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Add EIP: EOF/EVM Trace Specification
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---
eip: 7756
title: EOF/EVM Trace Specification
description: Updates EIP-3155 tracing to add EOF support
author: Martin Holst Swende (@holiman), Marius van der Wijden (@MariusVanDerWijden), Danno Ferrin (@shemnon)
discussions-to: https://ethereum-magicians.org/t/eip-7756-eof-evm-trace-specification/20806
status: Draft
type: Standards Track
category: Interface
created: 2024-08-13
requires: 3155, 4750
---

## Abstract

Updates the [EIP-3155](./eip-3155.md) JSON tracing specification to support EOF features.

## Motivation

EIP-3155 defined a tracing standard for Legacy EVM operations. However, the EVM Object Format ([EIP-7692](./eip-7692.md)) adds a number of features that need to be reflected in debugging traces.

The use of these traces has also moved out from state testing, including live block tracing and differential fuzzing, increasing the need to keep tracing up to date.

This EIP has multiple goals:

- Add members to the trace object to support new EOF features.
- Support tracing contracts contained in an EOF container as well as uncontained "legacy" contracts in the same trace.
- Clarify any previous ambiguities in the EIP-3155 specification.

## Specification

To promote clarity and provide a cohesive specification, the entire tracing specification will be presented with alterations in-line rather than as a set of diffs on top of EIP-3155. Differences will be highlighted in the Backwards Compatibility section.

### Datatypes

| Type | Explanation | JSON member example |
|------------|----------------------------------------------------------------|----------------------------------------|
| Number | JSON number | `"pc":0` |
| Hex-Number | Hex-encoded number | `"gas":"0x2540be400"` |
| String | Plain string | `"opName":"PUSH1"` |
| Hex-String | Hex-encoded string | `"returnData":"0x60616203"` |
| Array | Array of Hex-Strings | `"stack":["0x0", "0x0"]` |
| Key-Value | Key-Value structure with key and values encoded as hex strings | `"storage":{"0x0":"0x1", "0x1":"0x1"}` |
| Boolean | Json bool can either be true or false | `"pass": true` |

### Output

- The client outputs one JSON object per EVM operation executed.
- The client MUST NOT output multiple lines for the same operation execution.
- The client MUST NOT output a line for the `STOP` operation if an error occurred, or if the contract runs out of instructions.

Each object contains the following members.

| Name | Type | Required | Explanation |
|------------------|------------|-----------------|-----------------------------------------------------------|
| `pc` | Number | Yes | Program Counter |
| `section` | Number | Yes if EOF | EOF Code Section |
| `op` | Number | Yes | Opcode |
| `immediate` | Hex-String | *see below* | Immediate argument of the Opcode |
| `gas` | Hex-Number | Yes | Gas left before executing this operation |
| `gasCost` | Hex-Number | Yes | Gas cost of this operation |
| `memory` | Array | No | Array of all allocated values |
| `memSize` | Number | Yes | Size of memory array |
| `stack` | Array | Yes | Array of all values on the stack |
| `depth` | Number | Yes | Depth of the contract call stack (non-CALLF) |
| `functionDepth` | Number | Yes if not zero | Depth of the [EIP-4750](./eip-4750.md) CALLF return stack |
| `returnData` | Hex-String | No | Data returned by contract calls |
| `refund` | Hex-Number | Yes | Amount of **global** gas refunded |
| `opName` | String | No | Name of the operation |
| `error` | Hex-String | No | Description of an error or revert data |
| `storage` | Map | No | Array of all stored values |


- The `pc` value is zero indexed either from the beginning of the contract when the contract is not in an EOF container, or from the beginning of the code section when it is a contract contained in an EOF container.
- The `section` member must only be present when tracing a contract that is contained in an EOF container.
In cases where legacy and EOF contracts are in the same call trace the presence and absence of the `section` member indicates if the contract at that step is EOF or legacy.
- The `immediate` member is optional for PUSH series instructions, and mandatory for all other operations that have immediate arguments.
- For RJUMPV this would include the table length and the entire table. Clients MAY instead store just the table length.
- The `gas`, `stack`, `memory` and `memSize`, `depth`, and `functionDepth` members are the values *before* execution of the op.
- The `gasCost` is the sum of all gas costs, including dynamic costs such as memory expansion, call stipend, and account warming costs.
- All array attributes (`stack`, `memory`) MUST be initialized to empty arrays ("stack":[]` NOT `"stack":null`).
- The `memory` or `storage` members may be omitted if they are empty or the client does not produce them.
- The `memSize` member MUST be present regardless of `memory` support. Even when `memSize` is zero.
- The `functionDepth` member may be omitted when zero. It must be omitted if the contract is legacy EVM.
- The `error` and `returnData` members can be omitted if they are empty.
- If the prior operation failed with an exceptional halt, `error` should identify the halt. Otherwise, if the prior operation was a `REVERT` operation `error` should contain the hex-encoded revert data.
- The `storage` member should only include items read or written via `SSTORE` or `SLOAD`, and not the account's entire storage.
- Clients SHOULD implement a way to disable recording the storage as the stateroot includes all storage updates.
- Clients SHOULD output the members in the same order as listed in this EIP.

*Example:*

```
{"pc":0,"op":96,"gas":"0x2540be400","gasCost":"0x3","memory":"0x","memSize":0,"stack":[],"depth":1,"error":null,"opName":"PUSH1"}
```

### Summary Line

At the end of execution, the client should print summary info. This summary MUST be a single JSON object.

