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

Fangrui Song
2022-11-15T00:46:38Z

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@google.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@google.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.