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docs: update tracing docs (#26270)

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* Move JS tracing ref from API page

* add tracerConfig to ref, link to traceConfig in other methods
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  1. 11
      docs/_evm-tracing/builtin-tracers.md
  2. 513
      docs/_evm-tracing/custom-tracer.md
  3. 333
      docs/_evm-tracing/js-tutorial.md
  4. 196
      docs/_rpc/ns-debug.md

11
docs/_evm-tracing/builtin-tracers.md
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@ -210,7 +210,14 @@ Things to note about the call tracer:
- In case a frame reverts, the field `output` will contain the raw return data
- In case the top level frame reverts, its `revertReason` field will contain the parsed reason of revert as returned by the Solidity contract
`callTracer` has an option to only trace the main (top-level) call and none of the sub-calls. This avoids extra processing for each call frame if only the top-level call info are required. Here's how it can be configured:
#### Config
`callTracer` accepts two options:
- `onlyTopCall: true` instructs the tracer to only process the main (top-level) call and none of the sub-calls. This avoids extra processing for each call frame if only the top-level call info are required.
- `withLog: true` instructs the tracer to also collect the logs emitted during each call.
Example invokation with the `onlyTopCall` flag:
```terminal
> debug.traceTransaction('0xc73e70f6d60e63a71dabf90b9983f2cdd56b0cb7bcf1a205f638d630a95bba73', { tracer: 'callTracer', tracerConfig: { onlyTopCall: true } })
@ -504,4 +511,4 @@ debug.traceCall({from: , to: , input: }, 'latest', {stateOverrides: {'0x...': {c
This page showed how to use the tracers that come bundled with Geth. There are a set
written in Go and a set written in Javascript. They are invoked by passing their names
when calling an API method. State overrides can be used in combination with tracers to
examine precisely what the EVM will do in some hypothetical scenario.
examine precisely what the EVM will do in some hypothetical scenario.

513
docs/_evm-tracing/custom-tracer.md
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@ -13,349 +13,6 @@ compiled together with the Geth source code.
* TOC
{:toc}
## Custom Javascript tracing
Transaction traces include the complete status of the EVM at every point during the
transaction execution, which can be a very large amount of data. Often, users are
only interested in a small subset of that data. Javascript trace filters are available
to isolate the useful information. Detailed information about `debug_traceTransaction`
and its component parts is available in the
[reference documentation](/docs/rpc/ns-debug#debug_tracetransaction).
### A simple filter
Filters are Javascript functions that select information from the trace to persist
and discard based on some conditions. The following Javascript function returns
only the sequence of opcodes executed by the transaction as a comma-separated list.
The function could be written directly in the Javascript console, but it is cleaner
to write it in a separate re-usable file and load it into the console.
1. Create a file, `filterTrace_1.js`, with this content:
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'step: function(log,db) {this.retVal.push(log.getPC() + ":" + log.op.toString())},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
2. Run the [JavaScript console](https://geth.ethereum.org/docs/interface/javascript-console).
3. Get the hash of a recent transaction from a node or block explorer.
4. Run this command to run the script:
```javascript
loadScript('filterTrace_1.js');
```
5. Run the tracer from the script. Be patient, it could take a long time.
```javascript
tracer('<hash of transaction>');
```
The bottom of the output looks similar to:
```sh
"3366:POP", "3367:JUMP", "1355:JUMPDEST", "1356:PUSH1", "1358:MLOAD", "1359:DUP1", "1360:DUP3", "1361:ISZERO", "1362:ISZERO",
"1363:ISZERO", "1364:ISZERO", "1365:DUP2", "1366:MSTORE", "1367:PUSH1", "1369:ADD", "1370:SWAP2", "1371:POP", "1372:POP", "1373:PUSH1",
"1375:MLOAD", "1376:DUP1", "1377:SWAP2", "1378:SUB", "1379:SWAP1", "1380:RETURN"
```
6. Run this line to get a more readable output with each string in its own line.
```javascript
console.log(JSON.stringify(tracer('<hash of transaction>'), null, 2));
```
More information about the `JSON.stringify` function is available
[here](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify).
The commands above worked by calling the same `debug.traceTransaction` function that
was previously explained in [basic traces](https://geth.ethereum.org/docs/dapp/tracing),
but with a new parameter, `tracer`. This parameter takes the JavaScript object formated
as a string. In the case of the trace above, it is:
```javascript
{
retVal: [],
step: function(log,db) {this.retVal.push(log.getPC() + ":" + log.op.toString())},
fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},
result: function(ctx,db) {return this.retVal}
}
```
This object has three member functions:
- `step`, called for each opcode.
- `fault`, called if there is a problem in the execution.
- `result`, called to produce the results that are returned by `debug.traceTransaction`
- after the execution is done.
In this case, `retVal` is used to store the list of strings to return in `result`.
The `step` function adds to `retVal` the program counter and the name of the opcode there.
Then, in `result`, this list is returned to be sent to the caller.
### Filtering with conditions
For actual filtered tracing we need an `if` statement to only log relevant information.
For example, to isolate the transaction's interaction with storage, the following tracer
could be used:
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'step: function(log,db) {' +
' if(log.op.toNumber() == 0x54) ' +
' this.retVal.push(log.getPC() + ": SLOAD");' +
' if(log.op.toNumber() == 0x55) ' +
' this.retVal.push(log.getPC() + ": SSTORE");' +
'},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
The `step` function here looks at the opcode number of the op, and only pushes
an entry if the opcode is `SLOAD` or `SSTORE` ([here is a list of EVM opcodes and
their numbers](https://github.com/wolflo/evm-opcodes)). We could have used
`log.op.toString()` instead, but it is faster to compare numbers rather than strings.
