[asan] Replace vfork with fork.

[eugenis]

Summary

vfork is not ASan-friendly because it modifies stack shadow in the
parent process address space. While it is possible to compensate for that with, for example,
__asan_handle_no_return before each call to _exit or execve and friends, simply replacing
vfork with fork looks like by far the easiest solution.

Posix compliant programs can not detect the difference between vfork and fork.

Fixes https://github.com/google/sanitizers/issues/925

compiler-rt/trunk/lib/asan/asan_interceptors.h

 
 // Use macro to describe if specific function should be
 // intercepted on a given platform.
 #if !SANITIZER_WINDOWS
 # define ASAN_INTERCEPT_ATOLL_AND_STRTOLL 1
 # define ASAN_INTERCEPT__LONGJMP 1
 # define ASAN_INTERCEPT_INDEX 1
 # define ASAN_INTERCEPT_PTHREAD_CREATE 1
+# define ASAN_INTERCEPT_VFORK 1
 #else
 # define ASAN_INTERCEPT_ATOLL_AND_STRTOLL 0
 # define ASAN_INTERCEPT__LONGJMP 0
 # define ASAN_INTERCEPT_INDEX 0
 # define ASAN_INTERCEPT_PTHREAD_CREATE 0
+# define ASAN_INTERCEPT_VFORK 0
 #endif
 
 #if SANITIZER_FREEBSD || SANITIZER_LINUX || SANITIZER_NETBSD || \
     SANITIZER_SOLARIS
 # define ASAN_USE_ALIAS_ATTRIBUTE_FOR_INDEX 1
 #else
 # define ASAN_USE_ALIAS_ATTRIBUTE_FOR_INDEX 0
 #endif

compiler-rt/trunk/lib/asan/asan_interceptors.cc

 #endif
   ENSURE_ASAN_INITED();
   int res = REAL(__cxa_atexit)(func, arg, dso_handle);
   REAL(__cxa_atexit)(AtCxaAtexit, nullptr, nullptr);
   return res;
 }
 #endif  // ASAN_INTERCEPT___CXA_ATEXIT
 
+#if ASAN_INTERCEPT_VFORK
+extern "C" int fork(void);
+INTERCEPTOR(int, vfork, void) {
+  return fork();
+}
+#endif  // ASAN_INTERCEPT_VFORK
+
 // ---------------------- InitializeAsanInterceptors ---------------- {{{1
 namespace __asan {
 void InitializeAsanInterceptors() {
   static bool was_called_once;
   CHECK(!was_called_once);
   was_called_once = true;
   InitializeCommonInterceptors();
   InitializeSignalInterceptors();
#endif
   ASAN_INTERCEPT_FUNC(pthread_join);
 #endif
 
   // Intercept atexit function.
 #if ASAN_INTERCEPT___CXA_ATEXIT
   ASAN_INTERCEPT_FUNC(__cxa_atexit);
 #endif
 
+#if ASAN_INTERCEPT_VFORK
+  ASAN_INTERCEPT_FUNC(vfork);
+#endif
+
   InitializePlatformInterceptors();
 
   VReport(1, "AddressSanitizer: libc interceptors initialized\n");
 }
 
 } // namespace __asan
 
 #endif  // !SANITIZER_FUCHSIA

compiler-rt/trunk/test/asan/TestCases/Posix/vfork.cc

+// Test that vfork() is fork().
+// https://github.com/google/sanitizers/issues/925
+
+// RUN: %clangxx_asan -O0 %s -o %t && %run %t 2>&1
+
+#include <assert.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+int volatile global;
+
+int main(int argc, char **argv) {
+  pid_t pid = vfork();
+  if (pid) {
+    // parent
+    int status;
+    int res;
+    do {
+      res = waitpid(pid, &status, 0);
+    } while (res >= 0 && !WIFEXITED(status) && !WIFSIGNALED(status));
+    assert(global == 0);
+  } else {
+    // child
+    global = 42;
+    _exit(0);
+  }
+
+  return 0;
+}