[sanitizer_common] Rename OnPrint to __sanitizer_on_print.

[morehouse]

Summary

https://reviews.llvm.org/D28596 exposed OnPrint in the global namespace,
which can cause collisions with user-defined OnPrint() functions.

[dvyukov]

For the Go version we have a non-weak declaration without definition. How are we going to roll out the change? We would need to update llvm and the hook implementation atomically. But then I am confused how it works today. We have a non-extern "C" hook definition, so build should be broken for the last year...

[morehouse]

I don't see TSAN_EXTERNAL_HOOKS defined anywhere internally. So presumably the non-weak declaration was never used.

[morehouse]

Hmm.. Actually it is defined. I'll have to look into it more...

[morehouse]

• Keep Go's OnPrint declaration for now.

[morehouse]

In D67987#1684026, @dvyukov wrote:

For the Go version we have a non-weak declaration without definition. How are we going to roll out the change? We would need to update llvm and the hook implementation atomically. But then I am confused how it works today. We have a non-extern "C" hook definition, so build should be broken for the last year...

I'm also not sure exactly why it's working internally. Apparently the extern "C" doesn't matter when compiling the race detector stuff, but I do get a linking error if I change the symbol name.

Let's temporarily keep the OnPrint symbol for Go. This will give us time to migrate to __sanitizer_on_print internally and then remove OnPrint here.

compiler-rt/lib/sanitizer_common/sanitizer_printf.cpp

 static void (*PrintfAndReportCallback)(const char *);
 void SetPrintfAndReportCallback(void (*callback)(const char *)) {
   PrintfAndReportCallback = callback;
 }
 
 // Can be overriden in frontend.
 #if SANITIZER_GO && defined(TSAN_EXTERNAL_HOOKS)
 // Implementation must be defined in frontend.
+// TODO(morehouse): Remove OnPrint after migrating Go to __sanitizer_on_print.
 extern "C" void OnPrint(const char *str);
+extern "C" void __sanitizer_on_print(const char *str);
 #else
-SANITIZER_INTERFACE_WEAK_DEF(void, OnPrint, const char *str) {
+SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_on_print, const char *str) {
   (void)str;
 }
 #endif
 
 static void CallPrintfAndReportCallback(const char *str) {
+#if SANITIZER_GO && defined(TSAN_EXTERNAL_HOOKS)
+  // TODO(morehouse): Remove OnPrint after migrating Go to __sanitizer_on_print.
   OnPrint(str);
+#endif
+  __sanitizer_on_print(str);
   if (PrintfAndReportCallback)
     PrintfAndReportCallback(str);
 }
 
 static void NOINLINE SharedPrintfCodeNoBuffer(bool append_pid,
                                               char *local_buffer,
                                               int buffer_size,
                                               const char *format,

compiler-rt/test/sanitizer_common/TestCases/onprint.cpp

+// Checks that the __sanitizer_on_print hook gets the exact same sanitizer
+// report as what is printed to stderr.
+//
+// RUN: %clangxx %s -o %t
+// RUN: %run %t %t-onprint.txt 2>%t-stderr.txt || true
+// RUN: diff %t-onprint.txt %t-stderr.txt
+
+#include <cassert>
+#include <cstdio>
+#include <cstdlib>
+
+FILE *f;
+volatile void *buf;
+volatile char sink;
+
+extern "C" void __sanitizer_on_print(const char *str) {
+  fprintf(f, "%s", str);
+  fflush(f);
+}
+
+int main(int argc, char *argv[]) {
+  assert(argc >= 2);
+  f = fopen(argv[1], "w");
+
+  // Use-after-free to trigger ASan/TSan reports.
+  void *ptr = malloc(1);
+  buf = ptr;
+  free(ptr);
+  sink = *static_cast<char *>(ptr);
+  return 0;
+}