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package binary
import (
"bytes"
"errors"
"fmt"
"github.com/tetratelabs/wazero/api"
"github.com/tetratelabs/wazero/internal/leb128"
"github.com/tetratelabs/wazero/internal/wasm"
)
func ensureElementKindFuncRef(r *bytes.Reader) error {
elemKind, err := r.ReadByte()
if err != nil {
return fmt.Errorf("read element prefix: %w", err)
}
if elemKind != 0x0 { // ElemKind is fixed to 0x0 now: https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#element-section
return fmt.Errorf("element kind must be zero but was 0x%x", elemKind)
}
return nil
}
func decodeElementInitValueVector(r *bytes.Reader) ([]wasm.Index, error) {
vs, _, err := leb128.DecodeUint32(r)
if err != nil {
return nil, fmt.Errorf("get size of vector: %w", err)
}
vec := make([]wasm.Index, vs)
for i := range vec {
u32, _, err := leb128.DecodeUint32(r)
if err != nil {
return nil, fmt.Errorf("read function index: %w", err)
}
if u32 >= wasm.MaximumFunctionIndex {
return nil, fmt.Errorf("too large function index in Element init: %d", u32)
}
vec[i] = u32
}
return vec, nil
}
func decodeElementConstExprVector(r *bytes.Reader, elemType wasm.RefType, enabledFeatures api.CoreFeatures) ([]wasm.Index, error) {
vs, _, err := leb128.DecodeUint32(r)
if err != nil {
return nil, fmt.Errorf("failed to get the size of constexpr vector: %w", err)
}
vec := make([]wasm.Index, vs)
for i := range vec {
var expr wasm.ConstantExpression
err := decodeConstantExpression(r, enabledFeatures, &expr)
if err != nil {
return nil, err
}
switch expr.Opcode {
case wasm.OpcodeRefFunc:
if elemType != wasm.RefTypeFuncref {
return nil, fmt.Errorf("element type mismatch: want %s, but constexpr has funcref", wasm.RefTypeName(elemType))
}
v, _, _ := leb128.LoadUint32(expr.Data)
if v >= wasm.MaximumFunctionIndex {
return nil, fmt.Errorf("too large function index in Element init: %d", v)
}
vec[i] = v
case wasm.OpcodeRefNull:
if elemType != expr.Data[0] {
return nil, fmt.Errorf("element type mismatch: want %s, but constexpr has %s",
wasm.RefTypeName(elemType), wasm.RefTypeName(expr.Data[0]))
}
vec[i] = wasm.ElementInitNullReference
case wasm.OpcodeGlobalGet:
i32, _, _ := leb128.LoadInt32(expr.Data)
// Resolving the reference type from globals is done at instantiation phase. See the comment on
// wasm.elementInitImportedGlobalReferenceType.
vec[i] = wasm.WrapGlobalIndexAsElementInit(wasm.Index(i32))
default:
return nil, fmt.Errorf("const expr must be either ref.null or ref.func but was %s", wasm.InstructionName(expr.Opcode))
}
}
return vec, nil
}
func decodeElementRefType(r *bytes.Reader) (ret wasm.RefType, err error) {
ret, err = r.ReadByte()
if err != nil {
err = fmt.Errorf("read element ref type: %w", err)
return
}
if ret != wasm.RefTypeFuncref && ret != wasm.RefTypeExternref {
return 0, errors.New("ref type must be funcref or externref for element as of WebAssembly 2.0")
}
return
}
const (
// The prefix is explained at https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#element-section
// elementSegmentPrefixLegacy is the legacy prefix and is only valid one before CoreFeatureBulkMemoryOperations.
elementSegmentPrefixLegacy = iota
// elementSegmentPrefixPassiveFuncrefValueVector is the passive element whose indexes are encoded as vec(varint), and reftype is fixed to funcref.
elementSegmentPrefixPassiveFuncrefValueVector
// elementSegmentPrefixActiveFuncrefValueVectorWithTableIndex is the same as elementSegmentPrefixPassiveFuncrefValueVector but active and table index is encoded.
elementSegmentPrefixActiveFuncrefValueVectorWithTableIndex
// elementSegmentPrefixDeclarativeFuncrefValueVector is the same as elementSegmentPrefixPassiveFuncrefValueVector but declarative.
elementSegmentPrefixDeclarativeFuncrefValueVector
// elementSegmentPrefixActiveFuncrefConstExprVector is active whoce reftype is fixed to funcref and indexes are encoded as vec(const_expr).
elementSegmentPrefixActiveFuncrefConstExprVector
// elementSegmentPrefixPassiveConstExprVector is passive whoce indexes are encoded as vec(const_expr), and reftype is encoded.
elementSegmentPrefixPassiveConstExprVector
// elementSegmentPrefixPassiveConstExprVector is active whoce indexes are encoded as vec(const_expr), and reftype and table index are encoded.
elementSegmentPrefixActiveConstExprVector
// elementSegmentPrefixDeclarativeConstExprVector is declarative whoce indexes are encoded as vec(const_expr), and reftype is encoded.
