[ASan] Allow new/delete replacement by making interceptors weak

ASan declares these functions as strongly-defined, which results in
'duplicate symbol' errors when trying to replace them in user code when
linking the runtimes statically.

Reviewed By: eugenis

Differential Revision: https://reviews.llvm.org/D100220

compiler-rt/lib/asan/asan_new_delete.cpp

@@ -45,7 +45,7 @@ COMMENT_EXPORT("??_V@YAXPAX@Z")                   // operator delete[]
 #endif
 #undef COMMENT_EXPORT
 #else
-#define CXX_OPERATOR_ATTRIBUTE INTERCEPTOR_ATTRIBUTE
+#define CXX_OPERATOR_ATTRIBUTE INTERCEPTOR_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
 #endif
 
 using namespace __asan;

compiler-rt/test/asan/TestCases/replaceable_new_delete.cpp

@@ -0,0 +1,28 @@
+// Ensure that operator new/delete are still replaceable.
+
+// RUN: %clangxx %s -o %t -fsanitize=address -shared-libsan && not %run %t 2>&1 | FileCheck %s
+// RUN: %clangxx %s -o %t -fsanitize=address -static-libsan && not %run %t 2>&1 | FileCheck %s
+
+#include <cstdio>
+#include <cstdlib>
+#include <new>
+
+void *operator new[](size_t size) {
+  fprintf(stderr, "replaced new\n");
+  return malloc(size);
+}
+
+void operator delete[](void *ptr) noexcept {
+  fprintf(stderr, "replaced delete\n");
+  return free(ptr);
+}
+
+int main(int argc, char **argv) {
+  // CHECK: replaced new
+  char *x = new char[5];
+  // CHECK: replaced delete
+  delete[] x;
+  // CHECK: ERROR: AddressSanitizer
+  *x = 13;
+  return 0;
+}