Implicit rules cannot invoke other implicit rules

[DelilahHoare]

If an implicit rule has an input that does not yet exist but could be made by another implicit rule, it will be skipped.

all: test.a

%.a: %.b
	echo $< > $@

%.b:
	echo $* > $@

This test makefile will successfully create test.a when run by GNU make, but ckati will fail with No rule to make target 'test.a' due to the pattern being declined because test.b does not already exist.

[lberki]

Is this something required to build the Linux kernel?

[DelilahHoare]

Yes. Without this feature the build fails with No rule to make target 'arch/x86/entry/vdso/vdso-image-64.o'. The rule it should be using, $(obj)/vdso-image-%.c, takes $(obj)/vdso%.so as input, which should be built by the rule for $(obj)/%.so.