[DFSan] Add custom wrapper for pthread_join.

[morehouse]

Summary

The wrapper clears shadow for retval.

[stephan.yichao.zhao]

compiler-rt/test/dfsan/custom.cpp

800

Do we also check &cbrv is not changed?

[morehouse]

compiler-rt/test/dfsan/custom.cpp

800

How would it change? It's on the stack.

[stephan.yichao.zhao]

compiler-rt/test/dfsan/custom.cpp

800

My question was confusing.

Since pthread_join takes "void **retval", do we also check *retval has zero shadow?

[morehouse]

compiler-rt/test/dfsan/custom.cpp

800

Yes, it is checked by this line actually.
&cbrv == retval, therefore cbrv == *retval.

[stephan.yichao.zhao]

compiler-rt/test/dfsan/custom.cpp

800

Thank you for explaining this. We cannot test dfsan_read_label(&cbrv, sizeof(cbrv)) because *cbrv is actually 2.

compiler-rt/lib/dfsan/dfsan_custom.cpp

SANITIZER_INTERFACE_ATTRIBUTE int __dfsw_pthread_create(
   pci->arg = arg;
   int rv = pthread_create(thread, attr, pthread_create_cb, (void *)pci);
   if (rv != 0)
     free(pci);
   *ret_label = 0;
   return rv;
 }
 
+SANITIZER_INTERFACE_ATTRIBUTE int __dfsw_pthread_join(pthread_t thread,
+                                                      void **retval,
+                                                      dfsan_label thread_label,
+                                                      dfsan_label retval_label,
+                                                      dfsan_label *ret_label) {
+  int ret = pthread_join(thread, retval);
+  if (ret == 0 && retval)
+    dfsan_set_label(0, retval, sizeof(*retval));
+  *ret_label = 0;
+  return ret;
+}
+
 struct dl_iterate_phdr_info {
   int (*callback_trampoline)(void *callback, struct dl_phdr_info *info,
                              size_t size, void *data, dfsan_label info_label,
                              dfsan_label size_label, dfsan_label data_label,
                              dfsan_label *ret_label);
   void *callback;
   void *data;
 };

compiler-rt/lib/dfsan/done_abilist.txt

 fun:pthread_setname_np=discard
 fun:pthread_once=discard
 fun:pthread_self=discard
 fun:pthread_setspecific=discard
 
 # Functions that take a callback (wrap the callback manually).
 fun:pthread_create=custom
 
+# Functions that produce output does not depend on the input (need to zero the
+# shadow manually).
+fun:pthread_join=custom
+
 ###############################################################################
 # libffi/libgo
 ###############################################################################
 # Functions that are written in asm or are called from asm.
 fun:ffi_call_unix64=uninstrumented
 fun:ffi_call_unix64=discard
 fun:ffi_closure_unix64_inner=uninstrumented
 fun:ffi_closure_unix64_inner=discard

compiler-rt/test/dfsan/custom.cpp

void *pthread_create_test_cb(void *p) {
   ASSERT_ZERO_LABEL(p);
   return (void *)2;
 }
 
 void test_pthread_create() {
   pthread_t pt;
   pthread_create(&pt, 0, pthread_create_test_cb, (void *)1);
   void *cbrv;
-  pthread_join(pt, &cbrv);
+  dfsan_set_label(i_label, &cbrv, sizeof(cbrv));
+  int ret = pthread_join(pt, &cbrv);
+  assert(ret == 0);
   assert(cbrv == (void *)2);
+  ASSERT_ZERO_LABEL(ret);
+  ASSERT_ZERO_LABEL(cbrv);
 }
 
 int dl_iterate_phdr_test_cb(struct dl_phdr_info *info, size_t size,
                             void *data) {
   assert(data == (void *)3);
   ASSERT_ZERO_LABEL(info);
   ASSERT_ZERO_LABEL(size);
   ASSERT_ZERO_LABEL(data);