Re: [PATCH v4 08/10] csu: Move static pie self relocation later [BZ #27072]

["H.J. Lu" <hjl.tools@gmail.com>]

On Tue, Jan 19, 2021 at 9:26 AM Fāng-ruì Sòng <maskray@google.com> wrote:
>
> On Tue, Jan 19, 2021 at 9:11 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Tue, Jan 19, 2021 at 9:03 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> > >
> > > The 01/19/2021 08:47, H.J. Lu wrote:
> > > > On Tue, Jan 19, 2021 at 7:32 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > > > On Tue, Jan 19, 2021 at 7:24 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> > > > > > The 01/19/2021 06:48, H.J. Lu wrote:
> > > > > > > On Tue, Jan 19, 2021 at 6:37 AM Adhemerval Zanella via Libc-alpha
> > > > > > > <libc-alpha@sourceware.org> wrote:
> > > > > > > > On 19/01/2021 11:35, Szabolcs Nagy wrote:
> > > > > > > > > the problem is that _dl_phdr is used in ARCH_SETUP_TLS
> > > > > > > > > (to get the tls program headers) so the __ehdr_start
> > > > > > > > > magic should be before that (this only matters if auxv
> > > > > > > > > lacks AT_PHDR for some reason, which should not happen
> > > > > > > > > normally on linux, so testing won't show the problem)
> > > > > > > >
> > > > > > > > By normally do you mean it might happen on a specific kernel version
> > > > > > > > or is it architecture specific?
> > > > > >
> > > > > > i guess __ehdr_start symbol can be useful and with it
> > > > > > glibc does not have to depend on auxv (which an elf
> > > > > > loader like valgrind/qemu-user may get wrong)
> > > > > >
> > > > > > however it is only used as a fallback and on linux
> > > > > > AT_PHDR is always expected to be present. (i don't
> > > > > > know if this ever triggers)
> > > > >
> > > > > Only used on Hurd?
> > > >
> > > > Does arm64 linker always define __ehdr_start?  If yes, can you drop
> > > > "weak," to see if RELATIVE goes away?
> > >
> > > __ehdr_start support was added in binutils 2.23
> >
> > We may assume binutils >= 2.33 when building for static PIE
> > since all static PIE linkers should define __ehdr_start.
> >
> > Does lld define __ehdr_start?
>
> LLD defines __ehdr_start as hidden if it is not a defined symbol in
> -no-pie/-pie/-shared modes.
> The behavior seems to match gold. GNU ld seems to use STB_LOCAL
> STV_DEFAULT but the exterior behavior should be the same.

I am not sure where you got such incorrect info.  Both ld and gold were changed
to STV_HIDDEN in 2013 by the same commit:

ommit cde7cb0129a884a060b99c7c83e8f5c9af728b0a
Author: Maciej W. Rozycki <macro@linux-mips.org>
Date:   Fri May 3 15:19:27 2013 +0000

            gold/
            PR ld/15365
            * layout.cc (Layout::finalize): Make __ehdr_start STV_HIDDEN.

            ld/
            PR ld/15365
            * emultempl/elf32.em (gld${EMULATION_NAME}_before_allocation):
            Restrict __ehdr_start's export class to no less than STV_HIDDEN.

-- 
H.J.