The output looks similar to this:
```javascript
[
"5921: SLOAD",
.
.
.
"2413: SSTORE",
"2420: SLOAD",
"2475: SSTORE",
"6094: SSTORE"
]
```
### Stack Information
The trace above reports the program counter (PC) and whether the program read from storage
or wrote to it. That alone isn't particularly useful. To know more, the `log.stack.peek`
function can be used to peek into the stack. `log.stack.peek(0)` is the stack top,
`log.stack.peek(1)` the entry below it, etc.
The values returned by `log.stack.peek` are Go `big.Int` objects. By default they are
converted to JavaScript floating point numbers, so you need `toString(16)` to get them
as hexadecimals, which is how 256-bit values such as storage cells and their content
are normally represented.
#### Storage Information
The function below provides a trace of all the storage operations and their parameters.
This gives a more complete picture of the program's interaction with storage.
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'step: function(log,db) {' +
' if(log.op.toNumber() == 0x54) ' +
' this.retVal.push(log.getPC() + ": SLOAD " + ' +
' log.stack.peek(0).toString(16));' +
' if(log.op.toNumber() == 0x55) ' +
' this.retVal.push(log.getPC() + ": SSTORE " +' +
' log.stack.peek(0).toString(16) + " <- " +' +
' log.stack.peek(1).toString(16));' +
'},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
The output is similar to:
```javascript
[
"5921: SLOAD 0",
.
.
.
"2413: SSTORE 3f0af0a7a3ed17f5ba6a93e0a2a05e766ed67bf82195d2dd15feead3749a575d <- fb8629ad13d9a12456",
"2420: SLOAD cc39b177dd3a7f50d4c09527584048378a692aed24d31d2eabeddb7f3c041870",
"2475: SSTORE cc39b177dd3a7f50d4c09527584048378a692aed24d31d2eabeddb7f3c041870 <- 358c3de691bd19",
"6094: SSTORE 0 <- 1"
]
```
#### Operation Results
One piece of information missing from the function above is the result on an `SLOAD`
operation. The state we get inside `log` is the state prior to the execution of the
opcode, so that value is not known yet. For more operations we can figure it out for
ourselves, but we don't have access to the
storage, so here we can't.
The solution is to have a flag, `afterSload`, which is only true in the opcode right
after an `SLOAD`, when we can see the result at the top of the stack.
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'afterSload: false,' +
'step: function(log,db) {' +
' if(this.afterSload) {' +
' this.retVal.push(" Result: " + ' +
' log.stack.peek(0).toString(16)); ' +
' this.afterSload = false; ' +
' } ' +
' if(log.op.toNumber() == 0x54) {' +
' this.retVal.push(log.getPC() + ": SLOAD " + ' +
' log.stack.peek(0).toString(16));' +
' this.afterSload = true; ' +
' } ' +
' if(log.op.toNumber() == 0x55) ' +
' this.retVal.push(log.getPC() + ": SSTORE " +' +
' log.stack.peek(0).toString(16) + " <- " +' +
' log.stack.peek(1).toString(16));' +
'},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
The output now contains the result in the line that follows the `SLOAD`.
```javascript
[
"5921: SLOAD 0",
" Result: 1",
.
.
.
"2413: SSTORE 3f0af0a7a3ed17f5ba6a93e0a2a05e766ed67bf82195d2dd15feead3749a575d <- fb8629ad13d9a12456",
"2420: SLOAD cc39b177dd3a7f50d4c09527584048378a692aed24d31d2eabeddb7f3c041870",
" Result: 0",
"2475: SSTORE cc39b177dd3a7f50d4c09527584048378a692aed24d31d2eabeddb7f3c041870 <- 358c3de691bd19",
"6094: SSTORE 0 <- 1"
]
```
### Dealing With Calls Between Contracts
So the storage has been treated as if there are only 2<sup>256</sup> cells. However,
that is not true. Contracts can call other contracts, and then the storage involved
is the storage of the other contract. We can see the address of the current contract
in `log.contract.getAddress()`. This value is the execution context - the contract
whose storage we are using - even when code from another contract is executed (by
using
[`CALLCODE` or `DELEGATECALL`](https://docs.soliditylang.org/en/v0.8.14/introduction-to-smart-contracts.html#delegatecall-callcode-and-libraries)).
However, `log.contract.getAddress()` returns an array of bytes. To convert this to
the familiar hexadecimal representation of Ethereum addresses, `this.byteHex()`
and `array2Hex()` can be used.
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'afterSload: false,' +
'callStack: [],' +
'byte2Hex: function(byte) {' +
' if (byte < 0x10) ' +
' return "0" + byte.toString(16); ' +
' return byte.toString(16); ' +
'},' +
'array2Hex: function(arr) {' +
' var retVal = ""; ' +
' for (var i=0; i<arr.length; i++) ' +
' retVal += this.byte2Hex(arr[i]); ' +
' return retVal; ' +
'}, ' +
'getAddr: function(log) {' +
' return this.array2Hex(log.contract.getAddress());' +
'}, ' +
'step: function(log,db) {' +
' var opcode = log.op.toNumber();' +
// SLOAD
' if (opcode == 0x54) {' +
' this.retVal.push(log.getPC() + ": SLOAD " + ' +
' this.getAddr(log) + ":" + ' +
' log.stack.peek(0).toString(16));' +
' this.afterSload = true; ' +
' } ' +
// SLOAD Result
' if (this.afterSload) {' +
' this.retVal.push(" Result: " + ' +
' log.stack.peek(0).toString(16)); ' +
' this.afterSload = false; ' +
' } ' +
// SSTORE
' if (opcode == 0x55) ' +
' this.retVal.push(log.getPC() + ": SSTORE " +' +
' this.getAddr(log) + ":" + ' +
' log.stack.peek(0).toString(16) + " <- " +' +
' log.stack.peek(1).toString(16));' +
// End of step
'},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
The output is similar to:
```javascript
[
"423: SLOAD 22ff293e14f1ec3a09b137e9e06084afd63addf9:360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc",
" Result: 360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc",
"10778: SLOAD 22ff293e14f1ec3a09b137e9e06084afd63addf9:6",
" Result: 6",
.
