Re: [PATCH bpf-next 07/11] samples: bpf: add makefile.prog for separate CC build

[Ivan Khoronzhuk]

On Fri, Sep 13, 2019 at 09:33:58PM +0000, Yonghong Song wrote:
> On 9/10/19 11:38 AM, Ivan Khoronzhuk wrote:
> > The makefile.prog is added only, will be used in sample/bpf/Makefile
> > later in order to switch cross-compiling on CC from HOSTCC.
> >
> > 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.prog 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.
>
> So this is really Makefile.host or Makefile.user, right?
It's cut and modified version of Makefile.host

> In BPF, 'prog' can refers to user prog or bpf prog.
> To avoid ambiguity, maybe Makefile.host?
Makefile.target? as target = host not always.
Makefile.user also looks ok, but doesn't contain target,
maybe "targetuser", but bpf is also target...
Initially I was thinking about Makefile.targetprog, but it looks too long.

> > Makefile.prog contains only stuff needed for samples/bpf, potentially
> > can be reused and extended for other prog sets later and now needed
>
> What do you mean 'extended for other prog sets'? I am wondering whether
Another kind of samples...with c++ for instance.

> we could just include 'scripts/Makefile.host'? How hard it is?
It's bound to HOSTCC and it's environment. It is included by default and
was used before this patchset, blocking cross complication.

> > only for unblocking tricky samples/bpf cross compilation.
> >
> > Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
> > ---
> >   samples/bpf/Makefile.prog | 77 +++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 77 insertions(+)
> >   create mode 100644 samples/bpf/Makefile.prog
> >
> > diff --git a/samples/bpf/Makefile.prog b/samples/bpf/Makefile.prog
> > new file mode 100644
> > index 000000000000..3781999b9193
> > --- /dev/null
> > +++ b/samples/bpf/Makefile.prog
> > @@ -0,0 +1,77 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +# ==========================================================================
> > +# Building binaries on the host system
> > +# Binaries are not used during the compilation of the kernel, and intendent
> > +# to be build for target board, target board can be host ofc. Added to build
> > +# binaries to run not on host system.
> > +#
> > +# Only C is supported, but can be extended for C++.
>
> The above comment is not needed.
will drop it.

> samples/bpf/ only have C now. I am wondering whether your below scripts
> can be simplified, e.g., removing cxxobjs.
I think yes, will try

> > +#
> > +# Sample syntax (see Documentation/kbuild/makefiles.rst for reference)
> > +# progs-y := xsk_example
> > +# Will compile xdpsock_example.c and create an executable named xsk_example
> > +#
> > +# progs-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
> > +#
> > +__progs := $(sort $(progs-y))
> > +
> > +# C code
> > +# Executables compiled from a single .c file
> > +prog-csingle	:= $(foreach m,$(__progs), \
> > +			$(if $($(m)-objs)$($(m)-cxxobjs),,$(m)))
> > +
> > +# C executables linked based on several .o files
> > +prog-cmulti	:= $(foreach m,$(__progs),\
> > +		   $(if $($(m)-cxxobjs),,$(if $($(m)-objs),$(m))))
> > +
> > +# Object (.o) files compiled from .c files
> > +prog-cobjs	:= $(sort $(foreach m,$(__progs),$($(m)-objs)))
> > +
> > +prog-csingle	:= $(addprefix $(obj)/,$(prog-csingle))
> > +prog-cmulti	:= $(addprefix $(obj)/,$(prog-cmulti))
> > +prog-cobjs	:= $(addprefix $(obj)/,$(prog-cobjs))
> > +
> > +#####
> > +# Handle options to gcc. Support building with separate output directory
> > +
> > +_progc_flags   = $(PROGS_CFLAGS) \
> > +                 $(PROGCFLAGS_$(basetarget).o)
> > +
> > +# $(objtree)/$(obj) for including generated headers from checkin source files
> > +ifeq ($(KBUILD_EXTMOD),)
> > +ifdef building_out_of_srctree
> > +_progc_flags   += -I $(objtree)/$(obj)
> > +endif
> > +endif
> > +
> > +progc_flags    = -Wp,-MD,$(depfile) $(_progc_flags)
> > +
> > +# Create executable from a single .c file
> > +# prog-csingle -> Executable
> > +quiet_cmd_prog-csingle 	= CC  $@
> > +      cmd_prog-csingle	= $(CC) $(progc_flags) $(PROGS_LDFLAGS) -o $@ $< \
> > +		$(PROGS_LDLIBS) $(PROGLDLIBS_$(@F))
> > +$(prog-csingle): $(obj)/%: $(src)/%.c FORCE
> > +	$(call if_changed_dep,prog-csingle)
> > +
> > +# Link an executable based on list of .o files, all plain c
> > +# prog-cmulti -> executable
> > +quiet_cmd_prog-cmulti	= LD  $@
> > +      cmd_prog-cmulti	= $(CC) $(progc_flags) $(PROGS_LDFLAGS) -o $@ \
> > +			  $(addprefix $(obj)/,$($(@F)-objs)) \
> > +			  $(PROGS_LDLIBS) $(PROGLDLIBS_$(@F))
> > +$(prog-cmulti): $(prog-cobjs) FORCE
> > +	$(call if_changed,prog-cmulti)
> > +$(call multi_depend, $(prog-cmulti), , -objs)
> > +
> > +# Create .o file from a single .c file
> > +# prog-cobjs -> .o
> > +quiet_cmd_prog-cobjs	= CC  $@
> > +      cmd_prog-cobjs	= $(CC) $(progc_flags) -c -o $@ $<
> > +$(prog-cobjs): $(obj)/%.o: $(src)/%.c FORCE
> > +	$(call if_changed_dep,prog-cobjs)

--
Regards,
Ivan Khoronzhuk