[PATCH v4 8/8] Forced quit cases handled by resetting sync_quit_force_run

[Kevin Buettner <kevinb@redhat.com>]

During my audit of the use of gdb_exception with regard to QUIT
processing, I found a try/catch in the scoped_switch_fork_info
destructor.

Static analysis found this call path from the destructor to
maybe_quit():

  scoped_switch_fork_info::~scoped_switch_fork_info()
    -> remove_breakpoints()
    -> remove_breakpoint(bp_location*)
    -> remove_breakpoint_1(bp_location*, remove_bp_reason)
    -> memory_validate_breakpoint(gdbarch*, bp_target_info*)
    -> target_read_memory(unsigned long, unsigned char*, long)
    -> target_read(target_ops*, target_object, char const*, unsigned char*, unsigned long, long)
    -> maybe_quit()

Since it's not safe to do a 'throw' from a destructor, we simply
call set_quit_flag and, for gdb_exception_forced_quit, also
set sync_quit_force_run.  This will cause the appropriate
exception to be rethrown at the next QUIT check.

Another case is the try / catch in tui_getc() in tui-io.c.  The
existing catch swallows the exception.  I've added a catch for
'gdb_exception_forced_quit', which also swallows the exception,
but also sets sync_quit_force_run and calls set_quit_flag in
order to restart forced quit processing at the next QUIT check.
This is required because it isn't safe to throw into/through
readline.

Thanks to Pedro Alves for suggesting this idea.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=26761
---
 gdb/linux-fork.c | 13 +++++++++++++
 gdb/tui/tui-io.c |  9 +++++++++
 2 files changed, 22 insertions(+)

diff --git a/gdb/linux-fork.c b/gdb/linux-fork.c
index 61545b859ea..fc2f00d0766 100644
--- a/gdb/linux-fork.c
+++ b/gdb/linux-fork.c
@@ -430,6 +430,19 @@ class scoped_switch_fork_info
 	    fork_load_infrun_state (m_oldfp);
 	    insert_breakpoints ();
 	  }
+	catch (const gdb_exception_quit &ex)
+	  {
+	    /* We can't throw from a destructor, so re-set the quit flag
+	      for later QUIT checking.  */
+	    set_quit_flag ();
+	  }
+	catch (const gdb_exception_forced_quit &ex)
+	  {
+	    /* Like above, but (eventually) cause GDB to terminate by
+	       setting sync_quit_force_run.  */
+	    sync_quit_force_run = 1;
+	    set_quit_flag ();
+	  }
 	catch (const gdb_exception &ex)
 	  {
 	    warning (_("Couldn't restore checkpoint state in %s: %s"),
diff --git a/gdb/tui/tui-io.c b/gdb/tui/tui-io.c
index 2f39e34df2f..ac3c7296499 100644
--- a/gdb/tui/tui-io.c
+++ b/gdb/tui/tui-io.c
@@ -1275,6 +1275,15 @@ tui_getc (FILE *fp)
     {
       return tui_getc_1 (fp);
     }
+  catch (const gdb_exception_forced_quit &ex)
+    {
+      /* As noted below, it's not safe to let an exception escape
+         to newline, so, for this case,  reset the quit flag for
+	 later QUIT checking.  */
+      sync_quit_force_run = 1;
+      set_quit_flag ();
+      return 0;
+    }
   catch (const gdb_exception &ex)
     {
       /* Just in case, don't ever let an exception escape to readline.
-- 
2.34.3