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

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Message-ID: <3ec9737e-3d1a-c014-b91a-0e2d406a3b3d@csgroup.eu>
Date:   Sun, 4 Dec 2022 16:58:53 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Fangrui Song <maskray@...gle.com>,
        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



Le 04/12/2022 à 05:50, Fangrui Song a écrit :
> 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

Well, there was a typo in my question, I wanted to ask 'why', not 'which'.

>>
>>     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 :)

Ok, that seems to work on powerpc.

Reviewed-by: Christophe Leroy <christophe.leroy@...roup.eu>