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Emacs terminal corruption in Debian virtualbox guests



Hello,

I have encountered a situation where I observe terminal corruption when using emacs (either emacs-nox or emacs -nw). The corruption can be demonstrated easily using isearch-forward for a single character which appears multiple times in the current buffer, and repeatedly searching to cause a wrap back around to the start.

Most commonly, the corruption involves the majority of the terminal undergo a linefeed, but with dynamically highlighted sections being rendered in the correct absolute location on the terminal. Less often, the corruption is limited to the text in the minibuffer alone. A complete buffer redraw (C-l) shows that the buffer contents is correct, and this temporally resolves the corruption.

I have several baremetal Debian systems (6, 7 and 8) and 3 Debian systems (7, 8, 8 with no desktop) as virtualbox guests on my laptop (windows sadly). All 64bit.

Each of the virtuabox guests have absolutely no terminal corruption when emacs is run from a real terminal (tty1,2,etc) but exhibit the corruption when run from a pseudo terminal. The baremetal systems show no corruption at all, even in pseudo terminals.

Corruption on the ptys occur in all cases I can construct; console emulators (including gnome-termainal, mate-terminal, xfce-terminal, and plain xterm), sshing in from outside, or being on a tty and running emacs inside screen.

I have experimented in various ways by trying to make the environments identical (as reported by `env`), making the tty setttings identical (as reported by `stty -a`), and even by copying the 'good' (baremetal) xterm terminfo and using strace to verify that the new terminfo is being loaded. In addition, I have tried with and without virtualbox guest utilities.

I was able to control one difference. using TERM=linux in a pty (to match TERM= in a tty) removes the linefeed corruption, but still leaves corruption in the minibuffer when the amount of text would reduce. Is it possible that all the corruption is just an issue with blanking the terminal, or subportions thereof?

This does not obvious appear to be a bug with emacs itself (23 or 24), or anything about a particular version of Debian (both 7 and 8 affected equally, with 3.2 and 3.13 kernels respectively). The only common factor is pseudo terminals inside virtualbox guests, which is quite strange.

I am now out of ideas to continue. Does anyone have any suggestions for what this issue might be, or how I can debug the issue further?

Thanks in advance,

~Andrew


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