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Use invalid opcode as part of the eWASM magic #39

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4 changes: 3 additions & 1 deletion backwardsCompatibility.md
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Expand Up @@ -14,7 +14,9 @@ cost. The fee schedule for eWASM is yet to be specified.
## Identification of code
We assume there is some sort of code handler function that all clients have
implemented. The code handler identifies the instruction set type by whether it
starts with WASM's magic number or not.
starts with the *eWASM preamble* or not.

The *eWASM preamble* consists of an invalid EVM1 opcode (`0xEF`) followed by the WASM magic number.

The WASM magic number is the following byte sequence: `0x00, 0x61, 0x73, 0x6d`.

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2 changes: 2 additions & 0 deletions contract_interface.md
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Expand Up @@ -6,6 +6,8 @@ The eWASM Contract Interface (ECI) specifies the structure of a contract module.

Every contract must be stored in the [WebAssembly Binary Encoding](https://github.com/WebAssembly/design/blob/master/BinaryEncoding.md) format (in short, WASM bytecode).

The WASM bytecode must be prefixed with an invalid EVM1 opcode (`0xEF`).

### Imports

A contract can only import symbols specified in the [Ethereum Environment Interface](./eth_interface.md).
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