使用自动工具的动态目标

Question

I am trying to achieve something very specific with autotools - dynamic variable names. My goal is to create dynamic targets depending on a certain configuration file, similarly to the Linux kernel.

The Linux kernel can be configured using make menuconfig, which eventually generates a .config. The Makefiles of the Linux kernel contain targets such as obj-$(CONFIG_DMA) and depending on the value of CONFIG_DMA (y, n or m) , the associated source file will be built in statically, as a module, or not at all. I am using kconfig-frontends which lets me generate a .config file which I can then include in a standard GNU Makefile and use successfully onwards. I would like to achieve the same level of functionality with automake, but unfortunately automake refuses to set variable names depending on an external environment variable. I can think of hacky ways to get around this issue, but I'm sure there must be a way to achieve this in a clear fashion. Can anyone think of a solution for this?

Any help is appreciated, and I'm open to using cmake if it solves my problem.

Thanks!

Answer 1

Perhaps you can use EXTRA_foo_SOURCES ? You might not be able to use variable substitution in the LHS of a variable assignment, but you certainly can do so on the RHS. List all possible sources in EXTRA_foo_SOURCES , and then, based on what the .config defines, set foo_SOURCES - and consider using += for doing to.

You may have to invent a filename extension convention to get the different behaviour you want based on y/m/n; perhaps foo_SOURCES = mod.yo for a built-in module (and don't let *.o for a *_SOURCES* variable distract you - just provide the rules and make should figure it out), foo_SOURCES = mod.mo for a loadable module, and foo_SOURCES = mod.no for a disabled module. Then you need to help make glue the rules together. Something to give you some ideas:

-include .config
EXTRA_foo_SOURCES = $(obj-y) $(obj-m)
.c.o: # No rule; disables implicit rule
.c.yo:
    $(COMPILE) -o $@ $<
.c.mo:
    $(COMPILE) -DTHIS_IS_A_MODULE -o $@ $<
.c.no:
    touch $@
.yo.o:
    cp $< $@
.mo.o:
    cp $< $@
.no.o:
    cp /path/to/null/object.o $@

Hope you can make something of this. I present this as a soup of automake atoms, not as a finished product, in the hope that you can turn it into a beautiful molecule.