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

[Fangrui Song]

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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > > ---
> > > > [...]
> > >
> > > 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.