GoToSocial/vendor/github.com/tetratelabs/wazero/internal/wasm/memory.go

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