Using the Build System

L4Re uses make for building all artifacts of the system.

While it is always safe and valid to just issue make from the root directory of your build tree, this takes longer than needed when building everything is not required. For example, this is the case if you are working on a specific package.

There are a couple of options to only build what is of interest.

Build specific packages only

You can build a specific package only, including its dependencies, like this from the root of your build tree:

build-root-dir$ make pkg/l4re-core/moe

This builds moe including all of moe’s dependencies only.

If you just want to build a package, not considering its dependencies, just do:

build-root-dir$ make -C pkg/l4re-core/moe

In fact that works with any directory.

This is useful if you are working on a specific package and just want to recompile this specific code.

The build system also has a shortcut for building multiple directories at once like with make’s -C. For example, if you are working on a library and need to build the library as well as the program using it, you can do:

build-root-dir$ make S=pkg/mylib/lib/src:pkg/myprog

This will just build those two directories.

Building from the source tree

If you build from the source tree, you need to specify the root of the object tree, do this with O=:

source-tree$ make O=/path/to/obj-tree

Build Anywhere

The L4Re build system has Makefiles everywhere, so you can also start the build process from everywhere. This includes both the source tree as well as the object tree. The build system will descent to sub-directories.

Parallel Building

make uses the -j parameter with a number indicating the parallelism it should use. So using make -j8 is a good choice if you happen to have an 8 core machine.

To avoid mixing output of different packages but still benefit from parallel builds of individual object files of a package, parallel building can be enabled with the PL= option. Call make without -j like this:

$ make PL=8

Building Intermediate Files

Within the OBJ-* directories in the build tree, intermediate .i pre-processed files and .S assembly files can be generated, like this:

pkg/l4re-core/moe/server/src/OBJ-arm64_armv8a-std-l4f$ make main.i
pkg/l4re-core/moe/server/src/OBJ-arm64_armv8a-std-l4f$ make main.S

Inspecting Disassembly

Sometimes it is useful to look at the disassembly of a program. There is a shortcut for this:

pkg/l4re-core/moe/server/src/OBJ-arm64_armv8a-std-l4f$ make disasm

For directories with multiple targets this will automatically disassemble the first. Specify DABIN to choose another one in these instances. For example to disassemble liblua.so instead of liblua.a use:

pkg/l4re-core/lua/lib/build/OBJ-arm64_armv8a-std-l4f$ make disasm DABIN=liblua.so