[PATCH v6 4/4] [gdb/tui] Fix crash with debuginfod query (C-x C-a)

[Tom de Vries <tdevries@suse.de>]

PR tui/33794 reports an abort when the debuginfod query happens while enabling
TUI using the "C-x C-a" key combination.

The abort triggering is this one in rl_callback_read_char:
...
  if (rl_linefunc == NULL)
    {
      _rl_errmsg ("readline_callback_read_char() called with no handler!");
      abort ();
    }
...

This is similar to PR python/24796, and can be fixed by applying a similar fix
in tui_enable:
...
 void
 tui_enable (void)
 {
+  SCOPE_EXIT { reinstall_readline_callback_handler_cleanup (); };
...

After doing so, things seem to be fixed, but when compiling gdb with Asan, we
run into a heap-use-after-free.

The problem here is that readline is used recursively:
- readline is entered when handling the C-x C-a key combination
- readline is entered again when handling the debuginfod query

This would have to be addressed in readline, but in the mean time we need a
fix in gdb.

An RFC [1] was posted exploring the option of avoiding recursive readline use
by rather than handling the key combination directly, queueing it in an event
queue and handling the events later.

This patch takes a conservative approach: bail out if debuginfod enabled is
set to ask when entering TUI.

The fix is minimal, and consequently low-risk, and applies cleanly to the
gdb-17-branch (and that holds more or less as well for the patches this patch
is dependent on).

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33794

[1] https://sourceware.org/pipermail/gdb-patches/2026-February/225289.html
---
 gdb/testsuite/gdb.tui/query.exp |  3 +--
 gdb/tui/tui.c                   | 10 ++++++++--
 gdb/tui/tui.h                   |  2 +-
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/gdb/testsuite/gdb.tui/query.exp b/gdb/testsuite/gdb.tui/query.exp
index acf0db63ebb..eb0bee49aec 100644
--- a/gdb/testsuite/gdb.tui/query.exp
+++ b/gdb/testsuite/gdb.tui/query.exp
@@ -49,8 +49,7 @@ file delete $tmpfile
 
 set l {}
 lappend l "command"
-# Disabled due to PR33794.
-#lappend l "keys"
+lappend l "keys"
 
 foreach_with_prefix how $l {
     save_vars { env(DEBUGINFOD_URLS) } {
diff --git a/gdb/tui/tui.c b/gdb/tui/tui.c
index 9cf21f390c8..d2f1b79616c 100644
--- a/gdb/tui/tui.c
+++ b/gdb/tui/tui.c
@@ -41,6 +41,7 @@
 #include "top.h"
 #include "ui.h"
 #include "observable.h"
+#include "debuginfod-support.h"
 
 #include <fcntl.h>
 
@@ -140,7 +141,7 @@ tui_rl_switch_mode (int notused1 = 0, int notused2 = 0)
 
 	  /* If tui_enable throws, we'll re-prep below.  */
 	  rl_deprep_terminal ();
-	  tui_enable ();
+	  tui_enable (false);
 	}
     }
   catch (const gdb_exception_forced_quit &ex)
@@ -399,13 +400,18 @@ gdb_getenv_term (void)
    the gdb output, configures the readline to work in tui mode.
    When in curses mode, it does nothing.  */
 void
-tui_enable (void)
+tui_enable (bool queries_allowed)
 {
   TUI_SCOPED_DEBUG_ENTER_EXIT;
 
   if (tui_active)
     return;
 
+  if (!queries_allowed
+      && debuginfod_enabled_ask_p ()
+      && defaulted_query_auto_answers_p () != TRIBOOL_TRUE)
+    error (_("Please set debuginfod enabled to on or off before enabling TUI"));
+
   tui_batch_rendering defer;
 
   /* To avoid to initialize curses when gdb starts, there is a deferred
diff --git a/gdb/tui/tui.h b/gdb/tui/tui.h
index 7daefe2c9bb..e90c40b562e 100644
--- a/gdb/tui/tui.h
+++ b/gdb/tui/tui.h
@@ -70,7 +70,7 @@ extern bool tui_get_command_dimension (unsigned int *width,
 extern void tui_ensure_readline_initialized ();
 
 /* Enter in the tui mode (curses).  */
-extern void tui_enable (void);
+extern void tui_enable (bool queries_allowed = true);
 
 /* Leave the tui mode.  */
 extern void tui_disable (void);
-- 
2.51.0