[gdb/tui] Fix resizing of terminal to 1 or 2 lines

When starting TUI in a terminal with 3 lines:
...
$ echo $LINES
3
$ gdb -q -tui
...
and resizing the terminal to 2 lines we run into a segfault.

The problem is that for the source window:
- the minimum height is 3 (the default), but
- the maximum height is only 2 because there are only 2 lines.

This discrepancy eventually leads to a call to newwin in make_window with:
...
(gdb) p height
$1 = 3
(gdb) p width
$2 = 56
(gdb) p y
$3 = -1
(gdb) p x
$4 = 0
...
which results in a nullptr.

This violates the assumption here in tui_apply_current_layout:
....
  /* Get the new list of currently visible windows.  */
  std::vector<tui_win_info *> new_tui_windows;
  applied_layout->get_windows (&new_tui_windows);
...
that get_windows only returns visible windows, which leads to tui_windows
holding a dangling pointer, which results in the segfault.

Fix this by:
- making sure get_windows only returns visible windows, and
- detecting the situation and dropping windows from the layout if
  there's no room for them.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

PR tui/31044
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31044

1 files changed, 9 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.tui/resize.exp b/gdb/testsuite/gdb.tui/resize.exp
index 60d5116..e15f8a2 100644
--- a/gdb/testsuite/gdb.tui/resize.exp
+++ b/gdb/testsuite/gdb.tui/resize.exp
@@ -39,3 +39,12 @@ Term::check_contents "source at startup" "\\|.*21 *return 0"
 
 Term::resize 40 90
 Term::check_box "source box after resize" 0 0 90 26
+
+# Check that resizing to less than 3 lines doesn't cause problems.
+foreach lines { 2 1 } {
+    with_test_prefix lines=$lines {
+	Term::resize $lines 90 0
+	Term::wait_for ""
+	Term::check_region_contents "has prompt" 0 0 90 $lines "$gdb_prompt"
+    }
+}