QEMU x86_64 -nographic full system breaks host Bash terminal line wrapping state after simulation ends, requires reset or "tput smam" to fix it

Bug #1857449 reported by Ciro Santilli 六四事件 法轮功 on 2019-12-24
This bug affects 1 person
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Bug Description

QEMU 4.2.0 compiled from source, Ubuntu 19.10, open a fresh new gnome terminal.

If you print 1000 = chars on the host terminal, then they do wrap around the end of the terminal:

printf "=%.0s" {0..1000}

However, if you first run QEMU:

x86_64-softmmu/qemu-system-x86_64 -nographic

and then quit it in any way, e.g. with Ctrl + A, and then re-run on the host terminal:

printf "=%.0s" {0..1000}

then the signs don't wrap around anymore, they just go "off the terminal to the right".

This can be fixed with either:

tpam smam

but unfortunately those don't work in tmux for some reason: https://github.com/tmux/tmux/issues/969

I consider this buggy behavior, QEMU should restore the original terminal state if possible.

Related: https://github.com/cirosantilli/linux-kernel-module-cheat/issues/110

Apparently the code you run (BIOS?) is sending the DECRST control sequence to the terminal, which disable the auto-wrap mode flag.
Looking at the detailed explanations on https://github.com/mattiase/wraptest I'm not sure how QEMU can save/restore this flag.

Ah, thanks for looking into this and identifying it to guest code Philippe. I don't know much about terminals, but yes, they are such archaic interfaces, maybe there is no API for it :-(

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