ABI coder v1 does not clean dirty array items

Author: Subway2023Created Apr 4, 2024Updated Sep 14, 2026

Labelsbug :bug:documentation :book:codegen errorlow effortlow impactshould have

Description

When using assembly statements to assign a value that exceeds the array range to an array, AbiCoder v1 fails to encode the return value correctly when returning the array. However, AbiCoder v2 does not have this issue.

Environment

Compiler version: 0.8.25
Target EVM version (as per compiler settings): No restrictions
Framework/IDE: Command-line
EVM execution environment / backend / blockchain client: None
Operating system: Linux

Steps to Reproduce

solidity

# If you comment out this line, AbiCoder v2 will be used by default.
pragma abicoder v1;
contract test {
    function f() external returns (uint8[] memory) {
        uint8[] memory x = new uint8[](1);
        assembly {
            mstore(add(x, 0x20), 0x1ff)
        }
        return x;
    }
}

1. Build EVM

bash

git clone [email protected]:ethereum/go-ethereum.git
make all

2. Get function Signatures

bash

solc C.sol --hashes --overwrite -o hashDir

Function signatures:
26121ff0: f()

3. Get bin-runtime

bash

solc  --bin-runtime C.sol --overwrite -o binDir

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

4. Run in the EVM

bash

go-ethereum-1.13.11/build/bin/evm --debug --json --code "bin in binDir" --input 26121ff0 run >test.json

5. Compare output

output from pragma abicoder v1

{"output":"0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000001ff","gasUsed":"0x23e"}

output from pragma abicoder v2

{"output":"0000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000ff","gasUsed":"0x3c9"}

We can observe that after encoding with AbiCoder v1, the elements in the array are 1ff, whereas after encoding with AbiCoder v2, the array elements are ff

Source: argotorg/solidity

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