Makefile: Introduce LIBFDT_DIR to specify libfdt location

The arm, arm64, powerpc and riscv architectures require that libfdt is
installed on the system, however the library might not be available for
every architecture on the user's distro of choice. Or the static version of
the library, needed for the lkvm-static target, might be missing.
Fortunately, kvmtool has anticipated this situation and it includes
instructions to compile and install libfdt in the INSTALL file.
Unfortunately, those instructions do not always work (for example, because
the user is missing the needed permisssions), leaving the user unable to
compile kvmtool.

As an alternative to installing libfdt system-wide, provide the
LIBFDT_DIR variable when compiling kvmtool. For example, when compiling
with the command:

$ make ARCH=<arch> CROSS_COMPILE=<cross_compile> LIBFDT_DIR=<dir>

kvmtool will link the executable against the static version of the library
located in LIBFDT_DIR/libfdt.a.

LIBFDT_DIR takes precedence over the system library, as there are valid
reasons to prefer a self-compiled library over the one that the distro
provides (like the system library being older).

Note that this will slightly increase the size of the executable. For the
arm64 architecture, the increase has been measured to be about 100KB, or
about 5% of the total executable size.

Signed-off-by: Alexandru Elisei <>
Signed-off-by: Will Deacon <>
2 files changed