elementSegmentPrefixDeclarativeConstExprVector
)
func decodeElementSegment(r *bytes.Reader, enabledFeatures api.CoreFeatures, ret *wasm.ElementSegment) error {
prefix, _, err := leb128.DecodeUint32(r)
if err != nil {
return fmt.Errorf("read element prefix: %w", err)
}
if prefix != elementSegmentPrefixLegacy {
if err := enabledFeatures.RequireEnabled(api.CoreFeatureBulkMemoryOperations); err != nil {
return fmt.Errorf("non-zero prefix for element segment is invalid as %w", err)
}
}
// Encoding depends on the prefix and described at https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#element-section
switch prefix {
case elementSegmentPrefixLegacy:
// Legacy prefix which is WebAssembly 1.0 compatible.
err = decodeConstantExpression(r, enabledFeatures, &ret.OffsetExpr)
if err != nil {
return fmt.Errorf("read expr for offset: %w", err)
}
ret.Init, err = decodeElementInitValueVector(r)
if err != nil {
return err
}
ret.Mode = wasm.ElementModeActive
ret.Type = wasm.RefTypeFuncref
return nil
case elementSegmentPrefixPassiveFuncrefValueVector:
// Prefix 1 requires funcref.
if err = ensureElementKindFuncRef(r); err != nil {
return err
}
ret.Init, err = decodeElementInitValueVector(r)
if err != nil {
return err
}
ret.Mode = wasm.ElementModePassive
ret.Type = wasm.RefTypeFuncref
return nil
case elementSegmentPrefixActiveFuncrefValueVectorWithTableIndex:
ret.TableIndex, _, err = leb128.DecodeUint32(r)
if err != nil {
return fmt.Errorf("get size of vector: %w", err)
}
if ret.TableIndex != 0 {
if err := enabledFeatures.RequireEnabled(api.CoreFeatureReferenceTypes); err != nil {
return fmt.Errorf("table index must be zero but was %d: %w", ret.TableIndex, err)
}
}
err := decodeConstantExpression(r, enabledFeatures, &ret.OffsetExpr)
if err != nil {
return fmt.Errorf("read expr for offset: %w", err)
}
// Prefix 2 requires funcref.
if err = ensureElementKindFuncRef(r); err != nil {
return err
}
ret.Init, err = decodeElementInitValueVector(r)
if err != nil {
return err
}
ret.Mode = wasm.ElementModeActive
ret.Type = wasm.RefTypeFuncref
return nil
case elementSegmentPrefixDeclarativeFuncrefValueVector:
// Prefix 3 requires funcref.
if err = ensureElementKindFuncRef(r); err != nil {
return err
}
ret.Init, err = decodeElementInitValueVector(r)
if err != nil {
return err
}
ret.Type = wasm.RefTypeFuncref
ret.Mode = wasm.ElementModeDeclarative
return nil
case elementSegmentPrefixActiveFuncrefConstExprVector:
err := decodeConstantExpression(r, enabledFeatures, &ret.OffsetExpr)
if err != nil {
return fmt.Errorf("read expr for offset: %w", err)
}
ret.Init, err = decodeElementConstExprVector(r, wasm.RefTypeFuncref, enabledFeatures)
if err != nil {
return err
}
ret.Mode = wasm.ElementModeActive
ret.Type = wasm.RefTypeFuncref
return nil
case elementSegmentPrefixPassiveConstExprVector:
ret.Type, err = decodeElementRefType(r)
if err != nil {
return err
}
ret.Init, err = decodeElementConstExprVector(r, ret.Type, enabledFeatures)
if err != nil {
return err
}
ret.Mode = wasm.ElementModePassive
return nil
case elementSegmentPrefixActiveConstExprVector:
ret.TableIndex, _, err = leb128.DecodeUint32(r)
if err != nil {
return fmt.Errorf("get size of vector: %w", err)
}
if ret.TableIndex != 0 {
if err := enabledFeatures.RequireEnabled(api.CoreFeatureReferenceTypes); err != nil {
return fmt.Errorf("table index must be zero but was %d: %w", ret.TableIndex, err)
}
}
err := decodeConstantExpression(r, enabledFeatures, &ret.OffsetExpr)
if err != nil {
return fmt.Errorf("read expr for offset: %w", err)
}
ret.Type, err = decodeElementRefType(r)
if err != nil {
return err
}
ret.Init, err = decodeElementConstExprVector(r, ret.Type, enabledFeatures)
if err != nil {
return err
}
ret.Mode = wasm.ElementModeActive
return nil
case elementSegmentPrefixDeclarativeConstExprVector:
ret.Type, err = decodeElementRefType(r)
if err != nil {
return err
}
ret.Init, err = decodeElementConstExprVector(r, ret.Type, enabledFeatures)
if err != nil {
return err
}
ret.Mode = wasm.ElementModeDeclarative
return nil
default:
return fmt.Errorf("invalid element segment prefix: 0x%x", prefix)
}
}
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