data.go

Documentation: github.com/tetratelabs/wazero/internal/wasm/binary

     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/leb128"
    10  	"github.com/tetratelabs/wazero/internal/wasm"
    11  )
    12  
    13  // dataSegmentPrefix represents three types of data segments.
    14  //
    15  // https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#data-section
    16  type dataSegmentPrefix = uint32
    17  
    18  const (
    19  	// dataSegmentPrefixActive is the prefix for the version 1.0 compatible data segment, which is classified as "active" in 2.0.
    20  	dataSegmentPrefixActive dataSegmentPrefix = 0x0
    21  	// dataSegmentPrefixPassive prefixes the "passive" data segment as in version 2.0 specification.
    22  	dataSegmentPrefixPassive dataSegmentPrefix = 0x1
    23  	// dataSegmentPrefixActiveWithMemoryIndex is the active prefix with memory index encoded which is defined for futur use as of 2.0.
    24  	dataSegmentPrefixActiveWithMemoryIndex dataSegmentPrefix = 0x2
    25  )
    26  
    27  func decodeDataSegment(r *bytes.Reader, enabledFeatures api.CoreFeatures, ret *wasm.DataSegment) (err error) {
    28  	dataSegmentPrefx, _, err := leb128.DecodeUint32(r)
    29  	if err != nil {
    30  		err = fmt.Errorf("read data segment prefix: %w", err)
    31  		return
    32  	}
    33  
    34  	if dataSegmentPrefx != dataSegmentPrefixActive {
    35  		if err = enabledFeatures.RequireEnabled(api.CoreFeatureBulkMemoryOperations); err != nil {
    36  			err = fmt.Errorf("non-zero prefix for data segment is invalid as %w", err)
    37  			return
    38  		}
    39  	}
    40  
    41  	switch dataSegmentPrefx {
    42  	case dataSegmentPrefixActive,
    43  		dataSegmentPrefixActiveWithMemoryIndex:
    44  		// Active data segment as in
    45  		// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#data-section
    46  		if dataSegmentPrefx == 0x2 {
    47  			d, _, err := leb128.DecodeUint32(r)
    48  			if err != nil {
    49  				return fmt.Errorf("read memory index: %v", err)
    50  			} else if d != 0 {
    51  				return fmt.Errorf("memory index must be zero but was %d", d)
    52  			}
    53  		}
    54  
    55  		err = decodeConstantExpression(r, enabledFeatures, &ret.OffsetExpression)
    56  		if err != nil {
    57  			return fmt.Errorf("read offset expression: %v", err)
    58  		}
    59  	case dataSegmentPrefixPassive:
    60  		// Passive data segment doesn't need const expr nor memory index encoded.
    61  		// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/binary/modules.html#data-section
    62  		ret.Passive = true
    63  	default:
    64  		err = fmt.Errorf("invalid data segment prefix: 0x%x", dataSegmentPrefx)
    65  		return
    66  	}
    67  
    68  	vs, _, err := leb128.DecodeUint32(r)
    69  	if err != nil {
    70  		err = fmt.Errorf("get the size of vector: %v", err)
    71  		return
    72  	}
    73  
    74  	ret.Init = make([]byte, vs)
    75  	if _, err = io.ReadFull(r, ret.Init); err != nil {
    76  		err = fmt.Errorf("read bytes for init: %v", err)
    77  	}
    78  	return
    79  }
    80
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