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I have gone through and updated all existing EIPs to match this rule, including EIP-1. In some cases, people were using markdown citations, I suspect because the long-form was a bit verbose to inline. Since the relative path is quite short, I moved these to inline but I wouldn't be opposed to putting them back to citation format if that is desired by the authors. In doing the migration/cleanup, I found some EIP references to EIPs that don't actually exist. In these cases I tried to excise the reference from the EIP as best I could. It is worth noting that the Readme actually already had this rule, it just wasn't expressed properly in EIP-1 and the "Citation Format" section of the readme I think caused people a bit of confusion (when citing externally, you should use the citation format).
42 lines
3.0 KiB
Markdown
42 lines
3.0 KiB
Markdown
---
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eip: 2327
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title: BEGINDATA opcode
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author: Martin Lundfall (@MrChico)
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discussions-to: https://ethereum-magicians.org/t/new-opcode-begindata/3727
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status: Draft
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type: Standards Track
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category: Core
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created: 2019-10-28
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---
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## Simple Summary
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Introduces a new opcode `BEGINDATA`, which indicates that the remaining bytes of the contract should be regarded as data rather than contract code.
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## Abstract
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It is common for smart contracts to efficiently store data directly in the contract bytecode. Examples include constant variables, compiler metadata and the contract runtime during the init phase. Currently, such data is not distinguished from normal bytecode and is still being analysed for `JUMPDEST`s by EVM interpreters. This EIP introduces a new opcode `BEGINDATA` at byte `0xb6`, which marks the remainding bytecode as data, indicating to EVM interpreters, static analysis tools and chain explorers that the remaining bytes do not represent opcodes.
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## Motivation
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The `BEGINDATA` opcode has been suggested before as part of the EIP `Subroutines and Static Jumps for the EVM` [EIP-615](./eip-615.md) as a way to determine the position of jumptables in contract bytecode. It is here introduced in its own right in order to exclude data from the `JUMPDEST` analysis of contracts, making it impossible to jump to data. This makes it easier for static analysis tools to analyse contracts, allows disassemblers, chain explorers and debuggers to not display data as a mess of INVALID opcodes and may even provide a marginal improvement in performance. Additionally, it paves the way for suggestions such as [EIP-1712](https://github.com/ethereum/EIPs/pull/1712) to disallow unused opcodes, jumptables [EIP-615](./eip-615.md) and speculative proposals to disallow for deployment of contracts with stack usage violations.
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## Specification
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While computing the valid `JUMPDEST`s of a contract, halt analysis if `BEGINDATA` is encountered. A `JUMP` to a value higher than the `PC` value of `BEGINDATA` should throw with a `BAD_JUMP_DESTINATION` error. Bytes past `BEGINDATA` remain accessible via `CODECOPY` and `EXTCODECOPY`.
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If `BEGINDATA` is encountered during contract execution, it has the same semantics as `STOP`. It uses 0 gas.
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## Rationale
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The byte `0xb6` was chosen to align with [EIP-615](./eip-615.md).
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The choice to `STOP` if `BEGINDATA` is encountered is somewhat arbitrary. An alternative would be to be to abort the execution with an out-of-gas error.
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## Backwards Compatibility
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The proposal will not change any existing contracts unless their current behaviour relies upon the usage of unused opcodes.
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## Test Cases
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Test cases should include:
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1) A contract which jumps to a destination `X`, where `X` has a pc value higher than the `BEGINDATA` opcode, and the byte at `X` is `0x5b`. This should fail with a `BAD_JUMP_DESTINATION` error.
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2) A contract which encounters the `BEGINDATA` opcode (should stop executing the current call frame)
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## Implementation
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Not yet.
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## Copyright
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Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
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