.
.
"13529: SLOAD f2d68898557ccb2cf4c10c3ef2b034b2a69dad00:8328de571f86baa080836c50543c740196dbc109d42041802573ba9a13efa340",
" Result: 8328de571f86baa080836c50543c740196dbc109d42041802573ba9a13efa340",
"423: SLOAD f2d68898557ccb2cf4c10c3ef2b034b2a69dad00:360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc",
" Result: 360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc",
"13529: SLOAD f2d68898557ccb2cf4c10c3ef2b034b2a69dad00:b38558064d8dd9c883d2a8c80c604667ddb90a324bc70b1bac4e70d90b148ed4",
" Result: b38558064d8dd9c883d2a8c80c604667ddb90a324bc70b1bac4e70d90b148ed4",
"11041: SSTORE 22ff293e14f1ec3a09b137e9e06084afd63addf9:6 <- 0"
]
```
## Other traces
This tutorial has focused on `debug_traceTransaction()` which reports information
about individual transactions. There are also RPC endpoints that provide different
information, including tracing the EVM execution within a block, between two blocks,
for specific `eth_call`s or rejected blocks. The full list of trace functions can
be explored in the [reference documentation](/content/docs/interacting_with_geth/RPC/ns-debug.md).
## Custom Go tracing
Custom tracers can also be made more performant by writing them in Go. The gain in
@ -477,6 +134,174 @@ was registered under:
}
```
## Custom Javascript tracing
Transaction traces include the complete status of the EVM at every point during the
transaction execution, which can be a very large amount of data. Often, users are
only interested in a small subset of that data. Javascript trace filters are available
to isolate the useful information.
Specifying the `tracer` option in one of the tracing methods (see list in [reference](/docs/rpc/ns-debug)) enables JavaScript-based tracing.
In this mode, `tracer` is interpreted as a JavaScript expression that is expected to
evaluate to an object which must expose the `result` and `fault` methods. There exist
4 additional methods, namely: `setup`, `step`, `enter`, and `exit`. `enter` and `exit`
must be present or omitted together.
### Setup
`setup` is invoked once, in the beginning when the tracer is being constructed by Geth
for a given transaction. It takes in one argument `config`. `config` is tracer-specific and
allows users to pass in options to the tracer. `config` is to be JSON-decoded for usage and
its default value is `"{}"`.
The `config` in the following example is the `onlyTopCall` option available in the
`callTracer`:
```js
debug.traceTransaction('<txhash>, { tracer: 'callTracer', tracerConfig: { onlyTopCall: true } })
```
The config in the following example is the `diffMode` option available
in the `prestateTracer`:
```js
debug.traceTransaction('<txhash>, { tracer: 'prestateTracer': tracerConfig: { diffMode: true } })
```
### Step
`step` is a function that takes two arguments, `log` and `db`, and is called for each step
of the EVM, or when an error occurs, as the specified transaction is traced.
`log` has the following fields:
- `op`: Object, an OpCode object representing the current opcode
- `stack`: Object, a structure representing the EVM execution stack
- `memory`: Object, a structure representing the contract's memory space
- `contract`: Object, an object representing the account executing the current operation
and the following methods:
- `getPC()` - returns a Number with the current program counter
- `getGas()` - returns a Number with the amount of gas remaining
- `getCost()` - returns the cost of the opcode as a Number
- `getDepth()` - returns the execution depth as a Number
- `getRefund()` - returns the amount to be refunded as a Number
- `getError()` - returns information about the error if one occured, otherwise returns `undefined`
If error is non-empty, all other fields should be ignored.
For efficiency, the same `log` object is reused on each execution step, updated with current values; make sure to copy values you want to preserve beyond the current call. For instance, this step function will not work:
function(log) {
this.logs.append(log);
}
But this step function will:
function(log) {
this.logs.append({gas: log.getGas(), pc: log.getPC(), ...});
}
`log.op` has the following methods:
- `isPush()` - returns true if the opcode is a PUSHn
- `toString()` - returns the string representation of the opcode
- `toNumber()` - returns the opcode's number
`log.memory` has the following methods:
- `slice(start, stop)` - returns the specified segment of memory as a byte slice
- `getUint(offset)` - returns the 32 bytes at the given offset
- `length()` - returns the memory size
`log.stack` has the following methods:
- `peek(idx)` - returns the idx-th element from the top of the stack (0 is the topmost element) as a big.Int
- `length()` - returns the number of elements in the stack
`log.contract` has the following methods:
- `getCaller()` - returns the address of the caller
- `getAddress()` - returns the address of the current contract
- `getValue()` - returns the amount of value sent from caller to contract as a big.Int
- `getInput()` - returns the input data passed to the contract
`db` has the following methods:
- `getBalance(address)` - returns a `big.Int` with the specified account's balance
- `getNonce(address)` - returns a Number with the specified account's nonce
- `getCode(address)` - returns a byte slice with the code for the specified account
- `getState(address, hash)` - returns the state value for the specified account and the specified hash
- `exists(address)` - returns true if the specified address exists
If the step function throws an exception or executes an illegal operation at any point, it will not be called on any further VM steps, and the error will be returned to the caller.
