💡Ethereum Virtual Machine (EVM) Concepts:
· Accounts types
· Transactions
· Gas
· Storage
· Memory
· Stack
· Stack complex operations
· Instruction Set
· Message Calls
· Delegatecall
· Logs
· Create calls
· Self-destruct
· Deactivate and
· Precompiled Contracts
↓
· Accounts types
· Transactions
· Gas
· Storage
· Memory
· Stack
· Stack complex operations
· Instruction Set
· Message Calls
· Delegatecall
· Logs
· Create calls
· Self-destruct
· Deactivate and
· Precompiled Contracts
↓
ACCOUNT TYPES:
- External accounts: controlled by public-private key pairs, address determined from the public key.
- Contract accounts: controlled by the code stored with the account, address determined at the creation time.
- External accounts: controlled by public-private key pairs, address determined from the public key.
- Contract accounts: controlled by the code stored with the account, address determined at the creation time.
TRANSACTIONS
Messages sent from one account to another one
It can include:
- Binary data (payload)
- Ether
If the target account contains code, that code is executed. The payload is provided as input data.
If the target account is not set, a new contract is created.
Messages sent from one account to another one
It can include:
- Binary data (payload)
- Ether
If the target account contains code, that code is executed. The payload is provided as input data.
If the target account is not set, a new contract is created.
GAS
A transaction is charged with gas.
First, a gas price is set by the creator, at gas_price * gas cost.
If some gas is left after the execution, it's refunded.
If the gas is used up at any point, an exception is triggered, and all the modifications are reverted.
A transaction is charged with gas.
First, a gas price is set by the creator, at gas_price * gas cost.
If some gas is left after the execution, it's refunded.
If the gas is used up at any point, an exception is triggered, and all the modifications are reverted.
STORAGE
It's a key-value store that maps 256-bit words to 256-bit words.
Each account has persistent storage between function calls and transactions.
It's not possible to enumerate storage from within a contract, it's costly to read, and even more to initialize and modify it.
It's a key-value store that maps 256-bit words to 256-bit words.
Each account has persistent storage between function calls and transactions.
It's not possible to enumerate storage from within a contract, it's costly to read, and even more to initialize and modify it.
MEMORY
Contract's space instance for each message call.
Memory can be addressed at byte level:
- Reads are limited to 256 bits
- Writes can be 8 bits or 256 bits
Memory is expanded on access by a 256-bit, the gas cost must be paid at expansions time (it scales quadratically).
Contract's space instance for each message call.
Memory can be addressed at byte level:
- Reads are limited to 256 bits
- Writes can be 8 bits or 256 bits
Memory is expanded on access by a 256-bit, the gas cost must be paid at expansions time (it scales quadratically).
STACK
The EVM is a stack machine: all computations are performed on a data area (the stack).
Maximum size of 1024 elements with 256-bits words
Possible actions:
- copy one of the topmost 16 elements to the top of the stack
- swap the topmost element with one of the 16 below.
The EVM is a stack machine: all computations are performed on a data area (the stack).
Maximum size of 1024 elements with 256-bits words
Possible actions:
- copy one of the topmost 16 elements to the top of the stack
- swap the topmost element with one of the 16 below.
STACK COMPLEX OPERATIONS
Other operations take the topmost 2 elements from the stack and push the result onto it.
Stack elements can be moved to storage/memory to get deeper access
It's not possible to just access arbitrary elements in the stack without first removing the top
Other operations take the topmost 2 elements from the stack and push the result onto it.
Stack elements can be moved to storage/memory to get deeper access
It's not possible to just access arbitrary elements in the stack without first removing the top
INSTRUCTION SET
All instructions operate on 256-bit words, or on memory slices.
Arithmetic, bit, logical, comparison operations are present.
Conditional/unconditional jumps are possible.
Contracts can access relevant properties of the current block (number, timestamp, ...).
All instructions operate on 256-bit words, or on memory slices.
Arithmetic, bit, logical, comparison operations are present.
Conditional/unconditional jumps are possible.
Contracts can access relevant properties of the current block (number, timestamp, ...).
MESSAGE CALLS
Similarly transactions, they have:
- source
- target
- data
- payload
- Ether
- gas
- return data
A transaction is a top-level msg call that can create further message calls.
Contracts can call other contracts or send Ether to non-contract accounts with msg calls
Similarly transactions, they have:
- source
- target
- data
- payload
- Ether
- gas
- return data
A transaction is a top-level msg call that can create further message calls.
Contracts can call other contracts or send Ether to non-contract accounts with msg calls
DELEGATECALL
It's a msg call variant, BUT:
- target address code executed on calling the contract context
- msg.sender/msg.value don't change values
A contract can dynamically load code from a different address at runtime
Storage, address, balance refer to the calling contract
It's a msg call variant, BUT:
- target address code executed on calling the contract context
- msg.sender/msg.value don't change values
A contract can dynamically load code from a different address at runtime
Storage, address, balance refer to the calling contract
LOGS
Data can be stored in a specially indexed data structure that maps all the way up to the block level.
Contracts cannot access log data after creation, but they can be efficiently accessed from outside the blockchain.
This feature is used by Solidity to implement events.
Data can be stored in a specially indexed data structure that maps all the way up to the block level.
Contracts cannot access log data after creation, but they can be efficiently accessed from outside the blockchain.
This feature is used by Solidity to implement events.
CREATE CALLS
Contracts can create other contracts using a special opcode.
Differences between create calls and normal message calls:
- the payload data is executed
- the result is stored as code
- the caller/creator receives the address of the new contract on the stack
Contracts can create other contracts using a special opcode.
Differences between create calls and normal message calls:
- the payload data is executed
- the result is stored as code
- the caller/creator receives the address of the new contract on the stack
SELF DESTRUCT
Operation on contract's address to remove code from the blockchain
- the Ether is sent to a designated target
- storage and code are removed from the state
Removing the contract is dangerous: if someone sends Ether to removed contracts, the Ether is lost.
Operation on contract's address to remove code from the blockchain
- the Ether is sent to a designated target
- storage and code are removed from the state
Removing the contract is dangerous: if someone sends Ether to removed contracts, the Ether is lost.
DEACTIVATE
If you want to deactivate your contracts, you should instead disable them by changing some internal state which causes all functions to revert. This makes it impossible to use the contract, as it returns Ether immediately.
If you want to deactivate your contracts, you should instead disable them by changing some internal state which causes all functions to revert. This makes it impossible to use the contract, as it returns Ether immediately.
PRECOMPILED CONTRACTS
Contract addresses with ranges 1-8 are special.
They can be called like any other contract, but their behavior and gas cost is not defined by EVM code stored at that address but implemented in the EVM execution environment itself.
Src: Solidity docs.
Contract addresses with ranges 1-8 are special.
They can be called like any other contract, but their behavior and gas cost is not defined by EVM code stored at that address but implemented in the EVM execution environment itself.
Src: Solidity docs.
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