[asan] Fix dyld version detection on OS X

[kubamracek]

Summary

We currently have a dyld check in DyldNeedsEnvVariable that detects whether we are on a new OS X (10.11+) where we don't need to re-exec. For iOS simulator, we have a dlsym() hack that checks for a specific symbol, but this turns out to be fragile and problematic, because dlsym can sometimes call malloc(), which is not a good idea this early in the process runtime.

Let's instead of this do a direct comparison of dyld's version, which is exported in a public symbol dyldVersionNumber.

[glider]

LGTM

lib/asan/asan_mac.cc

108

Nit: spare newline?

[ygribov]

Could someone check this: https://github.com/google/sanitizers/issues/669 ? Seems to be caused by this patch.

lib/asan/asan_mac.cc

 }
 
 static bool reexec_disabled = false;
 
 void DisableReexec() {
   reexec_disabled = true;
 }
 
+extern "C" double dyldVersionNumber;
+static const double kMinDyldVersionWithAutoInterposition = 360.0;
+
 bool DyldNeedsEnvVariable() {
   // If running on OS X 10.11+ or iOS 9.0+, dyld will interpose even if
   // DYLD_INSERT_LIBRARIES is not set.
 
-#if SANITIZER_IOSSIM
-  // GetMacosVersion will not work for the simulator, whose kernel version
-  // is tied to the host. Use a weak linking hack for the simulator.
-  // This API was introduced in the same version of the OS as the dyld
-  // optimization.
-
-  // Check for presence of a symbol that is available on OS X 10.11+, iOS 9.0+.
-  return (dlsym(RTLD_NEXT, "mach_memory_info") == nullptr);
-#else
-  return (GetMacosVersion() <= MACOS_VERSION_YOSEMITE);
-#endif
+  // However, checking OS version via GetMacosVersion() doesn't work for the
+  // simulator. Let's instead check `dyldVersionNumber`, which is exported by
+  // dyld, against a known version number from OS release where this appeared.
+  return dyldVersionNumber < kMinDyldVersionWithAutoInterposition;
 }
 
 void MaybeReexec() {
   if (reexec_disabled) return;
 
   // Make sure the dynamic ASan runtime library is preloaded so that the
   // wrappers work. If it is not, set DYLD_INSERT_LIBRARIES and re-exec
   // ourselves.