Building EVL

Building EVL is a two-step process, which may happen in any order:

  • a Linux kernel image featuring the EVL core is built.

  • the EVL library (aka libevl), basic utilities and test programs are generated.

Prerequisites

We need:

  • a GCC toolchain for the target CPU architecture.

  • the UAPI headers from the target Linux kernel fit with the EVL core. Each UAPI file exports a set of definitions and interface types which are shared with libevl.so running in user-space, so that the latter can submit well-formed system calls to the former. In other words, to build libevl.so, we need access to the contents of include/uapi/asm/ and include/uapi/evl/ from a source kernel tree which contains the EVL core which is going to handle the system calls.

libevl relies on thread-local storage support (TLS), which might be broken in some obsolete toolchains.

Building the core

The kernel source tree which includes the latest EVL core is maintained at git://git.evlproject.org/linux-evl. The development branch is evl/master.

Once your favorite kernel configuration tool is brought up, you should see the EVL configuration block somewhere inside the General setup menu. This configuration block looks like this:

Alt text

Enabling CONFIG_EVL should be enough to get you started, the default values for other EVL settings are safe to use. You should make sure to have CONFIG_EVL_LATMUS and CONFIG_EVL_HECTIC enabled too; those are drivers required for running the latmus and hectic utilities available with libevl, which measure latency and validate the context switching sanity.

If you are unfamiliar with building kernels, this document may help.

Building libevl

Build command

The generic command for building libevl is:

$ make [-C $SRCDIR] [ARCH=$cpu_arch] [CROSS_COMPILE=$toolchain] UAPI=$uapi_dir [OTHER_BUILD_VARS] [goal...]

Main build variables

Variable Description
$SRCDIR Path to this source tree
$cpu_arch CPU architecture you build for (‘arm’, ‘arm64’)
$toolchain Optional prefix of the binutils filename (e.g. ‘aarch64-linux-gnu-’, ‘arm-linux-gnueabihf-’)

Other build variables

Variable Description Default
D={0|1} Disable or enable debug build, i.e. -g -O0 vs -O2 0
O=$output_dir Generate binary output files into $output_dir .
V={0|1} Set build verbosity level, 0 is terse 0
DESTDIR=$install_dir Install library and binaries into $install_dir /usr/evl

Make goals

Goal Action
all generate all binaries (library, utilities and tests)
clean remove the build files
install do all, copying the generated binaries to $DESTDIR in the process

Examples

Cross-compiling EVL

Let’s say the library source code is located at ~/git/libevl, and the kernel sources featuring the EVL core is located at ~/git/linux-evl.

This is good practice to always generate the build output files to a separate build directory using the O= directive on the make command line, not to clutter your source tree with those. Generating output to a separate directory also creates convenience Makefiles on the fly in the output tree, which you can use to run subsequent builds, without having to mention the whole series of settings on the make command line again.

Cross-compiling EVL and installing the resulting library and utilities to a staging directory located at /nfsroot/<machine>/usr/evl would amount to this:

Cross-compiling from a separate build directory

# First create a build directory the where output files should go
$ mkdir /tmp/build-imx6q && cd /tmp/build-imx6q
# Then start the build+install process
$ make -C ~/git/libevl O=$PWD ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- UAPI=~/git/linux-evl DESTDIR=/nfsroot/imx6q/usr/evl install

or,

Cross-compiling from the EVL library source tree

$ mkdir /tmp/build-hikey
$ cd ~/git/libevl
$ make O=/tmp/build-hikey ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- UAPI=~/git/linux-evl DESTDIR=/nfsroot/hikey/usr/evl install

Native EVL build

Conversely, you may want to build EVL natively on the target system. Installing the resulting library and utilities directly to their final home located at e.g. /usr/evl can be done as follows:

Building natively from a build directory

$ mkdir /tmp/build-native && cd /tmp/build-native
$ make -C ~/git/libevl O=$PWD UAPI=~/git/linux-evl DESTDIR=/usr/evl install

or,

Building natively from the EVL library source tree

$ mkdir /tmp/build-native
$ cd ~/git/libevl
$ make O=/tmp/build-native UAPI=~/git/linux-evl DESTDIR=/usr/evl install

Testing the installation

At this point, you really want to test the EVL installation.


Last modified: Sun, 23 Jun 2019 20:06:48 CEST