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EIP-2003 - EVMC modules for implementations of precompiled contracts (#2003)
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Paweł Bylica
Nick Savers
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---
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eip: 2003
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title: EVMC modules for implementations of precompiled contracts
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author: Paweł Bylica (@chfast), Alex Beregszaszi (@axic)
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discussions-to: https://github.com/ethereum/evmc/issues/259
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status: Draft
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type: Informational
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created: 2019-05-09
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requires: 1352
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---
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## Abstract
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[EVMC] specifies a generic API for Ethereum execution engines.
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This EIP specifies a way of providing implementations of Ethereum precompiled contracts
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using the [EVMC VM API].
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## Specification
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For the complete [EVMC] specification visit the [EVMC documentation] first.
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This EIP is based on and is compatible with EVMC ABI version 6.
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The EVMC module with implementations of precompiled contracts SHOULD:
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1. Advertise the [`EVMC_CAPABILITY_PRECOMPILES`] capability
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in the [`get_capabilities()`] method.
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2. Implement the [`execute()`] method in the following way:
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1. Validate the incoming execution request requirements:
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1. The message kind ([`evmc_message::kind`]) is a call ([`EVMC_CALL`]).
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2. The call destination address ([`evmc_message::destination`])
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is within the range of precompiled contracts defined by [EIP-1352].
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3. There is no code provided (the `code` argument is `NULL` and `code_size` argument is `0`).
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If the requirements are not fulfilled, abort execution with the [`EVMC_REJECTED`] status code.
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2. Check if the call destination address ([`evmc_message::destination`])
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targets existing precompiled contract.
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Consider the EVM revision ([`evmc_revision`]) requested by
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the `rev` parameter of [`execute()`].
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If yes, execute as follows:
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1. Inspect the input data ([`evmc_message::input_data`], [`evmc_message::input_size`])
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and calculate the _gas cost_ of the execution.
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2. Compute the amount of _gas left_ after execution by
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subtracting the _gas cost_ from the call gas limit ([`evmc_message::gas`]).
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3. If _gas left_ is negative,
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abort execution with the [`EVMC_OUT_OF_GAS`] status code.
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4. Otherwise,
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execute the code of the precompiled contract,
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return the [`EVMC_SUCCESS`] status code, the output and _gas left_
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([`evmc_result::output_data`], [`evmc_result::output_size`], [`evmc_result::gas_left`]).
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3. Otherwise, emulate execution of empty code by returning
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the [`EVMC_SUCCESS`] status code
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and _gas left_ equal the call gas limit ([`evmc_message::gas`]).
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Precompiled contract implementations are allowed to return two more EVMC error codes:
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- [`EVMC_FAILURE`] if the failure was caused due to something other than out of gas (e.g. input validation error)
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- [`EVMC_REVERT`] if the precompile doesn't want to forfeit all supplied gas (as of May 2019 no such precompile exists)
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The Client is not required to provide the Host interface ([`evmc_context`] argument of [`execute()`] is set to NULL).
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Therefore, the precompiled contracts implementation MUST NOT access the `evmc_context`.
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## Rationale
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It is very unlikely that any precompile will need to access or modify a contract state.
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Not requiring the Client to implement the EVMC Host interface removes the big portion of work
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needed for full EVMC integration.
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## Test Cases
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EVMC provides the [evmc-vmtester] tool for checking compatibility with the EVMC specification.
