Wednesday, March 30, 2016

Build-testing for the Linux kernel DRM subsystem

Following up on this earlier post, I'll briefly detail how I run build tests on the Linux kernel DRM subsystem.

I maintain the scripts and build configurations in a git repository:


The build script takes a number of arguments, most of which should be familiar. You can get a list of them by running the scripts with the -h or --help option. Here's how I typically run the script:

 $ drm/build --jobs 13 --color  

This instructs the script to have make start 13 jobs (that's the number of cores * 2 + 1, feel free to use whatever you think is a good number) and colorize the output. I find colorized output convenient because it will mark failed builds with a bright red status report.

By default the script will derive the build directory name from the output of git describe and prepend build/ as well as append /drm. Each configuration will be built in a subdirectory (with the same name as the configuration) of that build directory. This should give you a fairly unique name, so no need to worry about losing any existing builds.

In addition to command-line options, the script can take a list of configurations to build via positional arguments.

Once done, each configuration's build directory contains a build.log file as well as an error.log file. The contents of error.log are included in the build.log file. In addition the script will output a single line per build, along with a status report of the build result.


There's another script in the above-mentioned repository: coverage. You can run it after a run of the build script to check for compile coverage. This is fairly simplistic, since it checks only on a per-file basis, not how much code in the file actually got compiled. It'll report any source files that aren't compiled in the drivers/gpu/drm directory and can be a quick indicator of whether or not the configurations are adequate.


Most of the above can be achieved by simply building x86 defconfig and ARM multi_v7_defconfig configurations. However there are drivers that aren't covered by those configurations (drm/vc4 needs ARM v6, EDIT: this is no longer true, ARCH_BCM2835 which DRM_VC4 depends on is now available with ARM v7 and hence multi_v7_defconfig) and the default configurations usually take much longer to build than the minimal configurations contained in the repository. Also the included configurations build 32-bit and 64-bit variants, which occasionally catches inconsistent type usage (size_t vs. unsigned long/int, ...).

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