDefinition
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// Mux is used in interpreter mode to prevent overlapping calls to atomic instructions,
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// introduced with WebAssembly threads proposal.
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Mux sync.Mutex
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// waiters implements atomic wait and notify. It is implemented similarly to golang.org/x/sync/semaphore,
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// with a fixed weight of 1 and no spurious notifications.
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waiters sync.Map
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// ownerModuleEngine is the module engine that owns this memory instance.
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ownerModuleEngine ModuleEngine
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expBuffer experimental.LinearMemory
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}
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// NewMemoryInstance creates a new instance based on the parameters in the SectionIDMemory.
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func NewMemoryInstance(memSec *Memory, allocator experimental.MemoryAllocator, moduleEngine ModuleEngine) *MemoryInstance {
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minBytes := MemoryPagesToBytesNum(memSec.Min)
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capBytes := MemoryPagesToBytesNum(memSec.Cap)
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maxBytes := MemoryPagesToBytesNum(memSec.Max)
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var buffer []byte
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var expBuffer experimental.LinearMemory
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if allocator != nil {
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expBuffer = allocator.Allocate(capBytes, maxBytes)
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buffer = expBuffer.Reallocate(minBytes)
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} else if memSec.IsShared {
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// Shared memory needs a fixed buffer, so allocate with the maximum size.
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//
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// The rationale as to why we can simply use make([]byte) to a fixed buffer is that Go's GC is non-relocating.
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// That is not a part of Go spec, but is well-known thing in Go community (wazero's compiler heavily relies on it!)
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// * https://github.com/go4org/unsafe-assume-no-moving-gc
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//
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// Also, allocating Max here isn't harmful as the Go runtime uses mmap for large allocations, therefore,
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// the memory buffer allocation here is virtual and doesn't consume physical memory until it's used.
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// * https://github.com/golang/go/blob/8121604559035734c9677d5281bbdac8b1c17a1e/src/runtime/malloc.go#L1059
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// * https://github.com/golang/go/blob/8121604559035734c9677d5281bbdac8b1c17a1e/src/runtime/malloc.go#L1165
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buffer = make([]byte, minBytes, maxBytes)
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} else {
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buffer = make([]byte, minBytes, capBytes)
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}
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return &MemoryInstance{
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Buffer: buffer,
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Min: memSec.Min,
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Cap: memoryBytesNumToPages(uint64(cap(buffer))),
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Max: memSec.Max,
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Shared: memSec.IsShared,
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expBuffer: expBuffer,
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ownerModuleEngine: moduleEngine,
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}
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}
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// Definition implements the same method as documented on api.Memory.
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func (m *MemoryInstance) Definition() api.MemoryDefinition {
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return m.definition
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}
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// Size implements the same method as documented on api.Memory.
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func (m *MemoryInstance) Size() uint32 {
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return uint32(len(m.Buffer))
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}
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// ReadByte implements the same method as documented on api.Memory.
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func (m *MemoryInstance) ReadByte(offset uint32) (byte, bool) {
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if !m.hasSize(offset, 1) {
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return 0, false
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}
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return m.Buffer[offset], true
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}
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// ReadUint16Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) ReadUint16Le(offset uint32) (uint16, bool) {
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if !m.hasSize(offset, 2) {
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return 0, false
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}
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return binary.LittleEndian.Uint16(m.Buffer[offset : offset+2]), true
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}
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// ReadUint32Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) ReadUint32Le(offset uint32) (uint32, bool) {
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return m.readUint32Le(offset)
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}
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// ReadFloat32Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) ReadFloat32Le(offset uint32) (float32, bool) {
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v, ok := m.readUint32Le(offset)
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if !ok {
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return 0, false
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}
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return math.Float32frombits(v), true
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}
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// ReadUint64Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) ReadUint64Le(offset uint32) (uint64, bool) {
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return m.readUint64Le(offset)
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}
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// ReadFloat64Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) ReadFloat64Le(offset uint32) (float64, bool) {
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v, ok := m.readUint64Le(offset)
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if !ok {
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return 0, false
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}
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return math.Float64frombits(v), true
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}
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// Read implements the same method as documented on api.Memory.
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func (m *MemoryInstance) Read(offset, byteCount uint32) ([]byte, bool) {
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if !m.hasSize(offset, uint64(byteCount)) {
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return nil, false
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}
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return m.Buffer[offset : offset+byteCount : offset+byteCount], true
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}
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// WriteByte implements the same method as documented on api.Memory.
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func (m *MemoryInstance) WriteByte(offset uint32, v byte) bool {
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if !m.hasSize(offset, 1) {
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return false
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}
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m.Buffer[offset] = v
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return true
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}
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// WriteUint16Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) WriteUint16Le(offset uint32, v uint16) bool {
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if !m.hasSize(offset, 2) {
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return false
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}
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binary.LittleEndian.PutUint16(m.Buffer[offset:], v)
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return true
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}
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// WriteUint32Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) WriteUint32Le(offset, v uint32) bool {
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return m.writeUint32Le(offset, v)
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}
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// WriteFloat32Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) WriteFloat32Le(offset uint32, v float32) bool {
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return m.writeUint32Le(offset, math.Float32bits(v))
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}
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// WriteUint64Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) WriteUint64Le(offset uint32, v uint64) bool {
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return m.writeUint64Le(offset, v)
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}
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// WriteFloat64Le implements the same method as documented on api.Memory.
