Received-SPF: pass (google.com: domain of linux-kernel+bounces-152258-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240415162041.2491523-5-ardb+git@google.com> <171327842741.29461.3030265084386428643.git-patchwork-notify@kernel.org>
 <CAMj1kXGVRGcJGS1xuqHPeJfM797RB2UiJQfSHK+oj1JQG4YECg@mail.gmail.com>
In-Reply-To: <CAMj1kXGVRGcJGS1xuqHPeJfM797RB2UiJQfSHK+oj1JQG4YECg@mail.gmail.com>
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Sat, 20 Apr 2024 21:31:44 +0900
Message-ID: <CAK7LNAQ8fhKUwK_m8uGfvBUBrAdXdMYM3_AA5zo2cQzhW3jE1A@mail.gmail.com>
Subject: Re: [PATCH v4 0/3] kbuild: Avoid weak external linkage where possible
To: Ard Biesheuvel <ardb@kernel.org>
Cc: patchwork-bot+netdevbpf@kernel.org, Ard Biesheuvel <ardb+git@google.com>, 
	linux-kernel@vger.kernel.org, arnd@arndb.de, martin.lau@linux.dev, 
	linux-arch@vger.kernel.org, linux-kbuild@vger.kernel.org, bpf@vger.kernel.org, 
	andrii@kernel.org, olsajiri@gmail.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Fri, Apr 19, 2024 at 4:57=E2=80=AFPM Ard Biesheuvel <ardb@kernel.org> wr=
ote:
>
> On Tue, 16 Apr 2024 at 16:40, <patchwork-bot+netdevbpf@kernel.org> wrote:
> >
> > Hello:
> >
> > This series was applied to bpf/bpf-next.git (master)
> > by Daniel Borkmann <daniel@iogearbox.net>:
> >
> > On Mon, 15 Apr 2024 18:20:42 +0200 you wrote:
> > > From: Ard Biesheuvel <ardb@kernel.org>
> > >
> > > Weak external linkage is intended for cases where a symbol reference
> > > can remain unsatisfied in the final link. Taking the address of such =
a
> > > symbol should yield NULL if the reference was not satisfied.
> > >
> > > Given that ordinary RIP or PC relative references cannot produce NULL=
,
> > > some kind of indirection is always needed in such cases, and in posit=
ion
> > > independent code, this results in a GOT entry. In ordinary code, it i=
s
> > > arch specific but amounts to the same thing.
> > >
> > > [...]
> >
> > Here is the summary with links:
> >   - [v4,1/3] kallsyms: Avoid weak references for kallsyms symbols
> >     (no matching commit)
> >   - [v4,2/3] vmlinux: Avoid weak reference to notes section
> >     (no matching commit)
> >   - [v4,3/3] btf: Avoid weak external references
> >     https://git.kernel.org/bpf/bpf-next/c/fc5eb4a84e4c
> >
>
>
> Thanks.
>
> Masahiro, could you pick up patches #1 and #2 please?
>


I do not like PROVIDE() because it potentially shifts
a build error (i.e. link error) into
a run-time error, which is usually more difficult to debug
than build error.

If someone references the kallsyms_* symbols
when CONFIG_KALLSYMS=3Dn, it is likely a mistake.
In general, it should be reported as a link error.

With PROVIDE() added, we will never detect it
at a build time.

Do you want me to pick up 1/3?


--
Best Regards
Masahiro Yamada