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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Yonghong Song <yhs@fb.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <jakub.kicinski@netronome.com>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	john fastabend <john.fastabend@gmail.com>,
	open list <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	clang-built-linux@googlegroups.com,
	sergei.shtylyov@cogentembedded.com
Subject: Re: [PATCH v3 bpf-next 09/14] samples: bpf: makefile: use own flags but not host when cross compile
Date: Wed, 18 Sep 2019 14:29:53 -0700
Message-ID: <CAEf4BzYCNrkaMf-LFHYDi78m9jgMDOswh8VYXGcbttJV-3D21w@mail.gmail.com> (raw)
In-Reply-To: <20190918103508.GC2908@khorivan>

On Wed, Sep 18, 2019 at 3:35 AM Ivan Khoronzhuk
<ivan.khoronzhuk@linaro.org> wrote:
>
> On Tue, Sep 17, 2019 at 04:42:07PM -0700, Andrii Nakryiko wrote:
> >On Mon, Sep 16, 2019 at 3:59 AM Ivan Khoronzhuk
> ><ivan.khoronzhuk@linaro.org> wrote:
> >>
> >> While compile natively, the hosts cflags and ldflags are equal to ones
> >> used from HOSTCFLAGS and HOSTLDFLAGS. When cross compiling it should
> >> have own, used for target arch. While verification, for arm, arm64 and
> >> x86_64 the following flags were used alsways:
> >>
> >> -Wall
> >> -O2
> >> -fomit-frame-pointer
> >> -Wmissing-prototypes
> >> -Wstrict-prototypes
> >>
> >> So, add them as they were verified and used before adding
> >> Makefile.target, but anyway limit it only for cross compile options as
> >> for host can be some configurations when another options can be used,
> >> So, for host arch samples left all as is, it allows to avoid potential
> >> option mistmatches for existent environments.
> >>
> >> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
> >> ---
> >>  samples/bpf/Makefile | 9 +++++++++
> >>  1 file changed, 9 insertions(+)
> >>
> >> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> >> index 1579cc16a1c2..b5c87a8b8b51 100644
> >> --- a/samples/bpf/Makefile
> >> +++ b/samples/bpf/Makefile
> >> @@ -178,8 +178,17 @@ CLANG_EXTRA_CFLAGS := $(ARM_ARCH_SELECTOR)
> >>  TPROGS_CFLAGS += $(ARM_ARCH_SELECTOR)
> >>  endif
> >>
> >> +ifdef CROSS_COMPILE
> >> +TPROGS_CFLAGS += -Wall
> >> +TPROGS_CFLAGS += -O2
> >
> >Specifying one arg per line seems like overkill, put them in one line?
> Will combine.
>
> >
> >> +TPROGS_CFLAGS += -fomit-frame-pointer
> >
> >Why this one?
> I've explained in commit msg. The logic is to have as much as close options
> to have smiliar binaries. As those options are used before for hosts and kinda
> cross builds - better follow same way.

I'm just asking why omit frame pointers and make it harder to do stuff
like profiling? What performance benefits are we seeking for in BPF
samples?

>
> >
> >> +TPROGS_CFLAGS += -Wmissing-prototypes
> >> +TPROGS_CFLAGS += -Wstrict-prototypes
> >
> >Are these in some way special that we want them in cross-compile mode only?
> >
> >All of those flags seem useful regardless of cross-compilation or not,
> >shouldn't they be common? I'm a bit lost about the intent here...
> They are common but split is needed to expose it at least. Also host for
> different arches can have some own opts already used that shouldn't be present
> for cross, better not mix it for safety.

We want -Wmissing-prototypes and -Wstrict-prototypes for cross-compile
and non-cross-compile cases, right? So let's specify them as common
set of options, instead of relying on KBUILD_HOSTCFLAGS or
HOST_EXTRACFLAGS to have them. Otherwise we'll be getting extra
warnings for just cross-compile case, which is not good. If you are
worrying about having duplicate -W flags, seems like it's handled by
GCC already, so shouldn't be a problem.

