netdev - Re: [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build bpfilter

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Date:   Mon, 8 Jun 2020 13:56:28 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, bpf@...r.kernel.org,
        Sam Ravnborg <sam@...nborg.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build
 bpfilter_umh

On Thu, Apr 23, 2020 at 04:39:17PM +0900, Masahiro Yamada wrote:
> The user mode helper should be compiled for the same architecture as
> the kernel.
> 
> This Makefile reuses the 'hostprogs' syntax by overriding HOSTCC with CC.
> 
> Now that Kbuild provides the syntax 'userprogs', use it to fix the
> Makefile mess.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> Reported-by: kbuild test robot <lkp@...el.com>
> ---
> 
>  net/bpfilter/Makefile | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile
> index 36580301da70..6ee650c6badb 100644
> --- a/net/bpfilter/Makefile
> +++ b/net/bpfilter/Makefile
> @@ -3,17 +3,14 @@
>  # Makefile for the Linux BPFILTER layer.
>  #
>  
> -hostprogs := bpfilter_umh
> +userprogs := bpfilter_umh
>  bpfilter_umh-objs := main.o
> -KBUILD_HOSTCFLAGS += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi
> -HOSTCC := $(CC)
> +user-ccflags += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi
>  
> -ifeq ($(CONFIG_BPFILTER_UMH), y)
> -# builtin bpfilter_umh should be compiled with -static
> +# builtin bpfilter_umh should be linked with -static
>  # since rootfs isn't mounted at the time of __init
>  # function is called and do_execv won't find elf interpreter
> -KBUILD_HOSTLDFLAGS += -static
> -endif
> +bpfilter_umh-ldflags += -static
>  
>  $(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh

Hello,

I just noticed that this patch (now in mainline as commit 8a2cc0505cc4)
drops the test if CONFIG_BPFILTER_UMH is "y" so that -static is now
passed to the linker even if bpfilter_umh is built as a module which
wasn't the case in v5.7.

This is not mentioned in the commit message and the comment still says
"*builtin* bpfilter_umh should be linked with -static" so this change
doesn't seem to be intentional. Did I miss something?

Michal Kubecek