linux-kernel - Re: [PATCH v3 bpf-next 09/14] samples: bpf: makefile: use own flags but not host when cross compile

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Date:   Tue, 17 Sep 2019 16:42:07 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        john fastabend <john.fastabend@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        clang-built-linux@...glegroups.com,
        sergei.shtylyov@...entembedded.com
Subject: Re: [PATCH v3 bpf-next 09/14] samples: bpf: makefile: use own flags
 but not host when cross compile

On Mon, Sep 16, 2019 at 3:59 AM Ivan Khoronzhuk
<ivan.khoronzhuk@...aro.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@...aro.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?

> +TPROGS_CFLAGS += -fomit-frame-pointer

Why this one?

> +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...

> +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
>