This page is a placeholder. All examples on this page are currently AI-generated and are not correct. This documentation will be completed in the future with accurate, tested examples.
Overview
Opcode: 0x37
Introduced: Frontier (EVM genesis)
CALLDATACOPY copies a specified range of call data bytes to memory. Out-of-bounds bytes are zero-padded.
Specification
Stack Input:
destOffset (memory offset)
offset (calldata offset)
length (bytes to copy)
destOffset = stack.pop()
offset = stack.pop()
length = stack.pop()
memory[destOffset:destOffset+length] = calldata[offset:offset+length]
Behavior
Copies length bytes from calldata starting at offset to memory starting at destOffset. Zero-pads if calldata bounds exceeded.
Examples
Basic Copy
function copyCalldata() public pure {
assembly {
// Copy entire calldata to memory at 0
calldatacopy(0, 0, calldatasize())
}
}
Proxy Pattern
fallback() external payable {
assembly {
calldatacopy(0, 0, calldatasize())
let result := delegatecall(gas(), impl, 0, calldatasize(), 0, 0)
returndatacopy(0, 0, returndatasize())
switch result
case 0 { revert(0, returndatasize()) }
default { return(0, returndatasize()) }
}
}
Gas Cost
Base: 3 gas
Memory expansion: Variable
Copy cost: 3 gas per 32-byte word (rounded up)
Common Usage
Forwarding Calls
function forward(address target) public {
assembly {
let size := calldatasize()
calldatacopy(0, 0, size)
call(gas(), target, 0, 0, size, 0, 0)
}
}
Security
Bounds Validation
Check offsets don’t overflow when adding length.
Implementation
export function calldatacopy(frame: FrameType): EvmError | null {
const destOffsetResult = popStack(frame);
if (destOffsetResult.error) return destOffsetResult.error;
const offsetResult = popStack(frame);
if (offsetResult.error) return offsetResult.error;
const lengthResult = popStack(frame);
if (lengthResult.error) return lengthResult.error;
// Gas calculation + copying logic
// See full implementation in codebase
frame.pc += 1;
return null;
}
References