### Result
`result` is a function that takes two arguments `ctx` and `db`, and is expected to return a JSON-serializable value to return to the RPC caller.
`ctx` is the context in which the transaction is executing and has the following fields:
- `type` - String, one of the two values `CALL` and `CREATE`
- `from` - Address, sender of the transaction
- `to` - Address, target of the transaction
- `input` - Buffer, input transaction data
- `gas` - Number, gas budget of the transaction
- `gasUsed` - Number, amount of gas used in executing the transaction (excludes txdata costs)
- `gasPrice` - Number, gas price configured in the transaction being executed
- `intrinsicGas` - Number, intrinsic gas for the transaction being executed
- `value` - big.Int, amount to be transferred in wei
- `block` - Number, block number
- `output` - Buffer, value returned from EVM
- `time` - String, execution runtime
And these fields are only available for tracing mined transactions (i.e. not available when doing `debug_traceCall`):
- `blockHash` - Buffer, hash of the block that holds the transaction being executed
- `txIndex` - Number, index of the transaction being executed in the block
- `txHash` - Buffer, hash of the transaction being executed
### Fault
`fault` is a function that takes two arguments, `log` and `db`, just like `step` and is invoked when an error happens during the execution of an opcode which wasn't reported in `step`. The method `log.getError()` has information about the error.
### Enter & Exit
`enter` and `exit` are respectively invoked on stepping in and out of an internal call. More specifically they are invoked on the `CALL` variants, `CREATE` variants and also for the transfer implied by a `SELFDESTRUCT`.
`enter` takes a `callFrame` object as argument which has the following methods:
- `getType()` - returns a string which has the type of the call frame
- `getFrom()` - returns the address of the call frame sender
- `getTo()` - returns the address of the call frame target
- `getInput()` - returns the input as a buffer
- `getGas()` - returns a Number which has the amount of gas provided for the frame
- `getValue()` - returns a `big.Int` with the amount to be transferred only if available, otherwise `undefined`
`exit` takes in a `frameResult` object which has the following methods:
- `getGasUsed()` - returns amount of gas used throughout the frame as a Number
- `getOutput()` - returns the output as a buffer
` -getError()` - returns an error if one occured during execution and `undefined` otherwise
### Usage
Note that several values are Golang big.Int objects, not JavaScript numbers or JS bigints. As such, they have the same interface as described in the godocs. Their default serialization to JSON is as a Javascript number; to serialize large numbers accurately call `.String()` on them. For convenience, `big.NewInt(x)` is provided, and will convert a uint to a Go BigInt.
Usage example, returns the top element of the stack at each CALL opcode only:
debug.traceTransaction(txhash, {tracer: '{data: [], fault: function(log) {}, step: function(log) { if(log.op.toString() == "CALL") this.data.push(log.stack.peek(0)); }, result: function() { return this.data; }}'});
## Other traces
This tutorial has focused on `debug_traceTransaction()` which reports information
about individual transactions. There are also RPC endpoints that provide different
information, including tracing the EVM execution within a block, between two blocks,
for specific `eth_call`s or rejected blocks. The full list of trace functions can
be explored in the [reference documentation](/content/docs/interacting_with_geth/RPC/ns-debug.md).
## Summary
This page described how to write custom tracers for Geth. Custom tracers can be written in Javascript or Go.
This page described how to write custom tracers for Geth. Custom tracers can be written in Javascript or Go.

333
docs/_evm-tracing/js-tutorial.md
Unescape View File

@ -0,0 +1,333 @@
---
title: Tutorial for Javascript tracing
sort_key: E
---
Geth supports tracing via [custom Javascript tracers](/docs/evm-tracing/custom-tracer#custom-javascript-tracing). This document provides a tutorial with examples
on how to achieve this.
### A simple filter
Filters are Javascript functions that select information from the trace to persist
and discard based on some conditions. The following Javascript function returns
only the sequence of opcodes executed by the transaction as a comma-separated list.
The function could be written directly in the Javascript console, but it is cleaner
to write it in a separate re-usable file and load it into the console.
1. Create a file, `filterTrace_1.js`, with this content:
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'step: function(log,db) {this.retVal.push(log.getPC() + ":" + log.op.toString())},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
2. Run the [JavaScript console](https://geth.ethereum.org/docs/interface/javascript-console).
3. Get the hash of a recent transaction from a node or block explorer.
4. Run this command to run the script:
```javascript
loadScript('filterTrace_1.js');
```
5. Run the tracer from the script. Be patient, it could take a long time.
```javascript
tracer('<hash of transaction>');
```
The bottom of the output looks similar to:
```sh
"3366:POP", "3367:JUMP", "1355:JUMPDEST", "1356:PUSH1", "1358:MLOAD", "1359:DUP1", "1360:DUP3", "1361:ISZERO", "1362:ISZERO",
"1363:ISZERO", "1364:ISZERO", "1365:DUP2", "1366:MSTORE", "1367:PUSH1", "1369:ADD", "1370:SWAP2", "1371:POP", "1372:POP", "1373:PUSH1",
"1375:MLOAD", "1376:DUP1", "1377:SWAP2", "1378:SUB", "1379:SWAP1", "1380:RETURN"
```
6. Run this line to get a more readable output with each string in its own line.
```javascript
console.log(JSON.stringify(tracer('<hash of transaction>'), null, 2));
```
More information about the `JSON.stringify` function is available
[here](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify).