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func (m *MemoryInstance) WriteFloat64Le(offset uint32, v float64) bool {
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return m.writeUint64Le(offset, math.Float64bits(v))
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}
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// Write implements the same method as documented on api.Memory.
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func (m *MemoryInstance) Write(offset uint32, val []byte) bool {
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if !m.hasSize(offset, uint64(len(val))) {
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return false
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}
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copy(m.Buffer[offset:], val)
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return true
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}
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// WriteString implements the same method as documented on api.Memory.
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func (m *MemoryInstance) WriteString(offset uint32, val string) bool {
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if !m.hasSize(offset, uint64(len(val))) {
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return false
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}
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copy(m.Buffer[offset:], val)
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return true
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}
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// MemoryPagesToBytesNum converts the given pages into the number of bytes contained in these pages.
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func MemoryPagesToBytesNum(pages uint32) (bytesNum uint64) {
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return uint64(pages) << MemoryPageSizeInBits
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}
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// Grow implements the same method as documented on api.Memory.
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func (m *MemoryInstance) Grow(delta uint32) (result uint32, ok bool) {
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currentPages := m.Pages()
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if delta == 0 {
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return currentPages, true
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}
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// If exceeds the max of memory size, we push -1 according to the spec.
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newPages := currentPages + delta
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if newPages > m.Max || int32(delta) < 0 {
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return 0, false
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} else if m.expBuffer != nil {
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buffer := m.expBuffer.Reallocate(MemoryPagesToBytesNum(newPages))
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if m.Shared {
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if unsafe.SliceData(buffer) != unsafe.SliceData(m.Buffer) {
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panic("shared memory cannot move, this is a bug in the memory allocator")
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}
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// We assume grow is called under a guest lock.
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// But the memory length is accessed elsewhere,
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// so use atomic to make the new length visible across threads.
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atomicStoreLengthAndCap(&m.Buffer, uintptr(len(buffer)), uintptr(cap(buffer)))
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m.Cap = memoryBytesNumToPages(uint64(cap(buffer)))
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} else {
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m.Buffer = buffer
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m.Cap = newPages
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}
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} else if newPages > m.Cap { // grow the memory.
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if m.Shared {
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panic("shared memory cannot be grown, this is a bug in wazero")
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}
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m.Buffer = append(m.Buffer, make([]byte, MemoryPagesToBytesNum(delta))...)
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m.Cap = newPages
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} else { // We already have the capacity we need.
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if m.Shared {
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// We assume grow is called under a guest lock.
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// But the memory length is accessed elsewhere,
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// so use atomic to make the new length visible across threads.
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atomicStoreLength(&m.Buffer, uintptr(MemoryPagesToBytesNum(newPages)))
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} else {
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m.Buffer = m.Buffer[:MemoryPagesToBytesNum(newPages)]
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}
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}
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m.ownerModuleEngine.MemoryGrown()
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return currentPages, true
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}
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// Pages implements the same method as documented on api.Memory.
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func (m *MemoryInstance) Pages() (result uint32) {
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return memoryBytesNumToPages(uint64(len(m.Buffer)))
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}
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// PagesToUnitOfBytes converts the pages to a human-readable form similar to what's specified. e.g. 1 -> "64Ki"
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//
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// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#memory-instances%E2%91%A0
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func PagesToUnitOfBytes(pages uint32) string {
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k := pages * 64
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if k < 1024 {
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return fmt.Sprintf("%d Ki", k)
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}
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m := k / 1024
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if m < 1024 {
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return fmt.Sprintf("%d Mi", m)
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}
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g := m / 1024
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if g < 1024 {
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return fmt.Sprintf("%d Gi", g)
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}
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return fmt.Sprintf("%d Ti", g/1024)
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}
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// Below are raw functions used to implement the api.Memory API:
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// Uses atomic write to update the length of a slice.
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func atomicStoreLengthAndCap(slice *[]byte, length uintptr, cap uintptr) {
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slicePtr := (*reflect.SliceHeader)(unsafe.Pointer(slice))
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capPtr := (*uintptr)(unsafe.Pointer(&slicePtr.Cap))
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atomic.StoreUintptr(capPtr, cap)
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lenPtr := (*uintptr)(unsafe.Pointer(&slicePtr.Len))
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atomic.StoreUintptr(lenPtr, length)
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}
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// Uses atomic write to update the length of a slice.
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func atomicStoreLength(slice *[]byte, length uintptr) {
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slicePtr := (*reflect.SliceHeader)(unsafe.Pointer(slice))
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lenPtr := (*uintptr)(unsafe.Pointer(&slicePtr.Len))
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atomic.StoreUintptr(lenPtr, length)
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}
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// memoryBytesNumToPages converts the given number of bytes into the number of pages.
