XShmGetImage returns junk/garbage in between monitors

[Nicholas Wilson]

In xserver 1.14.3-3ubuntu2, we've observed that on multimonitor systems, we are passed garbage when grabbing the pixels that are not on any monitor.

This does not appear to be a bug in our application - it can be easily reproduced by taking a screenshot of the whole screen using GIMP on Ubuntu 13.10 beta.

The issue is not present in 1.13.3 as shipped in Ubuntu 13.04.

What we are doing: get the geometry of the root window (XGetGeometry), create a pixbuf of the same size (XShmCreateImage/XShmAttach). Then we try and grab the whole thing using XShmGetImage.

On multimonitor systems, the off-monitor portions are filling in the pixbuf with garbage (or garbled portions of other sections of the screen). That is, the monitors themselves are captured fine, but if the second monitor is smaller than the first, we used to get a black box in the dead space, where now we're getting garbage.

I'm trying to track down the source of the regression - a random stab in the dark might be f21cc327a56e3b453cf0dba04457223d61c27ea6? Alternatively, it may not be a bug in upstream at all - I haven't yet looked into the huge patchset Ubuntu's currently maintaining. Ubuntu's "-3ubuntu2 patchset is far larger than the git diff between 1.13.3 and 1.14.3!

[Nicholas Wilson (i-nicholas)]

Screenshot attached.

[Nicholas Wilson (i-nicholas)]

We've found the problem in Fedora 19 too, and reported it upstream.

https://bugs.freedesktop.org/show_bug.cgi?id=70801

[penalvch (penalvch)]

Nicholas Wilson, this bug was reported a while ago and there hasn't been any activity in it recently. We were wondering if this is still an issue? If so, could you please test for this with the latest development release of Ubuntu? ISO images are available from http://cdimage.ubuntu.com/daily-live/current/ .

If it remains an issue, could you please run the following command in the development release from a Terminal (Applications->Accessories->Terminal), as it will automatically gather and attach updated debug information to this report:

apport-collect -p xorg-server REPLACE-WITH-BUG-NUMBER

Please note, given that the information from the prior release is already available, doing this on a release prior to the development one would not be helpful.

Thank you for your understanding.

Helpful bug reporting tips:
https://wiki.ubuntu.com/ReportingBugs

[Paul White (paulw2u)]

Ubuntu 13.10 (saucy) reached end-of-life on July 17, 2014.

Re comment #2, the upstream issue was moved to:
https://gitlab.freedesktop.org/xorg/xserver/-/issues/449
but there has been no activity since the original report
in 2013.

There was no response to the request for apport information
in comment #3 so this issue has sat incomplete for over
eight years and did not expire due to the bug watch.