[PATCH] driver: ignore SIGINT while waiting on subprocesses to finish

[Patrick Palka]

Currently the top-level driver handles SIGINT by immediately killing
itself even when the driver has subprocesses (e.g. cc1, as) running.  I
don't think this is a good idea because

  1. if the top-level driver is waiting on a hanging subprocess,
  pressing ^C will kill the driver but it may not necessarily kill the
  subprocess; an unresponsive, perhaps busy-looping subprocess may be
  running in the background yet the compiler will seem to have to
  terminated successfully.

  2. when debugging gcc with "gcc -wrapper gdb,--args" we are unable to
  use ^C from within the GDB subprocess because pressing ^C immediately
  kills the driver and we lose our terminal.  This makes debugging more
  inconvenient.

This patch fixes these two issues by having the driver ignore SIGINT
while a subprocess is running.  The driver instead will have to wait for
the subprocess to exit before it terminates, like usual.

I tested this change by running "gcc -wrapper gdb", "gcc -wrapper
valgrind" and plain old "gcc" in various ways (-pipe, -flto, -c, etc)
and pressing ^C during compilation.  I noticed no differences in
behavior or promptness other than finally being able to use ^C inside
GDB.

Does this change look OK for trunk after a successful bootstrap +
regtest on x86_64-unknown-linux-gnu?
---
 gcc/gcc.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/gcc/gcc.c b/gcc/gcc.c
index 653ca8d..0802f41 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -2653,7 +2653,11 @@ add_sysrooted_prefix (struct path_prefix *pprefix, const char *prefix,
   add_prefix (pprefix, prefix, component, priority,
 	      require_machine_suffix, os_multilib);
 }
-
+
+/* True if the SIGINT signal should be ignored by the driver's
+   signal handler.  */
+static bool ignore_sigint_p;
+
 /* Execute the command specified by the arguments on the current line of spec.
    When using pipes, this includes several piped-together commands
    with `|' between them.
@@ -2839,6 +2843,10 @@ execute (void)
   if (pex == NULL)
     fatal_error ("pex_init failed: %m");
 
+  /* A SIGINT raised while subprocesses are running should not kill the
+     driver.  */
+  ignore_sigint_p = true;
+
   for (i = 0; i < n_commands; i++)
     {
       const char *errmsg;
@@ -2878,6 +2886,8 @@ execute (void)
     if (!pex_get_status (pex, n_commands, statuses))
       fatal_error ("failed to get exit status: %m");
 
+    ignore_sigint_p = false;
+
     if (report_times || report_times_to_file)
       {
 	times = (struct pex_time *) alloca (n_commands * sizeof (struct pex_time));
@@ -2893,6 +2903,9 @@ execute (void)
 
 	if (WIFSIGNALED (status))
 	  {
+	    if (WTERMSIG (status) == SIGINT)
+	      raise (SIGINT);
+	    else
 #ifdef SIGPIPE
 	    /* SIGPIPE is a special case.  It happens in -pipe mode
 	       when the compiler dies before the preprocessor is done,
@@ -6710,6 +6723,12 @@ set_input (const char *filename)
 static void
 fatal_signal (int signum)
 {
+  if (signum == SIGINT && ignore_sigint_p)
+    {
+      signal (signum, fatal_signal);
+      return;
+    }
+
   signal (signum, SIG_DFL);
   delete_failure_queue ();
   delete_temp_files ();
-- 
2.2.0.rc1.23.gf570943