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: Thu, 14 Jan 2021 20:29:34 -0800 [thread overview]
Message-ID: <CAMe9rOpmcigsBB8OPHOTJi1qn6xthi_Aj4m4gXHcF_YuRp79nA@mail.gmail.com> (raw)
In-Reply-To: <CAMe9rOptUa1wN=ijCb5KjoTWUh5+GUnZQTZTGkWvRXnA3jeTzg@mail.gmail.com>
On Thu, Jan 14, 2021 at 7:36 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Thu, Jan 14, 2021 at 3:18 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> >
> > The 01/13/2021 09:50, Szabolcs Nagy via Libc-alpha wrote:
> > > The 01/12/2021 17:19, H.J. Lu wrote:
> > > > On Tue, Jan 12, 2021 at 4:33 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > > > On Tue, Jan 12, 2021 at 4:02 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > > > > See:
> > > > > >
> > > > > > https://sourceware.org/bugzilla/show_bug.cgi?id=14961
> > > > > >
> > > > > /* Mark all symbols hidden in static PIE libc to avoid GOT indirections. */
> > > > > -#if BUILD_PIE_DEFAULT && IS_IN (libc) && !defined LIBC_NONSHARED
> > > > > +#if BUILD_PIE_DEFAULT && !defined NO_HIDDEN_EXTERN_FUNC_IN_PIE \
> > > > > + && IS_IN (libc) && !defined LIBC_NONSHARED
> > > > > # pragma GCC visibility push(hidden)
> > > > > #endif
> > > > >
> > > >
> > > > This works on i686.
> >
> > The series i plan to commit today is in nsz/bug27072 now,
> >
> > This is the v4 of this patch:
> >
> > Hidden matters with static PIE: extern symbol access in position
> > independent code usually involves GOT indirections which needs
> > RELATIVE relocs in a static linked PIE. Hidden visibility avoids
> > indirections and RELATIVE relocs on targets that can access symbols
> > pc-relative.
> >
> > The check should use IS_IN_LIB instead of IS_IN(libc) since all
> > static libraries can use hidden visibility to avoid indirections,
> > however the test system links objects from libcrypt.a into dynamic
> > linked test binaries so hidden does not work there. I think mixing
> > static and shared libc components in the same binary should not be
> > supported usage, but to be safe only use hidden in libc.a.
> >
> > There are targets (i686) where hidden visibility functions are
> > problematic in PIE code so hidden cannot be applied to all symbols.
> > Then static PIE requires extern object access without relocations
> > (e.g. by relying on copy relocations in shared libraries instead of
> > GOT access in PIE code). See bug 14961.
>
> It isn't about copy relocations. It is IFUNC, PLT and PIE. I needed
> additional patches to make static PIE to work on i386 and x86-64.
> I am enclosing my patches. Please include them in your patch set.
>
> > From -static-pie linked 'int main(){}' this shaves off 73 relative
> > relocs on aarch64 and reduces code size too.
>
>
> --
> H.J.
commit c5ffa46591550d945b009f0e3bcf66603d48ac0b
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Thu Jan 14 13:26:29 2021 -0800
i386: Call _dl_aux_init after relocating static PIE
is too complicated. I will submit a simple version.
--
H.J.
next prev parent reply other threads:[~2021-01-15 4:30 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 [this message]
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
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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