Index: lib/dfsan/dfsan_custom.cc
===================================================================
--- lib/dfsan/dfsan_custom.cc
+++ lib/dfsan/dfsan_custom.cc
@@ -1132,4 +1132,26 @@
   va_end(ap);
   return ret;
 }
-} // extern "C"
+
+// Default empty implementations (weak). Users should redefine them.
+SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_pc_guard, u32 *) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_pc_guard_init, u32 *,
+                             u32 *) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_pcs_init, void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __sanitizer_cov_trace_pc_indir, void) {}
+
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_cmp, void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_cmp1, void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_cmp2, void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_cmp4, void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_cmp8, void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_const_cmp1,
+                             void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_const_cmp2,
+                             void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_const_cmp4,
+                             void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_const_cmp8,
+                             void) {}
+SANITIZER_INTERFACE_WEAK_DEF(void, __dfsw___sanitizer_cov_trace_switch, void) {}
+}  // extern "C"
Index: lib/dfsan/scripts/check_custom_wrappers.sh
===================================================================
--- lib/dfsan/scripts/check_custom_wrappers.sh
+++ lib/dfsan/scripts/check_custom_wrappers.sh
@@ -23,6 +23,7 @@
   | grep -v "dfsan_get_label\|__sanitizer_cov_trace" \
   | sed "s/^fun:\(.*\)=custom.*/\1/" | sort > $DIFF_A
 grep -E "__dfsw.*\(" ${DFSAN_CUSTOM_WRAPPERS} \
+  | grep -v "__sanitizer_cov_trace" \
   | sed "s/.*__dfsw_\(.*\)(.*/\1/" | sort > $DIFF_B
 diff -u $DIFF_A $DIFF_B > ${DIFFOUT}
 if [ $? -ne 0 ]
@@ -33,6 +34,7 @@
 fi
 
 grep -E __dfsw_ ${DFSAN_CUSTOM_WRAPPERS} \
+  | grep -v "__sanitizer_cov_trace" \
   | sed "s/.*__dfsw_\([^(]*\).*/\1/" | sort > $DIFF_A
 grep -E "^[[:space:]]*test_.*\(\);" ${DFSAN_CUSTOM_TESTS} \
   | sed "s/.*test_\(.*\)();/\1/" | sort > $DIFF_B
Index: test/dfsan/trace-cmp.c
===================================================================
--- test/dfsan/trace-cmp.c
+++ test/dfsan/trace-cmp.c
@@ -0,0 +1,50 @@
+// Checks that dfsan works with trace-cmp instrumentation, even if some hooks
+// are not defined (relies on week hooks implemented in dfsan).
+//
+// RUN: %clang_dfsan -fsanitize-coverage=trace-pc-guard,pc-table,func,trace-cmp %s -o %t
+// RUN: %run %t 2>&1 | FileCheck %s
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include <sanitizer/dfsan_interface.h>
+
+uint32_t a4, b4;
+uint64_t a8, b8;
+
+// Define just two hooks, and leave others undefined.
+void __dfsw___sanitizer_cov_trace_const_cmp4(uint8_t a, uint8_t b,
+                                             dfsan_label l1, dfsan_label l2) {
+  printf("const_cmp4 %d %d\n", a, b);
+}
+void __dfsw___sanitizer_cov_trace_cmp8(uint8_t a, uint8_t b, dfsan_label l1,
+                                       dfsan_label l2) {
+  printf("cmp8 %d %d\n", a, b);
+}
+
+int main(int argc, char **argv) {
+  printf("MAIN\n");
+  // CHECK: MAIN
+
+  if (a4 != b4) abort();
+  if (a4 == 42) abort();
+  // CHECK: const_cmp4 42 0
+  if (a8 != b8) abort();
+  // CHECK: cmp8 0 0
+  if (a8 == 66) abort();
+
+  switch (10 / (a4 + 2)) {
+    case 1: abort();
+    case 2: exit(1);
+    case 5:
+            printf("SWITCH OK\n");
+            break;
+  }
+  // CHECK: SWITCH OK
+
+
+  printf("DONE\n");
+  // CHECK: DONE
+  return 0;
+}