fb0b311844
Global constants can be defined in wasm or in ModuleBuilder. In either case, they end up being decoded and interpreted during instantiation. This chooses signed encoding to avoid surprises. A more comprehensive explanation was added to RATIONALE.md, but the motivation was a global 100 coming out negative. Signed-off-by: Adrian Cole <adrian@tetrate.io>
58 lines
1.6 KiB
Go
58 lines
1.6 KiB
Go
package binary
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import (
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"bytes"
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"fmt"
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"github.com/tetratelabs/wazero/internal/ieee754"
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"github.com/tetratelabs/wazero/internal/leb128"
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"github.com/tetratelabs/wazero/internal/wasm"
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)
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func decodeConstantExpression(r *bytes.Reader) (*wasm.ConstantExpression, error) {
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b, err := r.ReadByte()
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if err != nil {
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return nil, fmt.Errorf("read opcode: %v", err)
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}
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remainingBeforeData := int64(r.Len())
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offsetAtData := r.Size() - remainingBeforeData
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opcode := b
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switch opcode {
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case wasm.OpcodeI32Const:
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// Treat constants as signed as their interpretation is not yet known per /RATIONALE.md
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_, _, err = leb128.DecodeInt32(r)
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case wasm.OpcodeI64Const:
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// Treat constants as signed as their interpretation is not yet known per /RATIONALE.md
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_, _, err = leb128.DecodeInt64(r)
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case wasm.OpcodeF32Const:
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_, err = ieee754.DecodeFloat32(r)
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case wasm.OpcodeF64Const:
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_, err = ieee754.DecodeFloat64(r)
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case wasm.OpcodeGlobalGet:
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_, _, err = leb128.DecodeUint32(r)
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default:
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return nil, fmt.Errorf("%v for const expression opt code: %#x", ErrInvalidByte, b)
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}
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if err != nil {
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return nil, fmt.Errorf("read value: %v", err)
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}
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if b, err = r.ReadByte(); err != nil {
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return nil, fmt.Errorf("look for end opcode: %v", err)
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}
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if b != wasm.OpcodeEnd {
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return nil, fmt.Errorf("constant expression has been not terminated")
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}
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data := make([]byte, remainingBeforeData-int64(r.Len()))
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if _, err := r.ReadAt(data, offsetAtData); err != nil {
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return nil, fmt.Errorf("error re-buffering ConstantExpression.Data")
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}
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return &wasm.ConstantExpression{Opcode: opcode, Data: data}, nil
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}
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