netdev - Re: [PATCH bpf-next 2/8] samples: bpf: Makefile: remove target for native build

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Date:   Fri, 6 Sep 2019 17:04:08 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...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>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH bpf-next 2/8] samples: bpf: Makefile: remove target for
 native build

On Fri, Sep 6, 2019 at 4:52 PM Ivan Khoronzhuk
<ivan.khoronzhuk@...aro.org> wrote:
>
> On Fri, Sep 06, 2019 at 04:31:39PM -0700, Alexei Starovoitov wrote:
> >On Thu, Sep 05, 2019 at 12:22:06AM +0300, Ivan Khoronzhuk wrote:
> >> No need to set --target for native build, at least for arm, the
> >> default target will be used anyway. In case of arm, for at least
> >> clang 5 - 10 it causes error like:
> >>
> >> clang: warning: unknown platform, assuming -mfloat-abi=soft
> >> LLVM ERROR: Unsupported calling convention
> >> make[2]: *** [/home/root/snapshot/samples/bpf/Makefile:299:
> >> /home/root/snapshot/samples/bpf/sockex1_kern.o] Error 1
> >>
> >> Only set to real triple helps: --target=arm-linux-gnueabihf
> >> or just drop the target key to use default one. Decision to just
> >> drop it and thus default target will be used (wich is native),
> >> looks better.
> >>
> >> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
> >> ---
> >>  samples/bpf/Makefile | 2 --
> >>  1 file changed, 2 deletions(-)
> >>
> >> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> >> index 61b7394b811e..a2953357927e 100644
> >> --- a/samples/bpf/Makefile
> >> +++ b/samples/bpf/Makefile
> >> @@ -197,8 +197,6 @@ BTF_PAHOLE ?= pahole
> >>  ifdef CROSS_COMPILE
> >>  HOSTCC = $(CROSS_COMPILE)gcc
> >>  CLANG_ARCH_ARGS = --target=$(notdir $(CROSS_COMPILE:%-=%))
> >> -else
> >> -CLANG_ARCH_ARGS = -target $(ARCH)
> >>  endif
> >
> >I don't follow here.
> >Didn't you introduce this bug in patch 1 and now fixing it in patch 2?
> >
>
> It looks like but that's not true.
> Previous patch adds target only for cross compiling,
> before the patch the target was used for both, cross compiling and w/o cc.
>
> This patch removes target only for native build (it's not cross compiling).
>
> By fact, it's two separate significant changes.

How so?
before first patch CLANG_ARCH_ARGS is only used under CROSS_COMPILE.
After the first patch CLANG_ARCH_ARGS is now suddenly defined w/o CROSS_COMPILE
and second patch brings it to the state before first patch.