Re: [RFC] Kbuild: allow code re-use across different directories

[Arnaud Lacombe <lacombar@gmail.com>]

Hi,

On Fri, Aug 19, 2011 at 8:37 PM, Arnaud Lacombe <lacombar@gmail.com> 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.
>
Nicolas, I guess you were the one who was interested for a generic way
to do such code re-use, did you had any chance to test the quoted
patch ?

Thanks,
 - Arnaud


> Comments welcome,
>  - Arnaud
>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
>
> ---
>  Makefile               |    5 +++--
>  scripts/Makefile.build |   24 +++++++++++++++---------
>  scripts/Makefile.lib   |   17 ++++++++++++-----
>  3 files changed, 30 insertions(+), 16 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index b4ca4e1..db7f7f5 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -154,9 +154,10 @@ objtree            := $(CURDIR)
>  src            := $(srctree)
>  obj            := $(objtree)
>
> -VPATH          := $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))
> +KBUILD_VPATH   := $(srctree)$(if $(KBUILD_EXTMOD),:$(KBUILD_EXTMOD))
> +VPATH          := $(KBUILD_VPATH)
>
> -export srctree objtree VPATH
> +export srctree objtree KBUILD_VPATH
>
>
>  # SUBARCH tells the usermode build what the underlying arch is.  That is set
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index a0fd502..ac539d7 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -18,6 +18,8 @@ always :=
>  targets :=
>  subdir-y :=
>  subdir-m :=
> +vpath-y :=
> +vpath-m :=
>  EXTRA_AFLAGS   :=
>  EXTRA_CFLAGS   :=
>  EXTRA_CPPFLAGS :=
> @@ -37,6 +39,7 @@ include scripts/Kbuild.include
>
>  # For backward compatibility check that these variables do not change
>  save-cflags := $(CFLAGS)
> +save-vpath := $(VPATH)
>
>  # The filename Kbuild has precedence over Makefile
>  kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
> @@ -48,6 +51,9 @@ ifeq ($(KBUILD_NOPEDANTIC),)
>         ifneq ("$(save-cflags)","$(CFLAGS)")
>                 $(error CFLAGS was changed in "$(kbuild-file)". Fix it to use EXTRA_CFLAGS)
>         endif
> +        ifneq ("$(save-vpath)","$(VPATH)")
> +                $(error VPATH was changed in "$(kbuild-file)". Please uses vpath-y)
> +        endif
>  endif
>
>  #
> @@ -198,13 +204,13 @@ $(multi-objs-y:.o=.lst) : modname = $(modname-multi)
>  quiet_cmd_cc_s_c = CC $(quiet_modtag)  $@
>  cmd_cc_s_c       = $(CC) $(c_flags) -fverbose-asm -S -o $@ $<
>
> -$(obj)/%.s: $(src)/%.c FORCE
> +$(obj)/%.s: %.c FORCE
>        $(call if_changed_dep,cc_s_c)
>
>  quiet_cmd_cc_i_c = CPP $(quiet_modtag) $@
>  cmd_cc_i_c       = $(CPP) $(c_flags)   -o $@ $<
>
> -$(obj)/%.i: $(src)/%.c FORCE
> +$(obj)/%.i: %.c FORCE
>        $(call if_changed_dep,cc_i_c)
>
>  cmd_gensymtypes =                                                           \
> @@ -219,7 +225,7 @@ cmd_cc_symtypes_c =                                                         \
>     $(call cmd_gensymtypes,true,$@) >/dev/null;                             \
>     test -s $@ || rm -f $@
>
> -$(obj)/%.symtypes : $(src)/%.c FORCE
> +$(obj)/%.symtypes : %.c FORCE
>        $(call cmd,cc_symtypes_c)
>
>  # C (.c) files
> @@ -301,13 +307,13 @@ define rule_cc_o_c
>  endef
>
>  # Built-in and composite module parts
> -$(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
> +$(obj)/%.o: %.c $(recordmcount_source) FORCE
>        $(call cmd,force_checksrc)
>        $(call if_changed_rule,cc_o_c)
>
>  # Single-part modules are special since we need to mark them in $(MODVERDIR)
>
