netdev - Re: [PATCH v4 bpf-next 1/4] selftests/bpf: compile progs with -D__TARGET_ARCH

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Message-Id: <6E5C9DDE-FF1D-4BFA-813E-7A0C3232B5F0@linux.ibm.com>
Date:   Fri, 12 Jul 2019 10:59:55 +0200
From:   Ilya Leoshkevich <iii@...ux.ibm.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Y Song <ys114321@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Stanislav Fomichev <sdf@...ichev.me>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH v4 bpf-next 1/4] selftests/bpf: compile progs with
 -D__TARGET_ARCH_$(SRCARCH)

> Am 12.07.2019 um 02:53 schrieb Andrii Nakryiko <andrii.nakryiko@...il.com>:
> 
> On Thu, Jul 11, 2019 at 7:32 AM Ilya Leoshkevich <iii@...ux.ibm.com> wrote:
>> 
>> This opens up the possibility of accessing registers in an
>> arch-independent way.
>> 
>> Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
>> ---
>> tools/testing/selftests/bpf/Makefile | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>> 
>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>> index 2620406a53ec..ad84450e4ab8 100644
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -1,4 +1,5 @@
>> # SPDX-License-Identifier: GPL-2.0
>> +include ../../../scripts/Makefile.arch
>> 
>> LIBDIR := ../../../lib
>> BPFDIR := $(LIBDIR)/bpf
>> @@ -138,7 +139,8 @@ CLANG_SYS_INCLUDES := $(shell $(CLANG) -v -E - </dev/null 2>&1 \
>> 
>> CLANG_FLAGS = -I. -I./include/uapi -I../../../include/uapi \
>>              $(CLANG_SYS_INCLUDES) \
>> -             -Wno-compare-distinct-pointer-types
>> +             -Wno-compare-distinct-pointer-types \
>> +             -D__TARGET_ARCH_$(SRCARCH)
> 
> samples/bpf/Makefile uses $(ARCH), why does it work for samples?
> Should we update samples/bpf/Makefile as well?

I believe that in common cases both are okay, but judging by
linux:Makefile and linux:tools/scripts/Makefile.arch, one could use e.g.
ARCH=i686, and that would be converted to SRCARCH=x86. So IMHO SRCARCH
is safer, and we should change bpf/samples/Makefile. I could send a
patch separately.