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rskip title description status purpose author layer complexity created
171
Clean EVM Internal Buffer in Call-like Opcodes
Accepted
Usa
FJ (@fedejinich)
Core
1
2020-02-09

Clean EVM Internal Buffer in Call-like Opcodes

RSKIP 171
Title Clean EVM Internal Buffer in Call-like Opcodes
Created 02-09-2020
Author FJ
Purpose Usa
Layer Core
Complexity 1
Status Accepted

Abstract

The purpose of this RSKIP is to make RSK fully compatible with EIP-211. RETURNDATACOPY and RETURNDATASIZE opcodes have already been implemented in previous RSKIPs, but still, there were some corner cases related to call-like opcodes that weren't implemented in previous network upgrades.

Now with this RSKIP we have a mechanism to allow returning arbitrary-length data inside the EVM (EIP-211).

Motivation

Described at EIP-211.

Specification

This RSKIP will be enabled only if block.number >= IRIS_HARD_FORK.

Any opcode that creates a new call frame will be mentioned as call-like opcode

Considered call-like opcodes:

  • OP_CALL
  • OP_CALLCODE
  • OP_DELEGATECALL
  • OP_STATICCALL
  • Further call-like opcodes may be added in future RSKIPs

Since most of the parts of mentioned EIP have already been implemented, this proposal only points to implement this described behaviour:

If the call-like opcode is executed but does not really instantiate a call frame (for example due to insufficient funds for a value transfer or if the called contract does not exist), the return data buffer is empty.

Reproducing misbehaviour

    // Considering this contract invocation call at 0x471fd3ad3e9eeadeec4608b92d16ce6b500704cc
    PUSH1 0x10
    PUSH1 0x05
    ADD
    PUSH1 0x40
    MSTORE
    PUSH1 0x20
    PUSH1 0x40
    RETURN

    // And this EVM execution
    PUSH1 0x20                                          // return size is 32 bytes
    PUSH1 0x40                                          // on free memory pointer
    PUSH1 0x00                                          // no argument
    PUSH1 0x00                                          // no argument size
    PUSH20 0x471fd3ad3e9eeadeec4608b92d16ce6b500704cc   // suppose a valid contract
    PUSH4 0x005B8D80                                    // with some gas
    STATICCALL                                          // call it (call-like opcode)! internal buffer should be 0x15
    PUSH1 0x20                                          // now do the same...
    PUSH1 0x40                                          // on free memory pointer
    PUSH1 0x00                                          // no argument
    PUSH1 0x00                                          // no argument size
    PUSH1 0x00                                          // but call a non-existent contract (this won't produce a new call frame)
    PUSH4 0x005B8D80                                    // with some gas
    STATICCALL                                          // call it (call-like opcode)!

Internal buffer should be 0x00 when RSKIP171 is enabled. If RSKIP171 is disabled and you execute any call-like opcode, the internal state buffer will remain the same, even if that execution didn't produce any new call frame.

Backwards Compatibility

Apart from the described behaviour for call-like opcodes, this proposal stays fully backwards compatible.

References

[1] EIP-211 https://github.com/ethereum/EIPs/blob/master/EIPS/eip-211.md

Copyright

Copyright and related rights waived via CC0.