> -$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
> +$(single-used-m): %.o: %.c $(recordmcount_source) FORCE
>        $(call cmd,force_checksrc)
>        $(call if_changed_rule,cc_o_c)
>        @{ echo $(@:.o=.ko); echo $@; } > $(MODVERDIR)/$(@F:.o=.mod)
> @@ -317,7 +323,7 @@ quiet_cmd_cc_lst_c = MKLST   $@
>                     $(CONFIG_SHELL) $(srctree)/scripts/makelst $*.o \
>                                     System.map $(OBJDUMP) > $@
>
> -$(obj)/%.lst: $(src)/%.c FORCE
> +$(obj)/%.lst: %.c FORCE
>        $(call if_changed_dep,cc_lst_c)
>
>  # Compile assembler sources (.S)
> @@ -331,13 +337,13 @@ $(real-objs-m:.o=.s): modkern_aflags := $(KBUILD_AFLAGS_MODULE) $(AFLAGS_MODULE)
>  quiet_cmd_as_s_S = CPP $(quiet_modtag) $@
>  cmd_as_s_S       = $(CPP) $(a_flags)   -o $@ $<
>
> -$(obj)/%.s: $(src)/%.S FORCE
> +$(obj)/%.s: %.S FORCE
>        $(call if_changed_dep,as_s_S)
>
>  quiet_cmd_as_o_S = AS $(quiet_modtag)  $@
>  cmd_as_o_S       = $(CC) $(a_flags) -c -o $@ $<
>
> -$(obj)/%.o: $(src)/%.S FORCE
> +$(obj)/%.o: %.S FORCE
>        $(call if_changed_dep,as_o_S)
>
>  targets += $(real-objs-y) $(real-objs-m) $(lib-y)
> @@ -349,7 +355,7 @@ quiet_cmd_cpp_lds_S = LDS     $@
>       cmd_cpp_lds_S = $(CPP) $(cpp_flags) -P -C -U$(ARCH) \
>                             -D__ASSEMBLY__ -DLINKER_SCRIPT -o $@ $<
>
> -$(obj)/%.lds: $(src)/%.lds.S FORCE
> +$(obj)/%.lds: %.lds.S FORCE
>        $(call if_changed_dep,cpp_lds_S)
>
>  # Build the compiled-in targets
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index aeea84a..b57b621 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -46,6 +46,13 @@ obj-m                := $(filter-out %/, $(obj-m))
>
>  subdir-ym      := $(sort $(subdir-y) $(subdir-m))
>
> +#
> +vpath-ym       := $(vpath-y) $(vpath-m)
> +VPATH          := $(KBUILD_VPATH)
> +VPATH          += $(srctree)/$(src)
> +VPATH          += $(obj)
> +VPATH          += $(vpath-ym)
> +
>  # if $(foo-objs) exists, foo.o is a composite object
>  multi-used-y := $(sort $(foreach m,$(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
>  multi-used-m := $(sort $(foreach m,$(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
> @@ -167,7 +174,7 @@ ifdef REGENERATE_PARSERS
>  quiet_cmd_gperf = GPERF $@
>       cmd_gperf = gperf -t --output-file $@ -a -C -E -g -k 1,3,$$ -p -t $<
>
> -$(src)/%.hash.c_shipped: $(src)/%.gperf
> +$(src)/%.hash.c_shipped: %.gperf
>        $(call cmd,gperf)
>
>  # LEX
> @@ -177,7 +184,7 @@ LEX_PREFIX = $(if $(LEX_PREFIX_${baseprereq}),$(LEX_PREFIX_${baseprereq}),yy)
>  quiet_cmd_flex = LEX     $@
>       cmd_flex = flex -o$@ -L -P $(LEX_PREFIX) $<
>
> -$(src)/%.lex.c_shipped: $(src)/%.l
> +$(src)/%.lex.c_shipped: %.l
>        $(call cmd,flex)
>
>  # YACC
> @@ -187,13 +194,13 @@ YACC_PREFIX = $(if $(YACC_PREFIX_${baseprereq}),$(YACC_PREFIX_${baseprereq}),yy)
>  quiet_cmd_bison = YACC    $@
>       cmd_bison = bison -o$@ -t -l -p $(YACC_PREFIX) $<
>
> -$(src)/%.tab.c_shipped: $(src)/%.y
> +$(src)/%.tab.c_shipped: %.y
>        $(call cmd,bison)
>
>  quiet_cmd_bison_h = YACC    $@
>       cmd_bison_h = bison -o/dev/null --defines=$@ -t -l -p $(YACC_PREFIX) $<
>
> -$(src)/%.tab.h_shipped: $(src)/%.y
> +$(src)/%.tab.h_shipped: %.y
>        $(call cmd,bison_h)
>
>  endif
> @@ -204,7 +211,7 @@ endif
>  quiet_cmd_shipped = SHIPPED $@
>  cmd_shipped = cat $< > $@
>
> -$(obj)/%: $(src)/%_shipped
> +$(obj)/%: %_shipped
>        $(call cmd,shipped)
>
>  # Commands useful for building a boot image
> --
> 1.7.6.153.g78432
>
>