The commands above worked by calling the same `debug.traceTransaction` function that
was previously explained in [basic traces](https://geth.ethereum.org/docs/dapp/tracing),
but with a new parameter, `tracer`. This parameter takes the JavaScript object formated
as a string. In the case of the trace above, it is:
```javascript
{
retVal: [],
step: function(log,db) {this.retVal.push(log.getPC() + ":" + log.op.toString())},
fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},
result: function(ctx,db) {return this.retVal}
}
```
This object has three member functions:
- `step`, called for each opcode.
- `fault`, called if there is a problem in the execution.
- `result`, called to produce the results that are returned by `debug.traceTransaction`
- after the execution is done.
In this case, `retVal` is used to store the list of strings to return in `result`.
The `step` function adds to `retVal` the program counter and the name of the opcode there.
Then, in `result`, this list is returned to be sent to the caller.
### Filtering with conditions
For actual filtered tracing we need an `if` statement to only log relevant information.
For example, to isolate the transaction's interaction with storage, the following tracer
could be used:
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'step: function(log,db) {' +
' if(log.op.toNumber() == 0x54) ' +
' this.retVal.push(log.getPC() + ": SLOAD");' +
' if(log.op.toNumber() == 0x55) ' +
' this.retVal.push(log.getPC() + ": SSTORE");' +
'},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
The `step` function here looks at the opcode number of the op, and only pushes
an entry if the opcode is `SLOAD` or `SSTORE` ([here is a list of EVM opcodes and
their numbers](https://github.com/wolflo/evm-opcodes)). We could have used
`log.op.toString()` instead, but it is faster to compare numbers rather than strings.
The output looks similar to this:
```javascript
[
"5921: SLOAD",
.
.
.
"2413: SSTORE",
"2420: SLOAD",
"2475: SSTORE",
"6094: SSTORE"
]
```
### Stack Information
The trace above reports the program counter (PC) and whether the program read from storage
or wrote to it. That alone isn't particularly useful. To know more, the `log.stack.peek`
function can be used to peek into the stack. `log.stack.peek(0)` is the stack top,
`log.stack.peek(1)` the entry below it, etc.
The values returned by `log.stack.peek` are Go `big.Int` objects. By default they are
converted to JavaScript floating point numbers, so you need `toString(16)` to get them
as hexadecimals, which is how 256-bit values such as storage cells and their content
are normally represented.
#### Storage Information
The function below provides a trace of all the storage operations and their parameters.
This gives a more complete picture of the program's interaction with storage.
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'step: function(log,db) {' +
' if(log.op.toNumber() == 0x54) ' +
' this.retVal.push(log.getPC() + ": SLOAD " + ' +
' log.stack.peek(0).toString(16));' +
' if(log.op.toNumber() == 0x55) ' +
' this.retVal.push(log.getPC() + ": SSTORE " +' +
' log.stack.peek(0).toString(16) + " <- " +' +
' log.stack.peek(1).toString(16));' +
'},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
The output is similar to:
```javascript
[
"5921: SLOAD 0",
.
.
.
"2413: SSTORE 3f0af0a7a3ed17f5ba6a93e0a2a05e766ed67bf82195d2dd15feead3749a575d <- fb8629ad13d9a12456",
"2420: SLOAD cc39b177dd3a7f50d4c09527584048378a692aed24d31d2eabeddb7f3c041870",
"2475: SSTORE cc39b177dd3a7f50d4c09527584048378a692aed24d31d2eabeddb7f3c041870 <- 358c3de691bd19",
"6094: SSTORE 0 <- 1"
]
```
#### Operation Results
One piece of information missing from the function above is the result on an `SLOAD`
operation. The state we get inside `log` is the state prior to the execution of the
opcode, so that value is not known yet. For more operations we can figure it out for
ourselves, but we don't have access to the
storage, so here we can't.
The solution is to have a flag, `afterSload`, which is only true in the opcode right
after an `SLOAD`, when we can see the result at the top of the stack.
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'afterSload: false,' +
'step: function(log,db) {' +
' if(this.afterSload) {' +
' this.retVal.push(" Result: " + ' +
' log.stack.peek(0).toString(16)); ' +
' this.afterSload = false; ' +
' } ' +
' if(log.op.toNumber() == 0x54) {' +
' this.retVal.push(log.getPC() + ": SLOAD " + ' +
' log.stack.peek(0).toString(16));' +
' this.afterSload = true; ' +
' } ' +
' if(log.op.toNumber() == 0x55) ' +
' this.retVal.push(log.getPC() + ": SSTORE " +' +
' log.stack.peek(0).toString(16) + " <- " +' +
' log.stack.peek(1).toString(16));' +
'},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
The output now contains the result in the line that follows the `SLOAD`.
```javascript
[
"5921: SLOAD 0",
" Result: 1",
.
.
.
"2413: SSTORE 3f0af0a7a3ed17f5ba6a93e0a2a05e766ed67bf82195d2dd15feead3749a575d <- fb8629ad13d9a12456",
"2420: SLOAD cc39b177dd3a7f50d4c09527584048378a692aed24d31d2eabeddb7f3c041870",
" Result: 0",
"2475: SSTORE cc39b177dd3a7f50d4c09527584048378a692aed24d31d2eabeddb7f3c041870 <- 358c3de691bd19",
"6094: SSTORE 0 <- 1"
]
```
### Dealing With Calls Between Contracts
So the storage has been treated as if there are only 2<sup>256</sup> cells. However,
that is not true. Contracts can call other contracts, and then the storage involved
is the storage of the other contract. We can see the address of the current contract
in `log.contract.getAddress()`. This value is the execution context - the contract
whose storage we are using - even when code from another contract is executed (by
using
[`CALLCODE` or `DELEGATECALL`](https://docs.soliditylang.org/en/v0.8.14/introduction-to-smart-contracts.html#delegatecall-callcode-and-libraries)).
