[fuzzer] Use RawPrint instead of Printf for instrumentation warning

[metzman]

Summary

Use RawPrint instead of Printf for instrumentation warning because
Printf doesn't yet work when instrumentation is being initialized
(since OutputFile is not yet initialized).

[metzman]

Please take a look.
This fixes the deprecated-instrumentation.test which is currently failing on Windows because the message doesn't print.
It doesn't print because OutputFile in FuzzerIO.cpp is not yet initialized when WarnAboutDeprecatedInstrumentation is called.
An alternative to this fix is just disabling the test on Windows, I don't worry much about the message not being printed because I don't think anyone has ever used trace-pc on Win with libFuzzer.

[kcc]

LGTM, thanks!

[metzman]

• fmt

[metzman]

commit message

lib/fuzzer/FuzzerIOWindows.cpp

if (FileName.find("compiler-rt\\lib\\") != std::string::npos)
     return false; // sanitizer internal.
   if (FileName == "<null>")
     return false;
   return true;
 }
 
 void RawPrint(const char *Str) {
   // Not tested, may or may not work. Fix if needed.
-  Printf("%s", Str);
+  write(2, Str, strlen(Str));
 }
 
 }  // namespace fuzzer
 
 #endif // LIBFUZZER_WINDOWS

lib/fuzzer/FuzzerTracePC.cpp

void TracePC::RecordInitialStack() {
   __sancov_lowest_stack = InitialStack = reinterpret_cast<uintptr_t>(&stack);
 }
 
 uintptr_t TracePC::GetMaxStackOffset() const {
   return InitialStack - __sancov_lowest_stack;  // Stack grows down
 }
 
 void WarnAboutDeprecatedInstrumentation(const char *flag) {
-  Printf("libFuzzer does not support %s any more.\n"
-         "Please either migrate to a compiler that supports -fsanitize=fuzzer\n"
-         "or use an older version of libFuzzer\n", flag);
+  // Use RawPrint because Printf cannot be used on Windows before OutputFile is
+  // initialized.
+  RawPrint(flag);
+  RawPrint(
+      " is no longer supported by libFuzzer.\n"
+      "or use an older version of libFuzzer\n");
   exit(1);
 }
 
 } // namespace fuzzer
 
 extern "C" {
 ATTRIBUTE_INTERFACE
 ATTRIBUTE_NO_SANITIZE_ALL
 void __sanitizer_cov_trace_pc_guard(uint32_t *Guard) {
-  fuzzer::WarnAboutDeprecatedInstrumentation("-fsanitize-coverage=trace-pc");
+  fuzzer::WarnAboutDeprecatedInstrumentation(
+      "-fsanitize-coverage=trace-pc-guard");
 }
 
 // Best-effort support for -fsanitize-coverage=trace-pc, which is available
 // in both Clang and GCC.
 ATTRIBUTE_INTERFACE
 ATTRIBUTE_NO_SANITIZE_ALL
 void __sanitizer_cov_trace_pc() {
-  fuzzer::WarnAboutDeprecatedInstrumentation(
-      "-fsanitize-coverage=trace-pc-guard");
+  fuzzer::WarnAboutDeprecatedInstrumentation("-fsanitize-coverage=trace-pc");
 }
 
 ATTRIBUTE_INTERFACE
 void __sanitizer_cov_trace_pc_guard_init(uint32_t *Start, uint32_t *Stop) {
   fuzzer::WarnAboutDeprecatedInstrumentation(
       "-fsanitize-coverage=trace-pc-guard");
 }
 

test/fuzzer/deprecated-instrumentation.test

-CHECK: libFuzzer does not support -fsanitize-coverage=trace-pc
+CHECK: -fsanitize-coverage=trace-pc is no longer supported by libFuzzer
 RUN: %cpp_compiler %S/SimpleTest.cpp -c -o %t-SimpleTest.o -fsanitize-coverage=trace-pc
 RUN: %cpp_compiler %t-SimpleTest.o -o %t-SimpleTest
 RUN: not %run %t-SimpleTest 2>&1 | FileCheck %s