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tracer: clarify prestateTracer diff mode behavior (#30912) 

Based on
https://github.com/ethereum/go-ethereum/issues/30774#issuecomment-2504146053

Add more descrption for the `to` field in callTracer, and also refine
the `diffMode` in prestateTracer:
- Clarifies when ALL fields (`nonce`, `balance`, `code`) are included in
the `pre` object
- Adds detail about storage clearing behavior (zero value treatment)

---------

Signed-off-by: jsvisa <delweng@gmail.com>
Co-authored-by: Sina M <1591639+s1na@users.noreply.github.com>
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Delweng 2024-12-16 22:48:43 +08:00 committed by GitHub
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117
docs/developers/evm-tracing/built-in-tracers.md
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@ -59,43 +59,35 @@ Return:
```terminal ```terminal
{ {
"gas":25523, "gas": 25523,
"failed":false, "failed": false,
"returnValue":"", "returnValue": "",
"structLogs":[ "structLogs": [
{ {
"pc":0, "pc": 0,
"op":"PUSH1", "op": "PUSH1",
"gas":64580, "gas": 64580,
"gasCost":3, "gasCost": 3,
"depth":1, "depth": 1,
"error":null, "error": null,
"stack":[ "stack": [ ... ],
"memory": null,
], "storage": { ... }
"memory":null, },
"storage":{ {
"pc": 2,
} "op": "PUSH1",
}, "gas": 64577,
{ "gasCost": 3,
"pc":2, "depth": 1,
"op":"PUSH1", "error": null,
"gas":64577, "stack": [
"gasCost":3, "0000000000000000000000000000000000000000000000000000000000000060"
"depth":1, ],
"error":null, "memory": null,
"stack":[ "storage": { ... }
"0000000000000000000000000000000000000000000000000000000000000060" },
], ...
"memory":null,
"storage":{
}
},
...
``` ```
## Native tracers {#native-tracers} ## Native tracers {#native-tracers}
@ -112,7 +104,7 @@ The `4byteTracer` collects the function selectors of every function executed in
Example call: Example call:
```sh ```sh
debug.traceTransaction( "0x214e597e35da083692f5386141e69f47e973b2c56e7a8073b1ea08fd7571e9de", {tracer: "4byteTracer"}) debug.traceTransaction("0x214e597e35da083692f5386141e69f47e973b2c56e7a8073b1ea08fd7571e9de", {tracer: "4byteTracer"})
``` ```
Return: Return:
@ -131,19 +123,26 @@ Return:
The `callTracer` tracks all the call frames executed during a transaction, including depth 0. The result will be a nested list of call frames, resembling how EVM works. They form a tree with the top-level call at root and sub-calls as children of the higher levels. Each call frame has the following fields: The `callTracer` tracks all the call frames executed during a transaction, including depth 0. The result will be a nested list of call frames, resembling how EVM works. They form a tree with the top-level call at root and sub-calls as children of the higher levels. Each call frame has the following fields:
| field | type | description | | field | type | description |
| ------------ | ----------- | ------------------------------------ | | ------------ | ----------- | -------------------------------------------------------------------------------- |
| type | string | CALL or CREATE | | type | string | the type of call (CALL, STATICCALL, DELEGATECALL, CREATE, CREATE2, SELFDESTRUCT) |
| from | string | address | | from | string | the address initiating the call |
| to | string | address | | to | string | the target address receiving the call |
| value | string | hex-encoded amount of value transfer | | value | string | hex-encoded amount of ETH transfer |
| gas | string | hex-encoded gas provided for call | | gas | string | hex-encoded gas provided for call |
| gasUsed | string | hex-encoded gas used during call | | gasUsed | string | hex-encoded gas used during call |
| input | string | call data | | input | string | call data |
| output | string | return data | | output | string | return data |
| error | string | error, if any | | error | string | error informaction if the call failed |
| revertReason | string | Solidity revert reason, if any | | revertReason | string | Solidity revert reason, if any |
| calls | []callframe | list of sub-calls | | calls | []callframe | list of nested sub-calls |
Hints the `to` address, which varies by call type:
- `CALL/STATICCALL`: The contract or receiving address being called
- `DELEGATECALL`: The contract whose code is being executed
- `CREATE/CREATE2`: The address of the newly deployed contract
- `SELFDESTRUCT/SUICIDE`: The address of the refund recipient
Example Call: Example Call:
@ -222,11 +221,17 @@ The prestate tracer has two modes: `prestate` and `diff`. The `prestate` mode re
In `diff` mode the result object will contain a `pre` and a `post` object: In `diff` mode the result object will contain a `pre` and a `post` object:
1. The result only includes accounts that were modified. Accounts without changes will be omitted in this mode. 1. The result only includes accounts that were modified. Accounts without changes will be omitted in this mode.
2. In `pre` you will find the state of an account before the tx started, and in `post` its state after tx execution finished. 2. The `pre` object within the result captures the account's state at the beginning of the transaction, showcasing its initial values, while the `post` object represents the account's state once the transaction has been fully executed, revealing the outcome of the changes.
3. `pre` can include fields that were not modified, if some other fields for the same account were modified. 3. The accounts in the `pre` object will still contain all of their basic fields—nonce, balance, and code—even if those fields have not been modified. Storage slots, however, are an exception. Only non-empty slots that have been modified will be included. In other words, if a new slot was written to, it will not appear in the `pre` object.
4. `post` will contain only the modified fields. e.g. if `nonce` of an account hasn't changed it will be omitted from `post`. 4. The `post` object is more selective - it only contains the specific fields that were actually modified during the transaction. For example, if only the storage was modified, `post` will not include unchanged fields like `nonce`, `balance`, or `code`.
5. Deletion (i.e. account selfdestruct, or storage clearing) will be signified by inclusion in `pre` and omission in `post`. 5. Deletion operations are represented by:
6. Insertion (i.e. account creation or new slots) will be signified by omission in `pre` and inclusion in `post`.
- Account selfdestruct: Account appears in `pre` but not in `post`
- Storage clearing (setting a storage value to zero is also treated as clearing): Storage slot appears in `pre` but not in `post`
6. Insertion operations are represented by:
- New account creation: Account appears in `post` but not in `pre`
- New storage slot: Storage slot appears in `post` but not in `pre`
To run this tracer in `diff` mode, pass `tracerConfig: {diffMode: true}` in the API call. To run this tracer in `diff` mode, pass `tracerConfig: {diffMode: true}` in the API call.