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func memoryBytesNumToPages(bytesNum uint64) (pages uint32) {
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return uint32(bytesNum >> MemoryPageSizeInBits)
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}
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// hasSize returns true if Len is sufficient for byteCount at the given offset.
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//
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// Note: This is always fine, because memory can grow, but never shrink.
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func (m *MemoryInstance) hasSize(offset uint32, byteCount uint64) bool {
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return uint64(offset)+byteCount <= uint64(len(m.Buffer)) // uint64 prevents overflow on add
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}
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// readUint32Le implements ReadUint32Le without using a context. This is extracted as both ints and floats are stored in
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// memory as uint32le.
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func (m *MemoryInstance) readUint32Le(offset uint32) (uint32, bool) {
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if !m.hasSize(offset, 4) {
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return 0, false
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}
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return binary.LittleEndian.Uint32(m.Buffer[offset : offset+4]), true
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}
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// readUint64Le implements ReadUint64Le without using a context. This is extracted as both ints and floats are stored in
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// memory as uint64le.
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func (m *MemoryInstance) readUint64Le(offset uint32) (uint64, bool) {
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if !m.hasSize(offset, 8) {
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return 0, false
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}
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return binary.LittleEndian.Uint64(m.Buffer[offset : offset+8]), true
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}
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// writeUint32Le implements WriteUint32Le without using a context. This is extracted as both ints and floats are stored
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// in memory as uint32le.
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func (m *MemoryInstance) writeUint32Le(offset uint32, v uint32) bool {
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if !m.hasSize(offset, 4) {
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return false
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}
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binary.LittleEndian.PutUint32(m.Buffer[offset:], v)
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return true
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}
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// writeUint64Le implements WriteUint64Le without using a context. This is extracted as both ints and floats are stored
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// in memory as uint64le.
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func (m *MemoryInstance) writeUint64Le(offset uint32, v uint64) bool {
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if !m.hasSize(offset, 8) {
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return false
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}
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binary.LittleEndian.PutUint64(m.Buffer[offset:], v)
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return true
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}
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// Wait32 suspends the caller until the offset is notified by a different agent.
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func (m *MemoryInstance) Wait32(offset uint32, exp uint32, timeout int64, reader func(mem *MemoryInstance, offset uint32) uint32) uint64 {
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w := m.getWaiters(offset)
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w.mux.Lock()
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cur := reader(m, offset)
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if cur != exp {
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w.mux.Unlock()
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return 1
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}
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return m.wait(w, timeout)
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}
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// Wait64 suspends the caller until the offset is notified by a different agent.
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func (m *MemoryInstance) Wait64(offset uint32, exp uint64, timeout int64, reader func(mem *MemoryInstance, offset uint32) uint64) uint64 {
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w := m.getWaiters(offset)
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w.mux.Lock()
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cur := reader(m, offset)
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if cur != exp {
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w.mux.Unlock()
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return 1
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}
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return m.wait(w, timeout)
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}
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func (m *MemoryInstance) wait(w *waiters, timeout int64) uint64 {
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if w.l == nil {
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w.l = list.New()
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}
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// The specification requires a trap if the number of existing waiters + 1 == 2^32, so we add a check here.
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// In practice, it is unlikely the application would ever accumulate such a large number of waiters as it
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// indicates several GB of RAM used just for the list of waiters.
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// https://github.com/WebAssembly/threads/blob/main/proposals/threads/Overview.md#wait
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if uint64(w.l.Len()+1) == 1<<32 {
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w.mux.Unlock()
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panic(wasmruntime.ErrRuntimeTooManyWaiters)
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}
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ready := make(chan struct{})
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elem := w.l.PushBack(ready)
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w.mux.Unlock()
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if timeout < 0 {
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<-ready
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return 0
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} else {
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select {
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case <-ready:
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return 0
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case <-time.After(time.Duration(timeout)):
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// While we could see if the channel completed by now and ignore the timeout, similar to x/sync/semaphore,
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// the Wasm spec doesn't specify this behavior, so we keep things simple by prioritizing the timeout.
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w.mux.Lock()
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w.l.Remove(elem)
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w.mux.Unlock()
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return 2
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}
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}
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}
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func (m *MemoryInstance) getWaiters(offset uint32) *waiters {
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wAny, ok := m.waiters.Load(offset)
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if !ok {
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// The first time an address is waited on, simultaneous waits will cause extra allocations.
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// Further operations will be loaded above, which is also the general pattern of usage with
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// mutexes.
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wAny, _ = m.waiters.LoadOrStore(offset, &waiters{})
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}
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return wAny.(*waiters)
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}
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// Notify wakes up at most count waiters at the given offset.
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func (m *MemoryInstance) Notify(offset uint32, count uint32) uint32 {
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wAny, ok := m.waiters.Load(offset)
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if !ok {
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return 0
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}
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w := wAny.(*waiters)
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w.mux.Lock()
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defer w.mux.Unlock()
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if w.l == nil {
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return 0
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}
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res := uint32(0)
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for num := w.l.Len(); num > 0 && res < count; num = w.l.Len() {
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w := w.l.Remove(w.l.Front()).(chan struct{})
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close(w)
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res++
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}
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return res
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}
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