Index: compiler-rt/lib/sanitizer_common/sanitizer_printf.cpp
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_printf.cpp
+++ compiler-rt/lib/sanitizer_common/sanitizer_printf.cpp
@@ -229,15 +229,15 @@
 // Can be overriden in frontend.
 #if SANITIZER_GO && defined(TSAN_EXTERNAL_HOOKS)
 // Implementation must be defined in frontend.
-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) {
-  OnPrint(str);
+  __sanitizer_on_print(str);
   if (PrintfAndReportCallback)
     PrintfAndReportCallback(str);
 }
Index: compiler-rt/test/sanitizer_common/TestCases/onprint.cpp
===================================================================
--- /dev/null
+++ compiler-rt/test/sanitizer_common/TestCases/onprint.cpp
@@ -0,0 +1,31 @@
+// 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;
+}