Re: [PATCH v3 bpf-next 07/14] samples: bpf: add makefile.target for separate CC target build

[Ivan Khoronzhuk]

On Tue, Sep 17, 2019 at 04:19:40PM -0700, Andrii Nakryiko wrote:
> On Mon, Sep 16, 2019 at 3:58 AM Ivan Khoronzhuk
> <ivan.khoronzhuk@xxxxxxxxxx> wrote:
> > The makefile.target is added only and will be used in
>
> typo: Makefile
>
> > sample/bpf/Makefile later in order to switch cross-compiling on CC
>
> on -> to
>
> > from HOSTCC environment.
> >
> > The HOSTCC is supposed to build binaries and tools running on the host
> > afterwards, in order to simplify build or so, like "fixdep" or else.
> > In case of cross compiling "fixdep" is executed on host when the rest
> > samples should run on target arch. In order to build binaries for
> > target arch with CC and tools running on host with HOSTCC, lets add
> > Makefile.target for simplicity, having definition and routines similar
> > to ones, used in script/Makefile.host. This allows later add
> > cross-compilation to samples/bpf with minimum changes.
> >
> > The tprog stands for target programs built with CC.
>
> Why tprog? Could we just use prog: hostprog vs prog.
Prev. version was with prog, but Yonghong Song found it ambiguous.
As prog can be bpf also. So, decision was made to follow logic:
* target prog - non bpf progs
* bpf prog = bpf prog, that can be later smth similar, providing build options
 for each bpf object separately.

Details here:
https://lkml.org/lkml/2019/9/13/1037

> > Makefile.target contains only stuff needed for samples/bpf, potentially
> > can be reused later and now needed only for unblocking tricky
> > samples/bpf cross compilation.
> >
> > Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
> > ---
> >  samples/bpf/Makefile.target | 75 +++++++++++++++++++++++++++++++++++++
> >  1 file changed, 75 insertions(+)
> >  create mode 100644 samples/bpf/Makefile.target
> >
> > diff --git a/samples/bpf/Makefile.target b/samples/bpf/Makefile.target
> > new file mode 100644
> > index 000000000000..fb6de63f7d2f
> > --- /dev/null
> > +++ b/samples/bpf/Makefile.target
> > @@ -0,0 +1,75 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +# ==========================================================================
> > +# Building binaries on the host system
> > +# Binaries are not used during the compilation of the kernel, and intendent
>
> typo: intended
>
> > +# to be build for target board, target board can be host ofc. Added to build
>
> What's ofc, is it "of course"?
yes, ofc )

> > +# binaries to run not on host system.
> > +#
> > +# Sample syntax (see Documentation/kbuild/makefiles.rst for reference)
> > +# tprogs-y := xsk_example
> > +# Will compile xdpsock_example.c and create an executable named xsk_example
>
> You mix references to xsk_example and xdpsock_example, which is very
> confusing. I'm guessing you meant to use xdpsock_example consistently.
Oh, yes. Thanks.

> > +#
> > +# tprogs-y    := xdpsock
> > +# xdpsock-objs := xdpsock_1.o xdpsock_2.o
> > +# Will compile xdpsock_1.c and xdpsock_2.c, and then link the executable
> > +# xdpsock, based on xdpsock_1.o and xdpsock_2.o
> > +#
> > +# Inherited from scripts/Makefile.host
>
> "Inspired by" or "Derived from" would be probably more appropriate term :)
I will replace with "Derived from", looks better.

> > +#
> > +__tprogs := $(sort $(tprogs-y))
> > +
> > +# C code
> > +# Executables compiled from a single .c file
> > +tprog-csingle  := $(foreach m,$(__tprogs), \
> > +                       $(if $($(m)-objs),,$(m)))
> > +
> > +# C executables linked based on several .o files
> > +tprog-cmulti   := $(foreach m,$(__tprogs),\
> > +                       $(if $($(m)-objs),$(m)))
> > +
> > +# Object (.o) files compiled from .c files
> > +tprog-cobjs    := $(sort $(foreach m,$(__tprogs),$($(m)-objs)))
> > +
> > +tprog-csingle  := $(addprefix $(obj)/,$(tprog-csingle))
> > +tprog-cmulti   := $(addprefix $(obj)/,$(tprog-cmulti))
> > +tprog-cobjs    := $(addprefix $(obj)/,$(tprog-cobjs))
> > +
> > +#####
> > +# Handle options to gcc. Support building with separate output directory
> > +
> > +_tprogc_flags   = $(TPROGS_CFLAGS) \
> > +                 $(TPROGCFLAGS_$(basetarget).o)
> > +
> > +# $(objtree)/$(obj) for including generated headers from checkin source files
> > +ifeq ($(KBUILD_EXTMOD),)
> > +ifdef building_out_of_srctree
> > +_tprogc_flags   += -I $(objtree)/$(obj)
> > +endif
> > +endif
> > +
> > +tprogc_flags    = -Wp,-MD,$(depfile) $(_tprogc_flags)
> > +
> > +# Create executable from a single .c file
> > +# tprog-csingle -> Executable
> > +quiet_cmd_tprog-csingle        = CC  $@
> > +      cmd_tprog-csingle        = $(CC) $(tprogc_flags) $(TPROGS_LDFLAGS) -o $@ $< \
> > +               $(TPROGS_LDLIBS) $(TPROGLDLIBS_$(@F))
> > +$(tprog-csingle): $(obj)/%: $(src)/%.c FORCE
> > +       $(call if_changed_dep,tprog-csingle)
> > +
> > +# Link an executable based on list of .o files, all plain c
> > +# tprog-cmulti -> executable
> > +quiet_cmd_tprog-cmulti = LD  $@
> > +      cmd_tprog-cmulti = $(CC) $(tprogc_flags) $(TPROGS_LDFLAGS) -o $@ \
> > +                         $(addprefix $(obj)/,$($(@F)-objs)) \
> > +                         $(TPROGS_LDLIBS) $(TPROGLDLIBS_$(@F))
> > +$(tprog-cmulti): $(tprog-cobjs) FORCE
> > +       $(call if_changed,tprog-cmulti)
> > +$(call multi_depend, $(tprog-cmulti), , -objs)
> > +
> > +# Create .o file from a single .c file
> > +# tprog-cobjs -> .o
> > +quiet_cmd_tprog-cobjs  = CC  $@
> > +      cmd_tprog-cobjs  = $(CC) $(tprogc_flags) -c -o $@ $<
> > +$(tprog-cobjs): $(obj)/%.o: $(src)/%.c FORCE
> > +       $(call if_changed_dep,tprog-cobjs)
> > --
> > 2.17.1
>
> tprogs is quite confusing, but overall looks good to me.
I tend to leave it as tprogs, unless it's going to be progs and agreed with
Yonghong.

It follows logic:
- tprogs for bins
- bpfprogs or bojs or bprogs (could be) for bpf obj

--
Regards,
Ivan Khoronzhuk