2018-08-06 23:37 GMT+09:00 Vasily Gorbik <gor@xxxxxxxxxxxxx>: > With kbuild there is no easy way to re-compile source files from another > directory, which is required for the decompressor on some platforms > (files like lib/ctype.c, lib/cmdline.c, etc). Writing custom build > rules for those files is not feasible since original rules are complex > and kbuild functions and variables are not exposed. > > The simplest solution is to reverse include source files either into > existing files or separate files. That eliminates the need to tackle > with the kbuild rules, but is ugly. > > Here is another solution to that problem, utilizing secondary expansion. > Build rules are in a form: > $(obj)/%.o: $(src)/%.c ... > $(obj)/%.o: $(src)/%.S ... > > "src" variable could be changed to cover the need of specifying alternate > source file directory. > src := $(if $(SRCDIR_$(@F)),$(SRCDIR_$(@F)),$(src)) > > So, if there is SRCDIR_<target> set, it will be used, original "src" is > used otherwise. But that wouldn't work as it is. To be able to utilize > automatic variables in implicit prerequisite secondary expansion has to > be used and src value has to be additionally escaped. > > Alternate src dir then could be specified in Makefile as: > obj-y := file1.o file2.o > SRCDIR_file1.o := file1/src/dir > SRCDIR_file2.o := file2/src/dir > > Which is enough to build $(obj)/file1.o from file1/src/dir/file1.(c|S), > and $(obj)/file2.o from file2/src/dir/file2.(c|S) Is this a simple solution compared with existing ones? Kind of. However, it is just moving the complexity around from Makefiles to the core build scripts, after all. I guess the increase of build time is not too big, ( 1 % or so for the incremental build of allmodconfig) but I do not like performing the second expansion for every directory to save some a few Makefiles. > Secondary expansion has been introduced with make 3.81, which is > minimal supported version by kbuild itself. > > Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx> > --- > scripts/Makefile.build | 26 +++++++++++++++----------- > 1 file changed, 15 insertions(+), 11 deletions(-) > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build > index 514ed63ff571..97c6ece96cfb 100644 > --- a/scripts/Makefile.build > +++ b/scripts/Makefile.build > @@ -70,6 +70,10 @@ $(warning kbuild: Makefile.build is included improperly) > endif > > # =========================================================================== > +# Allow to specify alternate source directory of target's implicit prerequisite > +# e.g. 'SRCDIR_cmdline.o := lib' This does not work for single targets. 'make foo/bar/cmdline.o' works, but 'make foo/bar/cmdline.i' does not. > +.SECONDEXPANSION: > +srcdir := $$(if $$(SRCDIR_$$(@F)),$$(SRCDIR_$$(@F)),$(src)) > -- Best Regards Masahiro Yamada -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
