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# EVMC – Ethereum Client-VM Connector API {#mainpage}
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2018-09-06 14:13:45 +00:00
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The EVMC is the low-level ABI between Ethereum Virtual Machines (EVMs) and
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2018-10-23 16:52:34 +00:00
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Ethereum Clients. On the EVM-side it supports classic EVM1 and [ewasm].
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On the Client-side it defines the interface for EVM implementations
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to access Ethereum environment and state.
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2018-10-05 14:28:32 +00:00
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# Guides
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- [Host Implementation Guide](@ref hostguide)
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- [VM Implementation Guide](@ref vmguide)
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2018-09-06 14:13:45 +00:00
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# Versioning {#versioning}
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The EVMC project uses [Semantic Versioning](https://semver.org).
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Moreover, the _MAJOR_ version number is also referenced as the EVMC ABI version.
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This ABI version is available to VM and Host implementations by ::EVMC_ABI_VERSION.
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For example EVMC 3.2.1 would have ABI version 3 and therefore this project release
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can be referenced as EVMC ABIv3 or just EVMC 3.
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# Modules
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- [EVMC](@ref EVMC)
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– the main component that defines API for VMs and Clients (Hosts).
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- [EVMC Loader](@ref loader)
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– the library for loading VMs implemented as Dynamically Loaded Libraries (DLLs, shared objects).
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- [EVMC Helpers](@ref helpers)
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– a collection of utility functions for easier integration with EVMC.
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- [EVM Instructions](@ref instructions)
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– the library with collection of metrics for EVM1 instruction set.
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- [EVMC VM Tester](@ref vmtester)
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– the EVMC-compatibility testing tool for VM implementations.
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2018-10-23 16:52:34 +00:00
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[ewasm]: https://github.com/ewasm/design
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@addtogroup EVMC
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## Terms
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1. **VM** – An Ethereum Virtual Machine instance/implementation.
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2. **Host** – An entity controlling the VM.
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The Host requests code execution and responses to VM queries by callback
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functions. This usually represents an Ethereum Client.
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2018-08-13 15:09:02 +00:00
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## Responsibilities
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### VM
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- Executes the code (obviously).
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- Calculates the running gas cost and manages the gas counter except the refund
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counter.
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- Controls the call depth, including the exceptional termination of execution
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in case the maximum depth is reached.
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### Host
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- Provides access to State.
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- Creates new accounts (with code being a result of VM execution).
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- Handles refunds entirely.
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- Manages the set of precompiled contracts and handles execution of messages
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coming to them.
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