Fix EVM tracer crash bug when serializing nil stack (#1697)

* Fix EVM tracer crash bug when serializing nil stack

* Fix t8n tracer doc

add following description to reflect new functionality
  `stdout` - into the stdout output.
  `stderr` - into the stderr output.
  <file>   - into the file <file>-<txIndex>.jsonl.
  none     - output.basedir/trace-<txIndex>-<txhash>.jsonl.

nimbus/evm/tracer/json_tracer.nim

@@ -88,6 +88,9 @@ proc captureOpImpl(ctx: JsonTracer, pc: int,
     res["memory"] = mem
 
   if TracerFlags.DisableStack notin ctx.flags:
+    if ctx.stack.isNil:
+      res["stack"] = newJArray()
+    else:
       res["stack"] = ctx.stack
 
   if TracerFlags.DisableReturnData notin ctx.flags:

tools/t8n/config.nim

@@ -28,9 +28,15 @@ type
 
   T8NConf* = object of RootObj
     traceEnabled* {.
-      desc: "Output full trace logs to files trace-<txIndex>-<txhash>.jsonl"
-      defaultValue: false
-      name: "trace" }: bool
+      desc: "Enable and set where to put full EVM trace logs"
+      longDesc:
+        "`stdout` - into the stdout output\n" &
+        "`stderr` - into the stderr output\n" &
+        "<file>   - into the file <file>-<txIndex>.jsonl\n" &
+        "none     - output.basedir/trace-<txIndex>-<txhash>.jsonl\n"
+      defaultValue: none(string)
+      defaultValueDesc: "disabled"
+      name: "trace" }: Option[string]
 
     traceMemory* {.
       desc: "Enable full memory dump in traces"
@@ -166,7 +172,7 @@ proc convertToNimStyle(cmds: openArray[string]): seq[string] =
 
 const
   Copyright = "Copyright (c) 2022 Status Research & Development GmbH"
-  Version   = "Nimbus-t8n 0.1.2"
+  Version   = "Nimbus-t8n 0.2.2"
 
 # force the compiler to instantiate T8NConf.load
 # rather than have to export parseCmdArg

tools/t8n/readme.md

@@ -36,7 +36,11 @@ t8n [OPTIONS]...
 
 The following options are available:
 
- --trace                 Output full trace logs to files trace-<txIndex>-<txhash>.jsonl [=false].
+ --trace                 Enable and set where to put full EVM trace logs [=disabled].
+                             `stdout` - into the stdout output.
+                             `stderr` - into the stderr output.
+                             <file>   - into the file <file>-<txIndex>.jsonl.
+                             none     - output.basedir/trace-<txIndex>-<txhash>.jsonl.
  --trace.memory          Enable full memory dump in traces [=false].
  --trace.nostack         Disable stack output in traces [=false].
  --trace.returndata      Enable return data output in traces [=false].

tools/t8n/t8n_test.nim

@@ -25,6 +25,7 @@ type
     alloc : bool
     result: bool
     body  : bool
+    trace : bool
 
   TestSpec = object
     name       : string
@@ -71,6 +72,9 @@ proc get(opt: T8nOutput): string =
   else:
     result.add(" --output.body")
 
+  if opt.trace:
+    result.add(" --trace stdout")
+
 template exit(jsc: var JsonComparator, msg: string) =
   jsc.path = path
   jsc.error = msg
@@ -137,6 +141,7 @@ proc runTest(appDir: string, spec: TestSpec): bool =
     return false
 
   if spec.expOut.len > 0:
+    if spec.expOut.endsWith(".json"):
       let path = base / spec.expOut
       let want = json.parseFile(path)
       let have = json.parseJson(res)
@@ -147,6 +152,14 @@ proc runTest(appDir: string, spec: TestSpec): bool =
         echo "path: $1, error: $2" %
           [jsc.path, jsc.error]
         return false
+    else:
+      # compare as regular text
+      let path = base / spec.expOut
+      let want = readFile(path)
+      if want.replace("\x0D\x0A", "\n") != res:
+        echo "test $1: output wrong, have \n$2\nwant\n$3\n" %
+          [spec.name, res, want]
+        return false
   return true
 
 const
@@ -484,6 +497,15 @@ const
       output: T8nOutput(alloc: true, result: true),
       expOut: "exp.json",
     ),
+    TestSpec(
+      name  : "EVM tracer crash bug",
+      base  : "testdata/00-519",
+      input : t8nInput(
+        "alloc.json", "txs.json", "env.json", "Shanghai", "0",
+      ),
+      output: T8nOutput(trace: true),
+      expOut: "exp.txt",
+    ),
   ]
 
 proc main() =

tools/t8n/testdata/00-519/alloc.json

@@ -0,0 +1,5 @@
+{
+  "0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b": {
+    "balance": "0x3635c9adc5dea00000"
+  }
+}

