Messages in this thread | | | Date | Fri, 09 Sep 2011 14:30:56 +0200 | From | Michal Marek <> | Subject | Re: [RFC] Kbuild: allow code re-use across different directories |
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On 20.8.2011 02:37, Arnaud Lacombe wrote: > Hi folks, > > The attached patch modify Kbuild to allow to directly re-use code in multiple > directory without having to go through a copy. Technically, it changes Kbuild to > use by default the VPATH feature of GNU make and provides accessors for Makefile > to change it indirectly. > > Considering: > > arch/foo/lib: > fancy.c > > We want to be able to build it with -DPANTS=32 in the kernel, but the > bootloader requires -DPANTS_SIZE=30. > > Currently we would do, either: > > arch/foo/lib/Makefile > LDFLAGS_fancy.o := -DPANTS=32 > obj-y += fancy.o > > and, either: > > arch/foo/boot/Makefile: > LDFLAGS_fancy.o := -DPANTS=30 > obj-y += fancy.o > $(obj)/fancy.c: $(srctree)/arch/foo/lib/fancy.c > $(call cmd,shipped) > > or > > arch/foo/boot/Makefile: > LDFLAGS_fancy.o := -DPANTS=30 > obj-y += fancy.o > $(obj)/fancy.o: $(srctree)/arch/foo/lib/fancy.c > $(call cmd,cc_c_o) > > The former implies an extra copy of the source file, the latter expose Kbuild > internal function. > > With the attached patch, we would do: > > arch/foo/boot/Makefile: > LDFLAGS_fancy.o := -DPANTS=30 > obj-y += fancy.o > vpath-y += $(srctree)/arch/foo/lib > > and let GNU make do the job.
I like this. The only issue I can think of right now, is that if you add a large directory to vpath-y, then it would be easy to accidentally reuse more files from that directory than intended. But that could be easily prevented by isolating those reusable source files.
Michal
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