PR10016: Purge stap of all pgrp and system() usage

We hereby no longer try to manipulate process groups in any way.  We
don't set a private process group, and we never kill() our entire group
either.  Instead of using system(), we now have a stap_system() which
saves the child PID, so when we get a terminating signal we can pass it
along to the child.

Signals sent through the TTY have always worked, since the TTY sends it
to the entire pgrp.  However, if we're running as part of a wrapper
script or GUI, which may not have a separate process group for stap, we
still would like to allow "kill -TERM $STAPPID" to terminate stap
nicely.

There's still a short window of failure in the time that staprun is
active, because we can't kill a setuid process from a user process.
Once staprun drops privileges and execs to stapio though, everything
should work fine.

1 files changed, 4 insertions, 73 deletions

diff --git a/main.cxx b/main.cxx
index 3b88a1c8..794a5891 100644
--- a/main.cxx
+++ b/main.cxx
@@ -36,8 +36,6 @@ extern "C" {
 #include <sys/times.h>
 #include <sys/time.h>
 #include <sys/stat.h>
-#include <sys/types.h>
-#include <sys/wait.h>
 #include <time.h>
 #include <elfutils/libdwfl.h>
 #include <getopt.h>
@@ -293,14 +291,9 @@ int pending_interrupts;
 extern "C"
 void handle_interrupt (int sig)
 {
-  if (pending_interrupts == 0)
-    kill (0, sig); // Forward signals to child processes if any.
-
+  kill_stap_spawn(sig);
   pending_interrupts ++;
-  // NB: the "2" below is intended to skip the effect of the self-induced
-  // deferred signal coming from the kill() above.
-
-  if (pending_interrupts > 2) // XXX: should be configurable? time-based?
+  if (pending_interrupts > 1) // XXX: should be configurable? time-based?
     {
       char msg[] = "Too many interrupts received, exiting.\n";
       int rc = write (2, msg, sizeof(msg)-1);
@@ -324,7 +317,7 @@ setup_signals (sighandler_t handler)
       sigaddset (&sa.sa_mask, SIGINT);
       sigaddset (&sa.sa_mask, SIGTERM);
     }
-  sa.sa_flags = 0;
+  sa.sa_flags = SA_RESTART;
 
   sigaction (SIGHUP, &sa, NULL);
   sigaction (SIGPIPE, &sa, NULL);
@@ -332,62 +325,10 @@ setup_signals (sighandler_t handler)
   sigaction (SIGTERM, &sa, NULL);
 }
 
-pid_t runner_pid;
-int runner (int, char * const []);
-
-// Passes on signals to runner process.
-// In practise passes signal to runner process process group,
-// since run_pass() uses system() to spawn child processes,
-// which makes the process ignore SIGINT during the command run.
-extern "C"
-void waiter_handler (int sig)
-{
-  // Process group is negative process id.
-  kill (-1 * runner_pid, sig);
-}
-
-// Just sits there till the runner exits and then exits the same way.
-void waiter()
-{
-  int status;
-  setup_signals (&waiter_handler);
-  while (waitpid (runner_pid, &status, 0) != runner_pid);
-
-  // Exit as our runner child exitted.
-  if (WIFEXITED(status))
-    exit (WEXITSTATUS(status));
-
-  // Or simulate as if we were killed by the same signal.
-  if (WIFSIGNALED(status))
-    {
-      int sig = WTERMSIG(status);
-      signal (sig, SIG_DFL);
-      raise (sig);
-    }
-
-  // Should not happen, exit as if error.
-  exit(-1);
-}
 
 int
 main (int argc, char * const argv [])
 {
-  // Fork to make sure runner gets its own process group, while
-  // the waiter sits in the original process group of the shell
-  // and forwards any signals.
-  runner_pid = fork ();
-  if (runner_pid == 0)
-    return runner (argc, argv);
-  if (runner_pid > 0)
-    waiter ();
-
-  perror ("couldn't fork");
-  exit (-1);
-}
-
-int
-runner (int argc, char * const argv [])
-{
   string cmdline_script; // -e PROGRAM
   string script_file; // FILE
   bool have_script = false;
@@ -899,16 +840,6 @@ runner (int argc, char * const argv [])
   // directory.
   s.translated_source = string(s.tmpdir) + "/" + s.module_name + ".c";
 
-  // We want a new process group so we can use kill (0, sig) to send a
-  // signal to all children (but not the parent).  As done in
-  // handle_interrupt ().
-  if (setpgrp() != 0)
-    {
-      const char* e = strerror (errno);
-      if (! s.suppress_warnings)
-        cerr << "Warning: failed to set new process group: " << e << endl;
-    }
-
   // Set up our handler to catch routine signals, to allow clean
   // and reasonably timely exit.
   setup_signals(&handle_interrupt);
@@ -1251,7 +1182,7 @@ pass_5:
           string cleanupcmd = "rm -rf ";
           cleanupcmd += s.tmpdir;
           if (s.verbose>1) clog << "Running " << cleanupcmd << endl;
-	  int status = system (cleanupcmd.c_str());
+	  int status = stap_system (cleanupcmd.c_str());
 	  if (status != 0 && s.verbose>1)
 	    clog << "Cleanup command failed, status: " << status << endl;
         }