Documentation/process/changes.rst notes the minimal GNU Make version,
but it is not checked anywhere.
We could check $(MAKE_VERSION), but another simple way is to check
$(.FEATURES) since the feature list always grows.
GNU Make 3.81 expands $(.FEATURES) to:
target-specific order-only second-expansion else-if archives jobserver check-symlink
GNU Make 3.82 expands $(.FEATURES) to:
target-specific order-only second-expansion else-if shortest-stem undefine archives jobserver check-symlink
To ensure Make >= 3.82, you can check either 'shortest-stem' or
'undefine'.
This way is not always possible. For example, Make 4.0 through 4.2 have
the same set of $(.FEATURES). At that point, we will need to come up
with a different approach.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
# Comments in this file are targeted only to the developer, do not
# expect to learn how to build the kernel reading this file.
+ifeq ($(filter undefine,$(.FEATURES)),)
+$(error GNU Make >= 3.82 is required. Your Make version is $(MAKE_VERSION))
+endif
+
$(if $(filter __%, $(MAKECMDGOALS)), \
$(error targets prefixed with '__' are only for internal use))