This info SHOULD have the following members.

| Name | Type | Required | Explanation |
|-------------|------------|----------|--------------------------------------------------------|
| `stateRoot` | Hex-String | Yes | Root of the state trie after executing the transaction |
| `output` | Hex-String | Yes | Return values of the function |
| `gasUsed` | Hex-Number | Yes | All gas used by the transaction |
| `pass` | Boolean | Yes | If the tx was successful, or if the test passed |
| `time` | Number | No | Time in nanoseconds needed to execute the transaction |
| `fork` | String | No | Name of the fork rules used for execution |

*Example*:

```
{"stateRoot":"0xd4c577737f5d20207d338c360c42d3af78de54812720e3339f7b27293ef195b7","output":"","gasUsed":"0x3","pass":"true","time":141485}
```

## Rationale

This EIP is an extension of the EIP-3155 tracing features that has been in use for years. Rather than dramatically re-boot the feature, the information was added to the existing traces.

A "mini" trace was contemplated to allow for tracing to be included in tools such as `t8n` and to allow for more efficient RPC tracing calls, but that seemed sufficiently different that it would be a stand-alone EIP rather than an EIP that adds features to the existing tracing capabilities.

The idea of moving to a JSON Schema was rejected to ensure maximum compatibility with existing clients.

## Backwards Compatibility

Clients emitting tracing JSON for uncontained "legacy" contracts will produce a compatible trace, except as outlined below

### Changes from EIP-3155

- The term Client Under Test or CUT has been replaced simply with "client."

### Additions to EIP-3155

- The `immediate` member was added to support the large number of instructions that contain immediate operations.
Without this change, users would need bytes of the contracts being executed to rationalize the traces.
- The `section` and `functionDepth` members were added to support [EIP-4750](./eip-4750) EOF Functions.
- Added clarification around where `pc` indexes when run in an EOF container.

### Clients

Besu, evmone, EthereumJS, Geth, Nethermind, and Reth already produce these standard traces in various tools. Adding the new fields will align with work needed to support the EOF EIPs enumerated in EIP-7692.

## Test Cases

This is the trace output from the Ethereum Execution Specification Test from one of the parameterized executions of [test_eof_functions_contract_call_succeed](https://github.com/ethereum/execution-spec-tests/blob/632d151ea8a71d09a3a0acbdb85d97fa18c8456b/tests/prague/eip7692_eof_v1/eip3540_eof_v1/test_execution_function.py#L304-L335).
Memory and return data is disabled.

```json lines
{"pc":0,"op":96,"gas":"0x2fa9e78","gasCost":"0x3","memSize":0,"stack":[],"depth":1,"refund":0,"opName":"PUSH1"}
{"pc":2,"op":96,"gas":"0x2fa9e75","gasCost":"0x3","memSize":0,"stack":["0x0"],"depth":1,"refund":0,"opName":"PUSH1"}
{"pc":4,"op":96,"gas":"0x2fa9e72","gasCost":"0x3","memSize":0,"stack":["0x0","0x0"],"depth":1,"refund":0,"opName":"PUSH1"}
{"pc":6,"op":96,"gas":"0x2fa9e6f","gasCost":"0x3","memSize":0,"stack":["0x0","0x0","0x0"],"depth":1,"refund":0,"opName":"PUSH1"}
{"pc":8,"op":96,"gas":"0x2fa9e6c","gasCost":"0x3","memSize":0,"stack":["0x0","0x0","0x0","0x0"],"depth":1,"refund":0,"opName":"PUSH1"}
{"pc":10,"op":97,"gas":"0x2fa9e69","gasCost":"0x3","memSize":0,"stack":["0x0","0x0","0x0","0x0","0x0"],"depth":1,"refund":0,"opName":"PUSH2"}
{"pc":13,"op":90,"gas":"0x2fa9e66","gasCost":"0x2","memSize":0,"stack":["0x0","0x0","0x0","0x0","0x0","0x1000"],"depth":1,"refund":0,"opName":"GAS"}
{"pc":14,"op":241,"gas":"0x2fa9e64","gasCost":"0x2eeb414","memSize":0,"stack":["0x0","0x0","0x0","0x0","0x0","0x1000","0x2fa9e64"],"depth":1,"refund":0,"opName":"CALL"}
{"pc":0,"section":0,"op":227,"immediate":"0x0001","gas":"0x2eea9ec","gasCost":"0x5","memSize":0,"stack":[],"depth":2,"refund":0,"opName":"CALLF"}
{"pc":0,"section":1,"op":228,"gas":"0x2eea9e7","gasCost":"0x3","memSize":0,"stack":[],"depth":2,"functionDepth":1,"refund":0,"opName":"RETF"}
{"pc":3,"section":0,"op":0,"gas":"0x2eea9e4","gasCost":"0x0","memSize":0,"stack":[],"depth":2,"refund":0,"opName":"STOP"}
{"pc":15,"op":96,"gas":"0x2fa9434","gasCost":"0x3","memSize":0,"stack":["0x1"],"depth":1,"refund":0,"opName":"PUSH1"}
{"pc":17,"op":85,"gas":"0x2fa9431","gasCost":"0x5654","memSize":0,"stack":["0x1","0x0"],"depth":1,"refund":0,"opName":"SSTORE"}
{"pc":18,"op":0,"gas":"0x2fa3ddd","gasCost":"0x0","memSize":0,"stack":[],"depth":1,"refund":0,"opName":"STOP"}
```

## Security Considerations

Clients should be aware that tracing can be expensive both in terms of CPU overhead and network bandwidth.
Tracing endpoints should not be enabled by default, and when they are enabled should have access restrictions on the network level.
Failure to do so could result in a client being overwhelmed with requests and, if operating as a validator, cause the client to fail to provide execution attestations in a timely manner.

Differential fuzzing is also a double-edged sword.
While it allows client teams the ability to identify consensus splits, the client teams need to be prompt in fixing any issues that are discovered.

## Copyright

Copyright and related rights waived via [CC0](../LICENSE.md).

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