[sanitizer-common] [Darwin] Provide warnings for common sandbox issues (#165907)

We currently do not handle errors in task_set_exc_guard_behavior. If
this fails, mmap can unexpectedly crash.
We also do not currently provide a clear warning if no external
symbolizers are found.

rdar://163798535

Author: ndrewh

compiler-rt/lib/sanitizer_common/sanitizer_mac.cpp

@@ -960,7 +960,17 @@ static void DisableMmapExcGuardExceptions() {
       RTLD_DEFAULT, "task_set_exc_guard_behavior");
   if (set_behavior == nullptr) return;
   const task_exc_guard_behavior_t task_exc_guard_none = 0;
-  set_behavior(mach_task_self(), task_exc_guard_none);
+  kern_return_t res = set_behavior(mach_task_self(), task_exc_guard_none);
+  if (res != KERN_SUCCESS) {
+    Report(
+        "WARN: task_set_exc_guard_behavior returned %d (%s), "
+        "mmap may fail unexpectedly.\n",
+        res, mach_error_string(res));
+    if (res == KERN_DENIED)
+      Report(
+          "HINT: Check that task_set_exc_guard_behavior is allowed by "
+          "sandbox.\n");
+  }
 }
 
 static void VerifyInterceptorsWorking();

compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cpp

@@ -505,6 +505,13 @@ static void ChooseSymbolizerTools(IntrusiveList<SymbolizerTool> *list,
   }
 
 #  if SANITIZER_APPLE
+  if (list->empty()) {
+    Report(
+        "WARN: No external symbolizers found. Symbols may be missing or "
+        "unreliable.\n");
+    Report(
+        "HINT: Is PATH set? Does sandbox allow file-read of /usr/bin/atos?\n");
+  }
   VReport(2, "Using dladdr symbolizer.\n");
   list->push_back(new (*allocator) DlAddrSymbolizer());
 #  endif  // SANITIZER_APPLE