However, `log.contract.getAddress()` returns an array of bytes. To convert this to
the familiar hexadecimal representation of Ethereum addresses, `this.byteHex()`
and `array2Hex()` can be used.
```javascript
tracer = function (tx) {
return debug.traceTransaction(tx, {
tracer:
'{' +
'retVal: [],' +
'afterSload: false,' +
'callStack: [],' +
'byte2Hex: function(byte) {' +
' if (byte < 0x10) ' +
' return "0" + byte.toString(16); ' +
' return byte.toString(16); ' +
'},' +
'array2Hex: function(arr) {' +
' var retVal = ""; ' +
' for (var i=0; i<arr.length; i++) ' +
' retVal += this.byte2Hex(arr[i]); ' +
' return retVal; ' +
'}, ' +
'getAddr: function(log) {' +
' return this.array2Hex(log.contract.getAddress());' +
'}, ' +
'step: function(log,db) {' +
' var opcode = log.op.toNumber();' +
// SLOAD
' if (opcode == 0x54) {' +
' this.retVal.push(log.getPC() + ": SLOAD " + ' +
' this.getAddr(log) + ":" + ' +
' log.stack.peek(0).toString(16));' +
' this.afterSload = true; ' +
' } ' +
// SLOAD Result
' if (this.afterSload) {' +
' this.retVal.push(" Result: " + ' +
' log.stack.peek(0).toString(16)); ' +
' this.afterSload = false; ' +
' } ' +
// SSTORE
' if (opcode == 0x55) ' +
' this.retVal.push(log.getPC() + ": SSTORE " +' +
' this.getAddr(log) + ":" + ' +
' log.stack.peek(0).toString(16) + " <- " +' +
' log.stack.peek(1).toString(16));' +
// End of step
'},' +
'fault: function(log,db) {this.retVal.push("FAULT: " + JSON.stringify(log))},' +
'result: function(ctx,db) {return this.retVal}' +
'}'
}); // return debug.traceTransaction ...
}; // tracer = function ...
```
The output is similar to:
```javascript
[
"423: SLOAD 22ff293e14f1ec3a09b137e9e06084afd63addf9:360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc",
" Result: 360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc",
"10778: SLOAD 22ff293e14f1ec3a09b137e9e06084afd63addf9:6",
" Result: 6",
.
.
.
"13529: SLOAD f2d68898557ccb2cf4c10c3ef2b034b2a69dad00:8328de571f86baa080836c50543c740196dbc109d42041802573ba9a13efa340",
" Result: 8328de571f86baa080836c50543c740196dbc109d42041802573ba9a13efa340",
"423: SLOAD f2d68898557ccb2cf4c10c3ef2b034b2a69dad00:360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc",
" Result: 360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc",
"13529: SLOAD f2d68898557ccb2cf4c10c3ef2b034b2a69dad00:b38558064d8dd9c883d2a8c80c604667ddb90a324bc70b1bac4e70d90b148ed4",
" Result: b38558064d8dd9c883d2a8c80c604667ddb90a324bc70b1bac4e70d90b148ed4",
"11041: SSTORE 22ff293e14f1ec3a09b137e9e06084afd63addf9:6 <- 0"
]
```

196
docs/_rpc/ns-debug.md
Unescape View File

@ -499,6 +499,7 @@ Returns the storage at the given block height and transaction index. The result
### debug_traceBadBlock
Returns the structured logs created during the execution of EVM against a block pulled from the pool of bad ones and returns them as a JSON object.
For the second parameter see [TraceConfig](#traceconfig) reference.
| Client | Method invocation |
| :------ | -------------------------------------------------------------- |
@ -509,11 +510,11 @@ Returns the structured logs created during the execution of EVM against a block
The `traceBlock` method will return a full stack trace of all invoked opcodes of all transaction
that were included in this block. **Note**, the parent of this block must be present or it will
fail.
fail. For the second parameter see [TraceConfig](#traceconfig) reference.
| Client | Method invocation |
| :------ | ------------------------------------------------------------------------ |
| Go | `debug.TraceBlock(blockRlp []byte, config. *vm.Config) BlockTraceResult` |
| Go | `debug.TraceBlock(blockRlp []byte, config *TraceConfig) BlockTraceResult` |
| Console | `debug.traceBlock(tblockRlp, [options])` |
| RPC | `{"method": "debug_traceBlock", "params": [blockRlp, {}]}` |
@ -559,11 +560,11 @@ References:
### debug_traceBlockByNumber
Similar to [debug_traceBlock](#debug_traceblock), `traceBlockByNumber` accepts a block number and will replay the
block that is already present in the database.
block that is already present in the database. For the second parameter see [TraceConfig](#traceconfig) reference.
| Client | Method invocation |
| :------ | ------------------------------------------------------------------------------ |
| Go | `debug.TraceBlockByNumber(number uint64, config. *vm.Config) BlockTraceResult` |
| Go | `debug.TraceBlockByNumber(number uint64, config *TraceConfig) BlockTraceResult` |
| Console | `debug.traceBlockByNumber(number, [options])` |
| RPC | `{"method": "debug_traceBlockByNumber", "params": [number, {}]}` |
@ -573,11 +574,11 @@ References:
### debug_traceBlockByHash
Similar to [debug_traceBlock](#debug_traceblock), `traceBlockByHash` accepts a block hash and will replay the
block that is already present in the database.
block that is already present in the database. For the second parameter see [TraceConfig](#traceconfig) reference.
| Client | Method invocation |
| :------ | ------------------------------------------------------------------------------- |
| Go | `debug.TraceBlockByHash(hash common.Hash, config. *vm.Config) BlockTraceResult` |
| Go | `debug.TraceBlockByHash(hash common.Hash, config *TraceConfig) BlockTraceResult` |
| Console | `debug.traceBlockByHash(hash, [options])` |
| RPC | `{"method": "debug_traceBlockByHash", "params": [hash {}]}` |
@ -588,10 +589,11 @@ References:
### debug_traceBlockFromFile
Similar to [debug_traceBlock](#debug_traceblock), `traceBlockFromFile` accepts a file containing the RLP of the block.
