Add test for Flags.data_flow_trace

[yingcong-wu]

Summary

CollectDataFlow() uses Flags.collect_data_flow and
Flags.data_flow_trace at the same time. But in the null check before
the invocation, only Flags.collect_data_flow is checked, and there is
no other method to make sure Flags.data_flow_trace is not null, so
adding a null check for Flags.data_flow_trace.

[karapsinie]

arc diff git merge-base HEAD origin --update D145040

[karapsinie]

Attempt to restore.
Sorry for the breakdown. Please tell me how to fix what was done?

[vitalybuka]

test

compiler-rt/lib/fuzzer/FuzzerDriver.cpp

int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
   unsigned Seed = Flags.seed;
   // Initialize Seed.
   if (Seed == 0)
     Seed = static_cast<unsigned>(
         std::chrono::system_clock::now().time_since_epoch().count() + GetPid());
   if (Flags.verbosity)
     Printf("INFO: Seed: %u\n", Seed);
 
-  if (Flags.collect_data_flow && !Flags.fork &&
+  if (Flags.collect_data_flow && Flags.data_flow_trace && !Flags.fork &&
       !(Flags.merge || Flags.set_cover_merge)) {
     if (RunIndividualFiles)
       return CollectDataFlow(Flags.collect_data_flow, Flags.data_flow_trace,
                         ReadCorpora({}, *Inputs));
     else
       return CollectDataFlow(Flags.collect_data_flow, Flags.data_flow_trace,
                         ReadCorpora(*Inputs, {}));
   }

compiler-rt/test/fuzzer/dataflow.test

 L20_FUZZ-NOT: F
 
 RUN:%t-Labels20TestDF %t/IN20/FUZZxxxxxxxxxxxxMxxx | FileCheck %s --check-prefix=L20_FUZZM
 L20_FUZZM: F0 11110000000000000000{{$}}
 L20_FUZZM-NEXT: F1 00000000000000001000{{$}}
 L20_FUZZM-NEXT: F2 00000000000000000001{{$}}
 L20_FUZZM-NOT: F
 
+# Don't crash with missing data_flow args.
+RUN: rm -rf %t-DFT
+RUN: %t-ThreeFunctionsTest -collect_data_flow=%t-ThreeFunctionsTestDF
+RUN: %t-ThreeFunctionsTest -data_flow_trace=%t-DFT %t/IN/FUZZMU
+
 # Test libFuzzer's built in DFT collection.
 RUN: rm -rf %t-DFT
 RUN: %t-ThreeFunctionsTest  -collect_data_flow=%t-ThreeFunctionsTestDF -data_flow_trace=%t-DFT %t/IN/FUZZMU
 RUN: cat %t-DFT/* | sort | FileCheck %s --check-prefix=IN_FUZZMU
 
 IN_FUZZMU: F0 111100
 IN_FUZZMU: F1 000010
 IN_FUZZMU: F2 000001