netdev - Re: [PATCH 3/3] bpfilter: do not (ab)use host-program build rule

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Date:   Sun, 10 Jun 2018 00:13:43 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        YueHaibing <yuehaibing@...wei.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH 3/3] bpfilter: do not (ab)use host-program build rule

2018-06-09 5:52 GMT+09:00 Alexei Starovoitov <alexei.starovoitov@...il.com>:
> On Sat, Jun 09, 2018 at 02:12:10AM +0900, Masahiro Yamada wrote:
>> It is an ugly hack to overwrite $(HOSTCC) with $(CC) to reuse the
>> build rules from scripts/Makefile.host.  It should not be tedious
>> to write a build rule for its own.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> ---
>>
>>  net/bpfilter/Makefile                   | 17 +++++++++++------
>>  net/bpfilter/{main.c => bpfilter_umh.c} |  0
>>  2 files changed, 11 insertions(+), 6 deletions(-)
>>  rename net/bpfilter/{main.c => bpfilter_umh.c} (100%)
>>
>> diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile
>> index 39c6980..6571b30 100644
>> --- a/net/bpfilter/Makefile
>> +++ b/net/bpfilter/Makefile
>> @@ -3,18 +3,23 @@
>>  # Makefile for the Linux BPFILTER layer.
>>  #
>>
>> -hostprogs-y := bpfilter_umh
>> -bpfilter_umh-objs := main.o
>> -HOSTCFLAGS += -I. -Itools/include/ -Itools/include/uapi
>> -HOSTCC := $(CC)
>
> that is a hack indeed. I don't like it either, but see below.
>
>> -
>>  ifeq ($(CONFIG_BPFILTER_UMH), y)
>>  # builtin bpfilter_umh should be compiled with -static
>>  # since rootfs isn't mounted at the time of __init
>>  # function is called and do_execv won't find elf interpreter
>> -HOSTLDFLAGS += -static
>> +STATIC := -static
>>  endif
>>
>> +quiet_cmd_cc_user = CC      $@
>> +      cmd_cc_user = $(CC) -Wall -Wmissing-prototypes -O2 -std=gnu89 \
>> +                 -I$(srctree) -I$(srctree)/tools/include/ \
>> +                 -I$(srctree)/tools/include/uapi $(STATIC) -o $@ $<
>> +
>> +$(obj)/bpfilter_umh: $(src)/bpfilter_umh.c FORCE
>> +     $(call if_changed,cc_user)
>
> Does this scale?
> Please see two top patches here:
> https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/log/?h=ipt_bpf
> that add more meat to bpfilter and a lot more files.

Oh, I just thought main.c was the only user-program file.

> Recompiling all of them at once isn't nice either.

Indeed.

It should be able to compile .c -> .o separately.

> This Makefile needs different .c -> .o rules for bpfilter_kern.c files
> that get compiled into kernel module and for the rest of umh files:
> main.c ctor.c init.c gen.c etc
> that need to be compiled .c -> .o differently.
> I don't see how to do it without ugly hacks in Makefile.
> In that sense HOSTCC = CC hack looked the least ugly to me that's
> why I went with it.
> Better ideas?


I will think about it after your patches land.

I will drop this for now.


-- 
Best Regards
Masahiro Yamada