For the second parameter see [TraceConfig](#traceconfig) reference.
| Client | Method invocation |
| :------ | -------------------------------------------------------------------------------- |
| Go | `debug.TraceBlockFromFile(fileName string, config. *vm.Config) BlockTraceResult` |
| Go | `debug.TraceBlockFromFile(fileName string, config *TraceConfig) BlockTraceResult` |
| Console | `debug.traceBlockFromFile(fileName, [options])` |
| RPC | `{"method": "debug_traceBlockFromFile", "params": [fileName, {}]}` |
@ -600,7 +602,7 @@ References:
### debug_traceCall
The `debug_traceCall` method lets you run an `eth_call` within the context of the given block execution using the final state of parent block as the base. The first argument (just as in `eth_call`) is a [transaction object](/docs/rpc/objects#transaction-call-object). The block can be specified either by hash or by number as the second argument. A tracer can be specified as a third argument, similar to `debug_traceTransaction`. It returns the same output as `debug_traceTransaction`.
The `debug_traceCall` method lets you run an `eth_call` within the context of the given block execution using the final state of parent block as the base. The first argument (just as in `eth_call`) is a [transaction object](/docs/rpc/objects#transaction-call-object). The block can be specified either by hash or by number as the second argument. The trace can be configured similar to `debug_traceTransaction`, see [TraceConfig](#traceconfig). The method returns the same output as `debug_traceTransaction`.
| Client | Method invocation |
| :-----: | --------------------------------------------------------------------------------------------------------------------------- |
@ -691,6 +693,15 @@ as it was executed on the network. It will replay any transaction that may have
to this one before it will finally attempt to execute the transaction that corresponds to the given
hash.
| Client | Method invocation |
| :------ | -------------------------------------------------------------------------------------------- |
| Go | `debug.TraceTransaction(txHash common.Hash, config *TraceConfig) (*ExecutionResult, error)` |
| Console | `debug.traceTransaction(txHash, [options])` |
| RPC | `{"method": "debug_traceTransaction", "params": [txHash, {}]}` |
#### TraceConfig
In addition to the hash of the transaction you may give it a secondary *optional* argument, which
specifies the options for this specific call. The possible options are:
@ -698,16 +709,17 @@ specifies the options for this specific call. The possible options are:
* `disableStack`: `BOOL`. Setting this to true will disable stack capture (default = false).
* `enableMemory`: `BOOL`. Setting this to true will enable memory capture (default = false).
* `enableReturnData`: `BOOL`. Setting this to true will enable return data capture (default = false).
* `tracer`: `STRING`. Setting this will enable JavaScript-based transaction tracing, described below.
* `tracer`: `STRING`. Name for built-in tracer or Javascript expression. See below for more details.
If set, the previous four arguments will be ignored.
If set, the previous four arguments will be ignored.
* `timeout`: `STRING`. Overrides the default timeout of 5 seconds for JavaScript-based tracing calls.
Valid values are described [here](https://golang.org/pkg/time/#ParseDuration).
* `tracerConfig`: Config for the specified `tracer`. For example see callTracer's [config](/docs/evm-tracing/builtin-tracers#config).
| Client | Method invocation |
| :------ | -------------------------------------------------------------------------------------------- |
| Go | `debug.TraceTransaction(txHash common.Hash, logger *vm.LogConfig) (*ExecutionResult, error)` |
| Console | `debug.traceTransaction(txHash, [options])` |
| RPC | `{"method": "debug_traceTransaction", "params": [txHash, {}]}` |
Geth comes with a bundle of [built-in tracers](/docs/evm-tracing/builtin-tracers), each providing various data about a transaction.
This method defaults to the [struct logger](/docs/evm-tracing/builtin-tracers#structopcode-logger). The `tracer` field of
the second parameter can be set to use any of the other tracers. Alternatively a [custom tracer](/docs/evm-tracing/custom-tracer) can be implemented
in either Go or Javascript.
#### Example
@ -745,162 +757,6 @@ specifies the options for this specific call. The possible options are:
}]
```
#### JavaScript-based tracing
Specifying the `tracer` option in the second argument enables JavaScript-based tracing.
In this mode, `tracer` is interpreted as a JavaScript expression that is expected to
evaluate to an object which must expose the `result` and `fault` methods. There exist
4 additional methods, namely: `setup`, `step`, `enter`, and `exit`. `enter` and `exit`
must be present or omitted together.
##### Setup
`setup` is invoked once, in the beginning when the tracer is being constructed by Geth
for a given transaction. It takes in one argument `config`. `config` is tracer-specific and
allows users to pass in options to the tracer. `config` is to be JSON-decoded for usage and
its default value is `"{}"`.
