Cross compile QT with xcb, Feature 'xkbcommon' was enabled, but the pre-condition 'libs.xkbcommon' failed

SanZ

Hi,

I am trying to cross compile QT on Ubuntu 20.04, targeting an ARM chip, the toolchain is a OpenWRT-based one.

The build was fine with -no-xcb configure option. However when I try to enable xcb, I get the errors:

ERROR: Feature 'xkbcommon' was enabled, but the pre-condition 'libs.xkbcommon' failed.
ERROR: Feature 'xcb' was enabled, but the pre-condition 'features.thread && features.xkbcommon && libs.xcb' failed.

I see that most people get the second error, but not a lot of people get the first one, and fewer in cross compiling. I have installed
"sudo apt-get install '^libxcb.*-dev' libx11-xcb-dev libglu1-mesa-dev libxrender-dev libxi-dev libxkbcommon-dev libxkbcommon-x11-dev"
But it did not help, I guess it's because I'm cross compiling.

In my verbose log I see:
/path/to/pkg-config --exists --silence-errors xkbcommon '>=' 0.5.0
pkg-config did not find package.
=> source produced no result.
Trying source 1 (type inline) of library xkbcommon ...
None of [libxkbcommon.so libxkbcommon.a] found in [] and global paths.
=> source produced no result.

I also noticed that the libxkbcommon has been removed from qtbase source tree. So my question to start is: would I have to build libxkbcommon myself with my toolchain? Because I assume the ones I can find under /usr/lib won't do as they're for either i386 or x86_64, not ARM.

JKSH

@SanZ said in Cross compile QT with xcb, Feature 'xkbcommon' was enabled, but the pre-condition 'libs.xkbcommon' failed:

Also, I have a bunch of -skip options in my configure, maybe one of them stopped xcb from being configured/built?

I don't think so. XCB support only depends on the system's XCB and other graphical libraries. It doesn't depend on other Qt modules (whereas -skip only disables Qt modules)

Check the output of your configuration script (I believe you'll have a file called configure.summary) -- it should list what components are found or not found.

It seems that -qt-xcb option was removed from 5.12.1 onward?

Yes, it was removed in recent versions of Qt, for 2 reasons:

Security: It is safer for users to link to the latest XCB libraries than to use an old, bundled version
Maintenance: It takes up resources for Qt to keep updating and patching its own copy of XCB

As @ChrisW67 said, use your toolchain to cross-compile XCB first, then cross-compile Qt.

ChrisW67

You will need the library suitable for linking in your target environment, and you will probably have to build it (and any dependencies) yourself.

SanZ

Thank you Chris. That's what I was afraid of... But it doesn't make sense to me that QT would make it so difficult for people to cross compile this xcb platform plugin as I read somewhere else on this forum that the cross compile was fine with QT5.10.1 ...

SanZ

Some additional notes after a bit more search...

It seems that -qt-xcb option was removed from 5.12.1 onward? I am using 5.12.11, and when I try to remove -qt-xcb, the build is OK but does not generate libqxcb.so which is what I needed in the first place.

Also, I have a bunch of -skip options in my configure, maybe one of them stopped xcb from being configured/built? Is there a documentation somewhere on what -skip or -no-feature options would disable what components?

JKSH