tools/t8n/testdata/00-519/env.json

@@ -0,0 +1,20 @@
+{
+  "currentCoinbase": "0x2adc25665018aa1fe0e6bc666dac8fc2697ff9ba",
+  "currentGasLimit": "100000000000000000",
+  "currentNumber": "2",
+  "currentTimestamp": "24",
+  "currentRandom": "0",
+  "currentDifficulty": "0",
+  "blockHashes": {
+    "0": "0xea2d7e0192d890c222f0302d972a02db0bf0c6d08257d73aa1210d08d24f30c3",
+    "1": "0x068f4313da4cb34b1b6b18ff37eb6ca9f7ad9d294357db81c75cb7790d25dd67"
+  },
+  "ommers": [],
+  "withdrawals": [],
+  "parentDifficulty": "0",
+  "parentTimestamp": "12",
+  "parentBaseFee": "7",
+  "parentGasUsed": "0",
+  "parentGasLimit": "100000000000000000",
+  "parentUncleHash": "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347"
+}

tools/t8n/testdata/00-519/exp.txt

@@ -0,0 +1,2 @@
+{"pc":0,"op":0,"gas":"0x0","gasCost":"0xfffffffffffecb68","memSize":0,"stack":[],"depth":1,"refund":0,"opName":"STOP","error":"Blake2b F function invalid input"}
+{"output":"0x","gasUsed":"0x13498","error":"Blake2b F function invalid input"}

tools/t8n/testdata/00-519/txs.json

@@ -0,0 +1,16 @@
+[
+  {
+    "type": "0x0",
+    "chainId": "0x1",
+    "nonce": "0x0",
+    "gasPrice": "0xa",
+    "gas": "0x186a0",
+    "to": "0x0000000000000000000000000000000000000009",
+    "value": "0x0",
+    "input": "0x",
+    "v": "0x26",
+    "r": "0x803b06b78b7bd29d0faf9401f2df5d71e8a445ad1ac0a45d2e5256ba23c43ed1",
+    "s": "0x6634f86b79da86a904b1900a52e470847ffe730ef4ec32a3b0f7eece7bfaae96",
+    "sender": "0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b"
+  }
+]

tools/t8n/transition.nim

@@ -147,18 +147,22 @@ proc calcLogsHash(receipts: openArray[Receipt]): Hash256 =
     logs.add rec.logs
   rlpHash(logs)
 
-template stripLeadingZeros(value: string): string =
-  var cidx = 0
-  # ignore the last character so we retain '0' on zero value
-  while cidx < value.len - 1 and value[cidx] == '0':
-    cidx.inc
-  value[cidx .. ^1]
+proc defaultTraceStream(conf: T8NConf, txIndex: int, txHash: Hash256): Stream =
+  let
+    txHash = "0x" & toLowerAscii($txHash)
+    baseDir = if conf.outputBaseDir.len > 0:
+                conf.outputBaseDir
+              else:
+                "."
+    fName = "$1/trace-$2-$3.jsonl" % [baseDir, $txIndex, txHash]
+  newFileStream(fName, fmWrite)
 
-proc encodeHexInt(x: SomeInteger): JsonNode =
-  %("0x" & x.toHex.stripLeadingZeros.toLowerAscii)
-
-proc toHex(x: Hash256): string =
-  "0x" & x.data.toHex
+proc traceToFileStream(path: string, txIndex: int): Stream =
+  # replace whatever `.ext` to `-${txIndex}.jsonl`
+  let
+    file = path.splitFile
+    fName = "$1/$2-$3.jsonl" % [file.dir, file.name, $txIndex]
+  newFileStream(fName, fmWrite)
 
 proc setupTrace(conf: T8NConf, txIndex: int, txHash: Hash256, vmState: BaseVMstate) =
   var tracerFlags = {
@@ -169,22 +173,20 @@ proc setupTrace(conf: T8NConf, txIndex: int, txHash: Hash256, vmState: BaseVMsta
     TracerFlags.DisableReturnData
   }
 
-  if conf.traceEnabled:
   if conf.traceMemory: tracerFlags.excl TracerFlags.DisableMemory
   if conf.traceNostack: tracerFlags.incl TracerFlags.DisableStack
   if conf.traceReturnData: tracerFlags.excl TracerFlags.DisableReturnData
 
-  let
-    txHash = "0x" & toLowerAscii($txHash)
-    baseDir = if conf.outputBaseDir.len > 0:
-                conf.outputBaseDir
+  let traceMode = conf.traceEnabled.get
+  let stream = if traceMode == "stdout":
+                 newFileStream(stdout)
+               elif traceMode == "stderr":
+                 newFileStream(stderr)
+               elif traceMode.len > 0:
+                 traceToFileStream(traceMode, txIndex)
                else:
-                "."
-    fName = "$1/trace-$2-$3.jsonl" % [baseDir, $txIndex, txHash]
-    stream = newFileStream(fName, fmWrite)
-    tracerInst = newJsonTracer(stream, tracerFlags, false)
-
-  vmState.tracer = tracerInst
+                 defaultTraceStream(conf, txIndex, txHash)
+  vmState.tracer = newJsonTracer(stream, tracerFlags, false)
 
 proc closeTrace(vmState: BaseVMstate) =
   let tracer = JsonTracer(vmState.tracer)
@@ -233,12 +235,12 @@ proc exec(ctx: var TransContext,
       )
       continue
 
-    if conf.traceEnabled:
+    if conf.traceEnabled.isSome:
       setupTrace(conf, txIndex, rlpHash(tx), vmState)
 
     let rc = vmState.processTransaction(tx, sender, header)
 
-    if conf.traceEnabled:
+    if conf.traceEnabled.isSome:
       closeTrace(vmState)
 
     if rc.isErr: