Avoid GDB SIGTTOU on catch exec + set follow-exec-mode new (PR 23368)

Here's a summary of PR 23368:

  #include <unistd.h>
  int main (void)
  {
    char *exec_args[] = { "/bin/ls", NULL };
    execve (exec_args[0], exec_args, NULL);
  }

$ gdb -nx t -ex "catch exec" -ex "set follow-exec-mode new" -ex run
...
[1]  + 13146 suspended (tty output)  gdb -q -nx t -ex "catch exec" -ex "set follow-exec-mode new" -ex run
$

Here's what happens: when the inferior execs with "follow-exec-mode
new", we first "mourn" it before creating the new one.  This ends up
calling inflow_inferior_exit, which sets the per-inferior terminal state
to "is_ours":

  inf->terminal_state = target_terminal_state::is_ours;

At this point, the inferior's terminal_state is is_ours, while the
"reality", tracked by gdb_tty_state, is is_inferior (GDB doesn't own the
terminal).

Later, we continue processing the exec inferior event and decide we want
to stop (because of the "catch exec") and call target_terminal::ours to
make sure we own the terminal.  However, we don't actually go to the
target backend to change the settings, because the core thinks that no
inferior owns the terminal (inf->terminal_state is
target_terminal_state::is_ours, as checked in
target_terminal_is_ours_kind, for both inferiors).  When something in
readline tries to mess with the terminal settings, it generates a
SIGTTOU.

This patch fixes this by tranferring the state of the terminal from the
old inferior to the new inferior.

gdb/ChangeLog:

	PR gdb/23368
	* infrun.c (follow_exec): In the follow_exec_mode_new case,
	transfer terminal state from old new new inferior.
	* terminal.h (swap_terminal_info): New function.
	* inflow.c (swap_terminal_info): New function.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 19a87f40fe1df6b3d320a90010ec6331b6772adc..5ef217d446c5a93492abc8d888709a40a89ff6b0 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2018-10-23  Simon Marchi  <simon.marchi@polymtl.ca>
+
+       PR gdb/23368
+       * infrun.c (follow_exec): In the follow_exec_mode_new case,
+       transfer terminal state from old new new inferior.
+       * terminal.h (swap_terminal_info): New function.
+       * inflow.c (swap_terminal_info): New function.
+
 2018-10-23  Tom Tromey  <tom@tromey.com>
 
        * record-btrace.c (get_thread_current_frame_id): Rename from

diff --git a/gdb/inflow.c b/gdb/inflow.c
index caff646207098c9938b43ccb671a39343c5ae910..a0c1c7d884a4a03a85852cb768b184fa5345b5a0 100644 (file)
--- a/gdb/inflow.c
+++ b/gdb/inflow.c
@@ -702,6 +702,22 @@ copy_terminal_info (struct inferior *to, struct inferior *from)
   to->terminal_state = from->terminal_state;
 }
 
+/* See terminal.h.  */
+
+void
+swap_terminal_info (inferior *a, inferior *b)
+{
+  terminal_info *info_a
+    = (terminal_info *) inferior_data (a, inflow_inferior_data);
+  terminal_info *info_b
+    = (terminal_info *) inferior_data (a, inflow_inferior_data);
+
+  set_inferior_data (a, inflow_inferior_data, info_b);
+  set_inferior_data (b, inflow_inferior_data, info_a);
+
+  std::swap (a->terminal_state, b->terminal_state);
+}
+
 void
 info_terminal_command (const char *arg, int from_tty)
 {

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 72e249617670987eee9893748afa2c7d3b159b8b..9473d1f20f62fd35e77dce071c8fd82f9488aa87 100644 (file)
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1189,12 +1189,14 @@ follow_exec (ptid_t ptid, char *exec_file_target)
       /* The user wants to keep the old inferior and program spaces
         around.  Create a new fresh one, and switch to it.  */
 
-      /* Do exit processing for the original inferior before adding
-        the new inferior so we don't have two active inferiors with
-        the same ptid, which can confuse find_inferior_ptid.  */
+      /* Do exit processing for the original inferior before setting the new
+        inferior's pid.  Having two inferiors with the same pid would confuse
+        find_inferior_p(t)id.  Transfer the terminal state and info from the
+         old to the new inferior.  */
+      inf = add_inferior_with_spaces ();
+      swap_terminal_info (inf, current_inferior ());
       exit_inferior_silent (current_inferior ());
 
-      inf = add_inferior_with_spaces ();
       inf->pid = pid;
       target_follow_exec (inf, exec_file_target);
 

diff --git a/gdb/terminal.h b/gdb/terminal.h
index 7774eefcd46ef755e41d7b5cccbaa89c4d987008..da27e46f6ec5f39b025ab6bc940bf5bd34564c5c 100644 (file)
--- a/gdb/terminal.h
+++ b/gdb/terminal.h
@@ -29,6 +29,9 @@ extern void new_tty_postfork (void);
 
 extern void copy_terminal_info (struct inferior *to, struct inferior *from);
 
+/* Exchange the terminal info and state between inferiors A and B.  */
+extern void swap_terminal_info (inferior *a, inferior *b);
+
 extern pid_t create_tty_session (void);
 
 /* Set up a serial structure describing standard input.  In inflow.c.  */