>
> >
> >> +else
> >>  TPROGS_LDLIBS := $(KBUILD_HOSTLDLIBS)
> >>  TPROGS_CFLAGS += $(KBUILD_HOSTCFLAGS) $(HOST_EXTRACFLAGS)
> >> +endif
> >> +
> >>  TPROGS_CFLAGS += -I$(objtree)/usr/include
> >>  TPROGS_CFLAGS += -I$(srctree)/tools/lib/bpf/
> >>  TPROGS_CFLAGS += -I$(srctree)/tools/testing/selftests/bpf/
> >> --
> >> 2.17.1
> >>
>
> --
> Regards,
> Ivan Khoronzhuk

  reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-16 10:54 [PATCH v3 bpf-next 00/14] samples: bpf: improve/fix cross-compilation Ivan Khoronzhuk
2019-09-16 10:54 ` [PATCH v3 bpf-next 01/14] samples: bpf: makefile: fix HDR_PROBE "echo" Ivan Khoronzhuk
2019-09-16 20:13   ` Andrii Nakryiko
2019-09-16 21:22     ` Ivan Khoronzhuk
2019-09-16 21:35     ` Andreas Schwab
2019-09-16 22:01       ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 02/14] samples: bpf: makefile: fix cookie_uid_helper_example obj build Ivan Khoronzhuk
2019-09-16 20:18   ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 03/14] samples: bpf: makefile: use --target from cross-compile Ivan Khoronzhuk
2019-09-16 20:25   ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 04/14] samples: bpf: use own EXTRA_CFLAGS for clang commands Ivan Khoronzhuk
2019-09-16 20:35   ` Andrii Nakryiko
2019-09-16 22:01     ` Ivan Khoronzhuk
2019-09-16 10:54 ` [PATCH v3 bpf-next 05/14] samples: bpf: makefile: use __LINUX_ARM_ARCH__ selector for arm Ivan Khoronzhuk
2019-09-16 20:44   ` Andrii Nakryiko
2019-09-16 22:04     ` Ivan Khoronzhuk
2019-09-16 10:54 ` [PATCH v3 bpf-next 06/14] samples: bpf: makefile: drop unnecessarily inclusion for bpf_load Ivan Khoronzhuk
2019-09-16 20:52   ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 07/14] samples: bpf: add makefile.target for separate CC target build Ivan Khoronzhuk
2019-09-17 23:19   ` Andrii Nakryiko
2019-09-18 10:12     ` Ivan Khoronzhuk
2019-09-18 21:22       ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 08/14] samples: bpf: makefile: base target programs rules on Makefile.target Ivan Khoronzhuk
2019-09-17 23:28   ` Andrii Nakryiko
2019-09-18 10:23     ` Ivan Khoronzhuk
2019-09-16 10:54 ` [PATCH v3 bpf-next 09/14] samples: bpf: makefile: use own flags but not host when cross compile Ivan Khoronzhuk
2019-09-17 10:14   ` Sergei Shtylyov
2019-09-17 23:42   ` Andrii Nakryiko
2019-09-18 10:35     ` Ivan Khoronzhuk
2019-09-18 21:29       ` Andrii Nakryiko [this message]
2019-09-19 14:18         ` Ivan Khoronzhuk
2019-09-19 17:54           ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 10/14] samples: bpf: makefile: use target CC environment for HDR_PROBE Ivan Khoronzhuk
2019-09-18  4:20   ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 11/14] libbpf: makefile: add C/CXX/LDFLAGS to libbpf.so and test_libpf targets Ivan Khoronzhuk
2019-09-18  5:19   ` Andrii Nakryiko
2019-09-18 11:05     ` Ivan Khoronzhuk
2019-09-18 21:42       ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 12/14] samples: bpf: makefile: provide C/CXX/LD flags to libbpf Ivan Khoronzhuk
2019-09-18  5:20   ` Andrii Nakryiko
2019-09-16 10:54 ` [PATCH v3 bpf-next 13/14] samples: bpf: makefile: add sysroot support Ivan Khoronzhuk
2019-09-18  5:23   ` Andrii Nakryiko
2019-09-18 11:09     ` Ivan Khoronzhuk
2019-09-16 10:54 ` [PATCH v3 bpf-next 14/14] samples: bpf: README: add preparation steps and sysroot info Ivan Khoronzhuk
2019-09-18  5:33 ` [PATCH v3 bpf-next 00/14] samples: bpf: improve/fix cross-compilation Andrii Nakryiko

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