Fix check of the return code from std::system to correctly determine if the

command crashed.

Author: tarunprabhu

tools/not.cpp

@@ -52,7 +52,8 @@ int main(int argc, const char **argv) {
   for (int i = 1; i < argc; ++i)
     ss << " " << argv[i];
   std::string cmd = ss.str();
-  int result = system(cmd.c_str());
+
+  int result = std::system(cmd.c_str());
 
 #ifdef _WIN32
   // Handle abort() in msvcrt -- It has exit code as 3.  abort(), aka
@@ -63,14 +64,23 @@ int main(int argc, const char **argv) {
     result = -3;
 #endif
 
-  if (result < 0) {
+  // On POSIX systems, result is a composite value of the exit status and,
+  // potentially, the signal that caused termination of the command.
+  int retcode = WEXITSTATUS(result);
+  int signal = WTERMSIG(result);
+
+  // If signal is non-zero, then the command caused a crash, usually SIGABRT.
+  if (signal) {
     if (expectCrash)
       return 0;
     return 1;
   }
 
+  // The command exited normally, but if we expected a crash, return an error
+  // code.
   if (expectCrash)
     return 1;
 
-  return result == 0;
+  // Otherwise, invert the success code.
+  return retcode == EXIT_SUCCESS;
 }