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

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Date:   Sat, 14 Sep 2019 01:14:54 +0300
From:   Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
To:     Yonghong Song <yhs@...com>
Cc:     "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        "hawk@...nel.org" <hawk@...nel.org>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH bpf-next 07/11] samples: bpf: add makefile.prog for
 separate CC build

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@...aro.org>
>> ---
>>   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