linux-kernel - Re: [PATCH] vdso: Improve cmd_vdso_check to check all dynamic relocations

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Message-ID: <CAFP8O3LdSJCChGEwT57e=iZopceYkBFuW9XD=yhO1ZszVZGm4g@mail.gmail.com>
Date:   Sat, 3 Dec 2022 20:50:40 -0800
From:   Fangrui Song <maskray@...gle.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] vdso: Improve cmd_vdso_check to check all dynamic relocations

On Mon, Nov 14, 2022 at 4:46 PM Fangrui Song <maskray@...gle.com> wrote:
>
> On 2022-11-14, Christophe Leroy wrote:
> >
> >
> >Le 28/09/2022 à 07:25, Fangrui Song a écrit :
> >> On Sat, Sep 10, 2022 at 12:53 AM Fangrui Song <maskray@...gle.com> wrote:
> >>>
> >>> On 2022-08-30, Fangrui Song wrote:
> >>>> The actual intention is that no dynamic relocation exists. However, some
> >>>> GNU ld ports produce unneeded R_*_NONE. (If a port is not care enough to
> >>>> determine the exact .rel[a].dyn size, the trailing zeros become R_*_NONE
> >>>> relocations. E.g. powerpc64le ld as of 2.38 has the issue with
> >>>> defconfig.) R_*_NONE are generally no-op in the dynamic loaders. So just
> >>>> ignore them.
> >>>>
> >>>> With the change, we can remove ARCH_REL_TYPE_ABS. ARCH_REL_TYPE_ABS is a
> >>>> bit misnomer as ports may check RELAVETIVE/GLOB_DAT/JUMP_SLOT which are
> >>>> not called "absolute relocations". (The patch is motivated by the arm64
> >>>> port missing R_AARCH64_RELATIVE.)
> >>>>
> >>>> While here, replace "egrep" with "grep" as "egrep" is deprecated in GNU
> >>>> grep 3.7.
> >>>>
> >>>> Signed-off-by: Fangrui Song <maskray@...gle.com>
> >>>> ---
> >>>> [...]
> >>>>
> >>>
> >>> Ping.
> >>
> >> Ping^2 :)
> >
> >Can you explain which ARCH_REL_TYPE_ABS can be removed with this change ?
> >How is the verification done if ARCH_REL_TYPE_ABS is removed ?
>
> All ARCH_REL_TYPE_ABS relocation types can be removed. As explained, the
> real intention is to check no dynamic relocation, and this is done by
> the new
>
>    cmd_vdso_check = if $(READELF) -rW $@ | grep -v _NONE | grep -q "R_\w*_"; \
>
> in this patch.
>
> grep -v _NONE is to work around some GNU ld ports (and likely older releases
> of some ports even if their latest versions are fixed) which produce
> unneeded R_*_NONE dynamic relocations.

Ping :)