When using gdb -i=mi to debug a program, I typically split the window into two buffers vertically. But every time my program prints something gud automatically replaces my source code buffer with I/O buffer and pops up a new "frame" that contains my source code, and what's worse is that it creates a "dedicated window" that I can't switch back to source code. This behavior is obviously very very annoying, it should for example, open a new frame for the I/O buffer instead. How can I achieve that or just simply turn off auto replacing buffer for gud? (gud-gdb doesn't seem to have such behaviors but it doesn't show where breakpoints are)

  • I disabled (by commenting out) all references to setting a window dedicated with a t, and I removed/replaced the ACTION argument for display-buffer within gud-display-line to nil. I'm sorry that I don't have a fancy advice and I realize that is blasphemy to modify the source code. I set gdb-display-buffer-other-frame-action to my own custom function '(my-custom-function), but I'm presently not using that feature. I essentially wanted just two windows -- one window with the gdb debugger, and the other window gets the source-code.
    – lawlist
    Commented Dec 3, 2017 at 4:01
  • blasphemy continued: Within gdb-display-buffer, I commented out (set-window-dedicated-p window t). Within gdb-set-window-buffer, I commented out (set-window-dedicated-p window t). Then, I typed: M-x byte-compile-file. You could also create new functions instead and use things like defalias to replace your new function, or you could just require the source-code libraries in your init.el or .emacs before redefining the functions using the same name. I think the author liked having many windows and frames instead of just 2 windows on the selected frame.
    – lawlist
    Commented Dec 3, 2017 at 4:15
  • With regards to showing breakpoints, the code includes visual indicators in the fringe identifying the breakpoints. However, I haven't used those features yet. Today, is coincidentally the first time I have used these libraries and spent quite a bit of time implementing my own bug-fixes and setting up my desired behavior. If after you resolve the window display issue and you still don't see the breakpoints indicated with fringe indicators in the source-code buffer, then please consider posting a new question on that specific issue and try M-x eval-expression RET (display-images-p) RET.
    – lawlist
    Commented Dec 3, 2017 at 4:30

2 Answers 2


The automatic pop-up of the i/o buffer can be disabled by setting gdb-display-io-nopopup to t. In your .emacs file, add:

;; Prevent gdb from popping i/o window to the foreground on every output op
(setq-default gdb-display-io-nopopup t)

I learned this from ajp's answer here.

  • Can you add a snippet that should be added to the init file to make your answer easier to follow for novices?
    – user12563
    Commented May 2, 2019 at 19:29
  • That does work. How come none of us involved in this question didn't know that answer existed! Commented May 3, 2019 at 5:56
  • 1
    @DoMiNeLa10: Done. Commented May 10, 2019 at 18:39
  • @MinghengWang: I wish I knew. I've been struggling with this problem for years before I stumbled on ajp's answer after the nth search. Commented May 10, 2019 at 18:41

A partial answer is to disable gud from making the windows "dedicated", so you can change their buffer. From https://www.emacswiki.org/emacs/GDB-MI:

;; Force gdb-mi to not dedicate any windows
(advice-add 'gdb-display-buffer
        :around (lambda (orig-fun &rest r)
              (let ((window (apply orig-fun r)))
            (set-window-dedicated-p window nil)

(advice-add 'gdb-set-window-buffer
        :around (lambda (orig-fun name &optional ignore-dedicated window)
              (funcall orig-fun name ignore-dedicated window)
              (set-window-dedicated-p window nil)))

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