runCode.js: add pc to opt args | initial API tests

docs/index.md

@@ -141,6 +141,7 @@ Runs EVM code
     -   `opts.gasLimit` **[Buffer][42]** the gas limit for the code
     -   `opts.origin` **[Buffer][42]** the address where the call originated from. The address should be a `Buffer` of 20bits. Defaults to `0`
     -   `opts.value` **[Buffer][42]** the value in ether that is being sent to `opt.address`. Defaults to `0`
+    -   `opts.pc` **[Number][32]** the initial program counter. Defaults to `0`
 -   `cb` **[runCode~callback][44]** callback
 
 ## Event: beforeBlock

lib/runCode.js

@@ -38,6 +38,7 @@ const VmError = exceptions.VmError
  * @param {Buffer} opts.gasLimit the gas limit for the code
  * @param {Buffer} opts.origin the address where the call originated from. The address should be a `Buffer` of 20bits. Defaults to `0`
  * @param {Buffer} opts.value the value in ether that is being sent to `opt.address`. Defaults to `0`
+ * @param {Number} opts.pc the initial program counter. Defaults to `0`
  * @param {runCode~callback} cb callback
  */
 
@@ -69,7 +70,7 @@ module.exports = function (opts, cb) {
     returnValue: false,
     stopped: false,
     vmError: false,
-    programCounter: 0,
+    programCounter: opts.pc | 0,
     opCode: undefined,
     opName: undefined,
     gasLeft: new BN(opts.gasLimit),
@@ -108,6 +109,12 @@ module.exports = function (opts, cb) {
 
   // iterate through the given ops until something breaks or we hit STOP
   function runVm (err) {
+    // Check that the programCounter is in range. Does not overwrite the previous err, if any.
+    const pc = runState.programCounter
+    if (!err && pc !== 0 && (pc < 0 || pc >= runState.code.length)) {
+      err = new VmError(ERROR.INVALID_OPCODE)
+    }
+
     if (err) {
       return parseVmResults(err)
     }

tests/programCounter.js

@@ -0,0 +1,58 @@
+const tape = require('tape')
+const async = require('async')
+const VM = require('../')
+
+const STOP = '00'
+const JUMP = '56'
+const JUMPDEST = '5b'
+const PUSH1 = '60'
+
+const testCases = [
+  { code: [STOP, JUMPDEST, PUSH1, '05', JUMP, JUMPDEST], pc: 1, resultPC: 6 },
+  { code: [STOP, JUMPDEST, PUSH1, '05', JUMP, JUMPDEST], pc: -1, error: 'invalid opcode' },
+  { code: [STOP], pc: 3, error: 'invalid opcode' },
+  { code: [STOP], resultPC: 1 }
+]
+
+tape('VM.runcode: initial program counter', function (t) {
+  const vm = new VM()
+
+  testCases.forEach(function (testData, i) {
+    t.test('should start the execution at the specified pc or 0 #' + i, function (st) {
+      const runCodeArgs = {
+        code: Buffer.from(testData.code.join(''), 'hex'),
+        pc: testData.pc,
+        gasLimit: 0xffff
+      }
+      let result
+
+      async.series([
+        function (done) {
+          vm.runCode(runCodeArgs, function (err, res) {
+            if (res) {
+              result = res
+            }
+
+            done(err)
+          })
+        },
+        function (done) {
+          if (testData.resultPC !== undefined) {
+            t.equals(result.runState.programCounter, testData.resultPC, 'runstate.programCounter')
+          }
+
+          done()
+        }
+      ], function (err) {
+        if (testData.error) {
+          err = err ? err.error : 'no error thrown'
+          t.equals(err, testData.error, 'error message should match')
+          err = false
+        }
+
+        t.assert(!err)
+        st.end()
+      })
+    })
+  })
+})

tests/tester.js

@@ -249,6 +249,7 @@ function runAll () {
   require('./tester.js')
   require('./genesishashes.js')
   require('./constantinopleSstoreTest.js')
+  require('./programCounter.js')
   async.series([
     // runTests.bind(this, 'VMTests', {}), // VM tests disabled since we don't support Frontier gas costs
     runTests.bind(this, 'GeneralStateTests', {}),