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Overview

Opcode: 0x36 Introduced: Frontier (EVM genesis) CALLDATASIZE pushes the byte length of the call data (input data) onto the stack.

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Specification

Stack Input: 
[]
Stack Output: 
size (uint256, in bytes)
Gas Cost: 2 (GasQuickStep) Operation: 
stack.push(calldata.length)

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Behavior

CALLDATASIZE returns the total number of bytes in the call data, including function selector. Key characteristics:
  • Returns exact byte count
  • Includes 4-byte function selector (if present)
  • Always >= 0
  • Constant throughout execution

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Examples

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Basic Usage

import { calldatasize } from '@tevm/voltaire/evm/context';
import { createFrame } from '@tevm/voltaire/evm/Frame';

const calldata = new Uint8Array(68); // selector + 2 uint256
const frame = createFrame({ calldata, stack: [] });

const err = calldatasize(frame);

console.log(frame.stack[0]); // 68n

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Validation

contract CalldataValidator {
    function requireMinimumCalldata(uint256 minSize) public pure {
        assembly {
            if lt(calldatasize(), minSize) {
                revert(0, 0)
            }
        }
    }

    function hasArguments() public pure returns (bool) {
        // Function selector = 4 bytes
        // If calldatasize > 4, has arguments
        return msg.data.length > 4;
    }
}

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Gas Cost

Cost: 2 gas (GasQuickStep) Same as ADDRESS, ORIGIN, CALLER, etc.

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Common Usage

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Bounds Checking

function safeDecod() public pure {
    assembly {
        // Ensure enough data for selector + 1 uint256
        if lt(calldatasize(), 36) {
            revert(0, 0)
        }
    }
}

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Copying Entire Calldata

function forwardCalldata(address target) public {
    assembly {
        let size := calldatasize()
        calldatacopy(0, 0, size)
        let result := call(gas(), target, 0, 0, size, 0, 0)
        if iszero(result) { revert(0, 0) }
    }
}

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Security

Safe opcode, no vulnerabilities.

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Implementation

export function calldatasize(frame: FrameType): EvmError | null {
  const gasErr = consumeGas(frame, 2n);
  if (gasErr) return gasErr;

  const pushErr = pushStack(frame, BigInt(frame.calldata.length));
  if (pushErr) return pushErr;

  frame.pc += 1;
  return null;
}

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References