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## Implementations
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- [Example of Precompiles VM implementation][example_precompiles_vm.cpp]
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- [ewasm precompiles]
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- Aleth code for precompiles
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- Parity code for precompiles
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- [EIP-1962 implemented as an EVMC precompile module](https://github.com/axic/eip1962-evmc)
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## References
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- [EVMC – Ethereum Client-VM Connector API][EVMC]
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- [EVMC documentation]
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- [EVMC VM Implementation Guide][EVMC VM API]
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- [EIP 1352: Specify restricted address range for precompiles/system contracts][EIP-1352]
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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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[EIP-1352]: https://eips.ethereum.org/EIPS/eip-1352
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[EVMC]: https://github.com/ethereum/evmc
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[EVMC documentation]: https://ethereum.github.io/evmc/
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[EVMC VM API]: https://ethereum.github.io/evmc/vmguide.html
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[evmc-vmtester]: https://ethereum.github.io/evmc/vmtester.html
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[example_precompiles_vm.cpp]: https://github.com/ethereum/evmc/blob/master/examples/example_precompiles_vm/example_precompiles_vm.cpp
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[ewasm precompiles]: https://github.com/ewasm/ewasm-precompiles
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[`EVMC_CALL`]: https://ethereum.github.io/evmc/group__EVMC.html#ggab2fa68a92a6828064a61e46060abc634abcf3ae29d9a88ff70b98374fc665694a
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[`EVMC_CAPABILITY_PRECOMPILES`]: https://ethereum.github.io/evmc/group__EVMC.html#gga44f9ecb88cf6422a0072936494fd6ac7a43ea2aa7b099a2d67bc53c118ff3683d
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[`EVMC_FAILURE`]: https://ethereum.github.io/evmc/group__EVMC.html#gga4c0be97f333c050ff45321fcaa34d920aed5b2a4afa5a47af732569445920a4a9
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[`EVMC_OUT_OF_GAS`]: https://ethereum.github.io/evmc/group__EVMC.html#gga4c0be97f333c050ff45321fcaa34d920abfc47f75656c996c0b29c0553c00fc18
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[`EVMC_REJECTED`]: https://ethereum.github.io/evmc/group__EVMC.html#gga4c0be97f333c050ff45321fcaa34d920a2f3e0d8777f8d974ead27ae2a6eb2005
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[`EVMC_REVERT`]: https://ethereum.github.io/evmc/group__EVMC.html#gga4c0be97f333c050ff45321fcaa34d920aed708e84d49cc1270e54ec20b0ca0a05
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[`EVMC_SUCCESS`]: https://ethereum.github.io/evmc/group__EVMC.html#gga4c0be97f333c050ff45321fcaa34d920a4bc3069fec2bab2a55355a72b7db68b7
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[`execute()`]: https://ethereum.github.io/evmc/structevmc__instance.html#a0823ebff21f9b0395b157e8c6b14a207
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[`get_capabilities()`]: https://ethereum.github.io/evmc/structevmc__instance.html#ae63b9ca898aa41cbd1e2fe86ca8f4e1c
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[`evmc_message::destination`]: https://ethereum.github.io/evmc/structevmc__message.html#a88ecfaa03a85a31c6da36fa043b98cea
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[`evmc_message::input_data`]: https://ethereum.github.io/evmc/structevmc__message.html#a1adee3454b105eb29cd659ee0cf65c77
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[`evmc_message::input_size`]: https://ethereum.github.io/evmc/structevmc__message.html#a2cf1deebd0dbbb20f25ecdfa299f4b5d
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[`evmc_message::gas`]: https://ethereum.github.io/evmc/structevmc__message.html#ae8deff46588584fa27890e74c82db5e7
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[`evmc_message::kind`]: https://ethereum.github.io/evmc/structevmc__message.html#a691cb93e81d6dfd4fd7e2fa3d06a6bfa
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[`evmc_result::gas_left`]: https://ethereum.github.io/evmc/structevmc__result.html#af8478c93dbcc3cb2876037c5a5afd4c0
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[`evmc_result::output_data`]: https://ethereum.github.io/evmc/structevmc__result.html#a61978e85f9d795a7b9695b9cbf1748d6
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[`evmc_result::output_size`]: https://ethereum.github.io/evmc/structevmc__result.html#a93bb7419aff492cdef754421c6d74e26
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[`evmc_revision`]: https://ethereum.github.io/evmc/group__EVMC.html#gae5759b1590071966ccf6a505b52a0ef7
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