From: "H.J. Lu" <hjl.tools@gmail.com>
To: Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH v3 2/5] Make libc symbols hidden in static PIE
Date: Sat, 16 Jan 2021 05:18:21 -0800 [thread overview]
Message-ID: <CAMe9rOqLmxweGz1dFu7+=HkM4yQZOB=eXGPvr6==i5boJaEjqQ@mail.gmail.com> (raw)
In-Reply-To: <CAMe9rOpQZYP+iU7=Gin3eF+9aVV-oUXng3HOsmUtrbD+wM2=7g@mail.gmail.com>
On Fri, Jan 15, 2021 at 4:41 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Fri, Jan 15, 2021 at 2:42 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Fri, Jan 15, 2021 at 7:28 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> > >
> > > On Fri, Jan 15, 2021 at 6:27 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> > > >
> > > > The 01/15/2021 05:43, H.J. Lu wrote:
> > > > > On Fri, Jan 15, 2021 at 3:25 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> > > > > > options:
> > > > > >
> > > > > > (1) fix extern hidden pie calls on i686 (by making
> > > > > > them the same as default vis pie calls so ifuncs
> > > > > > work).
> > > > > >
> > > > > > (2) annotate ifuncs (avoid hidden for them, ifuncs
> > > > > > cannot appear in early start code anyway because
> > > > > > of IRELATIVE): this can be difficult to maintain.
> > > > > >
> > > > > > (3) annotate early object accesses to be hidden so
> > > > > > RELATIVE relocs are avoided. (most targets want
> > > > > > all objects to be hidden, but this solves bug
> > > > > > 27072 without causing problems on i686)
> > > > > >
> > > > > > (4) make pie always use copy relocations on i686.
> > > > > > (and then no hidden annotation is needed, object
> > > > > > access is always local in pie).
> > > > ...
> > > > > > > --- a/elf/dl-reloc-static-pie.c
> > > > > > > +++ b/elf/dl-reloc-static-pie.c
> > > > > > > @@ -17,6 +17,7 @@
> > > > > > > <https://www.gnu.org/licenses/>. */
> > > > > > >
> > > > > > > #if ENABLE_STATIC_PIE
> > > > > > > +#pragma GCC visibility push(hidden)
> > > > > >
> > > > > > yes, this is option (3). you will also need it in _dl_aux_init
> > > > > > and __libc_init_secure and __tunables_init.
> > > > >
> > > > > I will try it.
> > > >
> > > > the naive way does not seem to work:
> > > >
> > > > _dl_support.c has _dl_aux_init as well as _dl_non_dynamic_init,
> > > > the former needs hidden the latter does not and calls rawmemchr
> > > > which is ifunc on i686.
> > > >
> > > > i think the easiest fix is to move those two functions into
> > > > separate files. (ideally we would have a small set of files
> > > > that are involved in the start code before self relocation)
> > > >
> > > > now i realized that there is another option:
> > > >
> > > > (5) remove all ifuncs from i686 libc.
> > > >
> > > > i assume there are not many users who care about i686 performance.
> > >
> > > I don't know if this will work on i686. Since i386 doesn't have IP relative
> > > addressing, we can't remove all RELATIVE relocations. We need to
> > > call _dl_aux_init again after relocating PIE. I don't know what other symbols
> > > are affected. My current patches are on users/hjl/pr27072/master branch:
> > >
> > > https://gitlab.com/x86-glibc/glibc/-/commits/users/hjl/pr27072/master
> > >
> >
> > The problem is
> >
> > #ifdef NEED_DL_SYSINFO
> > /* Needed for improved syscall handling on at least x86/Linux. */
> > uintptr_t _dl_sysinfo = DL_SYSINFO_DEFAULT;
> > #endif
> >
> > We can initialize it in _dl_aux_init instead.
> >
> > I am testing this set of patches on top of yours on i686 and x86-64.
> >
>
> They worked and they passed build-many-glibcs.py.
>
I combined my patches, including 4 testcases, with yours in the right
order here:
https://gitlab.com/x86-glibc/glibc/-/commits/users/hjl/pr27072/master
--
H.J.
next prev parent reply other threads:[~2021-01-16 13:18 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-12 17:21 [PATCH v3 0/5] fix ifunc with static pie [BZ #27072] Szabolcs Nagy
2021-01-12 17:21 ` [PATCH v3 1/5] configure: Require PI_STATIC_AND_HIDDEN for static pie Szabolcs Nagy
2021-01-12 18:38 ` Adhemerval Zanella
2021-01-12 17:22 ` [PATCH v3 2/5] Make libc symbols hidden in static PIE Szabolcs Nagy
2021-01-12 23:09 ` H.J. Lu
2021-01-13 0:02 ` H.J. Lu
2021-01-13 0:33 ` H.J. Lu
2021-01-13 1:19 ` H.J. Lu
2021-01-13 9:50 ` Szabolcs Nagy
2021-01-14 11:17 ` Szabolcs Nagy
2021-01-14 15:39 ` H.J. Lu
2021-01-15 3:36 ` H.J. Lu
2021-01-15 4:29 ` H.J. Lu
2021-01-15 11:25 ` Szabolcs Nagy
2021-01-15 13:43 ` H.J. Lu
2021-01-15 14:27 ` Szabolcs Nagy
2021-01-15 15:28 ` H.J. Lu
2021-01-15 22:42 ` H.J. Lu
2021-01-16 0:41 ` H.J. Lu
2021-01-16 13:18 ` H.J. Lu [this message]
2021-01-18 16:22 ` Szabolcs Nagy
2021-01-12 17:22 ` [PATCH v3 3/5] elf: Make the tunable struct definition internal only Szabolcs Nagy
2021-01-13 17:38 ` Adhemerval Zanella
2021-01-12 17:22 ` [PATCH v3 4/5] elf: Avoid RELATIVE relocs in __tunables_init Szabolcs Nagy
2021-01-13 17:42 ` Adhemerval Zanella
2021-01-12 17:23 ` [PATCH v3 5/5] csu: Move static pie self relocation later [BZ #27072] Szabolcs Nagy
2021-01-12 22:55 ` H.J. Lu
2021-01-14 15:49 ` H.J. Lu
2021-01-14 15:52 ` H.J. Lu
2021-01-14 16:01 ` H.J. Lu
2021-01-14 16:26 ` H.J. Lu
2021-01-14 17:19 ` Szabolcs Nagy
2021-01-14 17:59 ` Szabolcs Nagy
2021-01-14 17:05 ` Szabolcs Nagy
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