linux-kernel - Re: [PATCH] bpfilter: allow to build bpfilter

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Message-ID: <20200701174609.mw5ovqe7d5o6ptel@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 1 Jul 2020 10:46:09 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kbuild@...r.kernel.org,
        Michal Kubecek <mkubecek@...e.cz>,
        linux-kernel@...r.kernel.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>,
        Sam Ravnborg <sam@...nborg.org>,
        Song Liu <songliubraving@...com>,
        Valdis Kl ē tnieks <valdis.kletnieks@...edu>,
        Yonghong Song <yhs@...com>
Subject: Re: [PATCH] bpfilter: allow to build bpfilter_umh as a module
 without static library

On Wed, Jul 01, 2020 at 06:26:44PM +0900, Masahiro Yamada wrote:
> Originally, bpfilter_umh was linked with -static only when
> CONFIG_BPFILTER_UMH=y.
> 
> Commit 8a2cc0505cc4 ("bpfilter: use 'userprogs' syntax to build
> bpfilter_umh") silently, accidentally dropped the CONFIG_BPFILTER_UMH=y
> test in the Makefile. Revive it in order to link it dynamically when
> CONFIG_BPFILTER_UMH=m.
> 
> Since commit b1183b6dca3e ("bpfilter: check if $(CC) can link static
> libc in Kconfig"), the compiler must be capable of static linking to
> enable CONFIG_BPFILTER_UMH, but it requires more than needed.
> 
> To loosen the compiler requirement, I changed the dependency as follows:
> 
>     depends on CC_CAN_LINK
>     depends on m || CC_CAN_LINK_STATIC
> 
> If CONFIG_CC_CAN_LINK_STATIC in unset, CONFIG_BPFILTER_UMH is restricted
> to 'm' or 'n'.
> 
> In theory, CONFIG_CC_CAN_LINK is not required for CONFIG_BPFILTER_UMH=y,
> but I did not come up with a good way to describe it.
> 
> Fixes: 8a2cc0505cc4 ("bpfilter: use 'userprogs' syntax to build bpfilter_umh")
> Reported-by: Michal Kubecek <mkubecek@...e.cz>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

lgtm
Do you mind I'll take it into bpf-next tree?
Eric is working on a bunch of patches in this area. I'll take his set
into bpf-next as well and then can apply this patch.
Just to make sure there are no conflicts.