github.com/tetratelabs/wazero@v1.7.3-0.20240513003603-48f702e154b5/internal/wasm/binary/const_expr.go (about)

     1  package binary
     2  
     3  import (
     4  	"bytes"
     5  	"fmt"
     6  	"io"
     7  
     8  	"github.com/tetratelabs/wazero/api"
     9  	"github.com/tetratelabs/wazero/internal/ieee754"
    10  	"github.com/tetratelabs/wazero/internal/leb128"
    11  	"github.com/tetratelabs/wazero/internal/wasm"
    12  )
    13  
    14  func decodeConstantExpression(r *bytes.Reader, enabledFeatures api.CoreFeatures, ret *wasm.ConstantExpression) error {
    15  	b, err := r.ReadByte()
    16  	if err != nil {
    17  		return fmt.Errorf("read opcode: %v", err)
    18  	}
    19  
    20  	remainingBeforeData := int64(r.Len())
    21  	offsetAtData := r.Size() - remainingBeforeData
    22  
    23  	opcode := b
    24  	switch opcode {
    25  	case wasm.OpcodeI32Const:
    26  		// Treat constants as signed as their interpretation is not yet known per /RATIONALE.md
    27  		_, _, err = leb128.DecodeInt32(r)
    28  	case wasm.OpcodeI64Const:
    29  		// Treat constants as signed as their interpretation is not yet known per /RATIONALE.md
    30  		_, _, err = leb128.DecodeInt64(r)
    31  	case wasm.OpcodeF32Const:
    32  		buf := make([]byte, 4)
    33  		if _, err := io.ReadFull(r, buf); err != nil {
    34  			return fmt.Errorf("read f32 constant: %v", err)
    35  		}
    36  		_, err = ieee754.DecodeFloat32(buf)
    37  	case wasm.OpcodeF64Const:
    38  		buf := make([]byte, 8)
    39  		if _, err := io.ReadFull(r, buf); err != nil {
    40  			return fmt.Errorf("read f64 constant: %v", err)
    41  		}
    42  		_, err = ieee754.DecodeFloat64(buf)
    43  	case wasm.OpcodeGlobalGet:
    44  		_, _, err = leb128.DecodeUint32(r)
    45  	case wasm.OpcodeRefNull:
    46  		if err := enabledFeatures.RequireEnabled(api.CoreFeatureBulkMemoryOperations); err != nil {
    47  			return fmt.Errorf("ref.null is not supported as %w", err)
    48  		}
    49  		reftype, err := r.ReadByte()
    50  		if err != nil {
    51  			return fmt.Errorf("read reference type for ref.null: %w", err)
    52  		} else if reftype != wasm.RefTypeFuncref && reftype != wasm.RefTypeExternref {
    53  			return fmt.Errorf("invalid type for ref.null: 0x%x", reftype)
    54  		}
    55  	case wasm.OpcodeRefFunc:
    56  		if err := enabledFeatures.RequireEnabled(api.CoreFeatureBulkMemoryOperations); err != nil {
    57  			return fmt.Errorf("ref.func is not supported as %w", err)
    58  		}
    59  		// Parsing index.
    60  		_, _, err = leb128.DecodeUint32(r)
    61  	case wasm.OpcodeVecPrefix:
    62  		if err := enabledFeatures.RequireEnabled(api.CoreFeatureSIMD); err != nil {
    63  			return fmt.Errorf("vector instructions are not supported as %w", err)
    64  		}
    65  		opcode, err = r.ReadByte()
    66  		if err != nil {
    67  			return fmt.Errorf("read vector instruction opcode suffix: %w", err)
    68  		}
    69  
    70  		if opcode != wasm.OpcodeVecV128Const {
    71  			return fmt.Errorf("invalid vector opcode for const expression: %#x", opcode)
    72  		}
    73  
    74  		remainingBeforeData = int64(r.Len())
    75  		offsetAtData = r.Size() - remainingBeforeData
    76  
    77  		n, err := r.Read(make([]byte, 16))
    78  		if err != nil {
    79  			return fmt.Errorf("read vector const instruction immediates: %w", err)
    80  		} else if n != 16 {
    81  			return fmt.Errorf("read vector const instruction immediates: needs 16 bytes but was %d bytes", n)
    82  		}
    83  	default:
    84  		return fmt.Errorf("%v for const expression opt code: %#x", ErrInvalidByte, b)
    85  	}
    86  
    87  	if err != nil {
    88  		return fmt.Errorf("read value: %v", err)
    89  	}
    90  
    91  	if b, err = r.ReadByte(); err != nil {
    92  		return fmt.Errorf("look for end opcode: %v", err)
    93  	}
    94  
    95  	if b != wasm.OpcodeEnd {
    96  		return fmt.Errorf("constant expression has been not terminated")
    97  	}
    98  
    99  	ret.Data = make([]byte, remainingBeforeData-int64(r.Len())-1)
   100  	if _, err = r.ReadAt(ret.Data, offsetAtData); err != nil {
   101  		return fmt.Errorf("error re-buffering ConstantExpression.Data")
   102  	}
   103  	ret.Opcode = opcode
   104  	return nil
   105  }