The `config` in the following example is the `onlyTopCall` option available in the
`callTracer`:
```js
debug.traceTransaction('<txhash>, { tracer: 'callTracer', tracerConfig: { onlyTopCall: true } })
```
The config in the following example is the `diffMode` option available
in the `prestateTracer`:
```js
debug.traceTransaction('<txhash>, { tracer: 'prestateTracer': tracerConfig: { diffMode: true } })
```
##### Step
`step` is a function that takes two arguments, `log` and `db`, and is called for each step
of the EVM, or when an error occurs, as the specified transaction is traced.
`log` has the following fields:
- `op`: Object, an OpCode object representing the current opcode
- `stack`: Object, a structure representing the EVM execution stack
- `memory`: Object, a structure representing the contract's memory space
- `contract`: Object, an object representing the account executing the current operation
and the following methods:
- `getPC()` - returns a Number with the current program counter
- `getGas()` - returns a Number with the amount of gas remaining
- `getCost()` - returns the cost of the opcode as a Number
- `getDepth()` - returns the execution depth as a Number
- `getRefund()` - returns the amount to be refunded as a Number
- `getError()` - returns information about the error if one occured, otherwise returns `undefined`
If error is non-empty, all other fields should be ignored.
For efficiency, the same `log` object is reused on each execution step, updated with current values; make sure to copy values you want to preserve beyond the current call. For instance, this step function will not work:
function(log) {
this.logs.append(log);
}
But this step function will:
function(log) {
this.logs.append({gas: log.getGas(), pc: log.getPC(), ...});
}
`log.op` has the following methods:
- `isPush()` - returns true if the opcode is a PUSHn
- `toString()` - returns the string representation of the opcode
- `toNumber()` - returns the opcode's number
`log.memory` has the following methods:
- `slice(start, stop)` - returns the specified segment of memory as a byte slice
- `getUint(offset)` - returns the 32 bytes at the given offset
- `length()` - returns the memory size
`log.stack` has the following methods:
- `peek(idx)` - returns the idx-th element from the top of the stack (0 is the topmost element) as a big.Int
- `length()` - returns the number of elements in the stack
`log.contract` has the following methods:
- `getCaller()` - returns the address of the caller
- `getAddress()` - returns the address of the current contract
- `getValue()` - returns the amount of value sent from caller to contract as a big.Int
- `getInput()` - returns the input data passed to the contract
`db` has the following methods:
- `getBalance(address)` - returns a `big.Int` with the specified account's balance
- `getNonce(address)` - returns a Number with the specified account's nonce
- `getCode(address)` - returns a byte slice with the code for the specified account
- `getState(address, hash)` - returns the state value for the specified account and the specified hash
- `exists(address)` - returns true if the specified address exists
If the step function throws an exception or executes an illegal operation at any point, it will not be called on any further VM steps, and the error will be returned to the caller.
##### Result
`result` is a function that takes two arguments `ctx` and `db`, and is expected to return a JSON-serializable value to return to the RPC caller.
`ctx` is the context in which the transaction is executing and has the following fields:
- `type` - String, one of the two values `CALL` and `CREATE`
- `from` - Address, sender of the transaction
- `to` - Address, target of the transaction
- `input` - Buffer, input transaction data
- `gas` - Number, gas budget of the transaction
- `gasUsed` - Number, amount of gas used in executing the transaction (excludes txdata costs)
- `gasPrice` - Number, gas price configured in the transaction being executed
- `intrinsicGas` - Number, intrinsic gas for the transaction being executed
- `value` - big.Int, amount to be transferred in wei
- `block` - Number, block number
- `output` - Buffer, value returned from EVM
- `time` - String, execution runtime
And these fields are only available for tracing mined transactions (i.e. not available when doing `debug_traceCall`):
- `blockHash` - Buffer, hash of the block that holds the transaction being executed
- `txIndex` - Number, index of the transaction being executed in the block
- `txHash` - Buffer, hash of the transaction being executed
##### Fault
`fault` is a function that takes two arguments, `log` and `db`, just like `step` and is invoked when an error happens during the execution of an opcode which wasn't reported in `step`. The method `log.getError()` has information about the error.
##### Enter & Exit
`enter` and `exit` are respectively invoked on stepping in and out of an internal call. More specifically they are invoked on the `CALL` variants, `CREATE` variants and also for the transfer implied by a `SELFDESTRUCT`.
`enter` takes a `callFrame` object as argument which has the following methods:
- `getType()` - returns a string which has the type of the call frame
- `getFrom()` - returns the address of the call frame sender
- `getTo()` - returns the address of the call frame target
- `getInput()` - returns the input as a buffer
- `getGas()` - returns a Number which has the amount of gas provided for the frame
- `getValue()` - returns a `big.Int` with the amount to be transferred only if available, otherwise `undefined`
`exit` takes in a `frameResult` object which has the following methods:
- `getGasUsed()` - returns amount of gas used throughout the frame as a Number
- `getOutput()` - returns the output as a buffer
` -getError()` - returns an error if one occured during execution and `undefined` otherwise
##### Usage
Note that several values are Golang big.Int objects, not JavaScript numbers or JS bigints. As such, they have the same interface as described in the godocs. Their default serialization to JSON is as a Javascript number; to serialize large numbers accurately call `.String()` on them. For convenience, `big.NewInt(x)` is provided, and will convert a uint to a Go BigInt.
Usage example, returns the top element of the stack at each CALL opcode only:
debug.traceTransaction(txhash, {tracer: '{data: [], fault: function(log) {}, step: function(log) { if(log.op.toString() == "CALL") this.data.push(log.stack.peek(0)); }, result: function() { return this.data; }}'});
### debug_verbosity
Sets the logging verbosity ceiling. Log messages with level

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