On Tue, Sep 21, 2021 at 6:57 PM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> On Tue, Sep 21, 2021 at 9:16 AM Uros Bizjak <ubiz...@gmail.com> wrote:
> >
> > On Mon, Sep 20, 2021 at 8:20 PM Fāng-ruì Sòng via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > PING^5 https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html
> > >
> > > On Sat, Sep 4, 2021 at 12:11 PM Fāng-ruì Sòng <mask...@google.com> wrote:
> > > >
> > > > PING^4 https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html
> > > >
> > > > One major design goal of PIE was to avoid copy relocations.
> > > > The original patch for GCC 5 caused problems for many years.
> > > >
> > > > On Wed, Aug 18, 2021 at 11:54 PM Fāng-ruì Sòng <mask...@google.com> 
> > > > wrote:
> > > >>
> > > >> PING^3 https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html
> > > >>
> > > >> On Fri, Jun 4, 2021 at 3:04 PM Fāng-ruì Sòng <mask...@google.com> 
> > > >> wrote:
> > > >> >
> > > >> > PING^2 https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html
> > > >> >
> > > >> > On Mon, May 24, 2021 at 9:43 AM Fāng-ruì Sòng <mask...@google.com> 
> > > >> > wrote:
> > > >> > >
> > > >> > > Ping https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570139.html
> > > >> > >
> > > >> > > On Tue, May 11, 2021 at 8:29 PM Fangrui Song <mask...@google.com> 
> > > >> > > wrote:
> > > >> > > >
> > > >> > > > This was introduced in 2014-12 to use local binding for external 
> > > >> > > > symbols
> > > >> > > > for -fPIE. Now that we have H.J. Lu's GOTPCRELX for years which 
> > > >> > > > mostly
> > > >> > > > nullify the benefit of HAVE_LD_PIE_COPYRELOC, 
> > > >> > > > HAVE_LD_PIE_COPYRELOC
> > > >> > > > should retire now.
> > > >> > > >
> > > >> > > > One design goal of -fPIE was to avoid copy relocations.
> > > >> > > > HAVE_LD_PIE_COPYRELOC has deviated from the goal.  With this 
> > > >> > > > change, the
> > > >> > > > -fPIE behavior of x86-64 will be closer to x86-32 and other 
> > > >> > > > targets.
> > > >> > > >
> > > >> > > > ---
> > > >> > > >
> > > >> > > > See https://gcc.gnu.org/legacy-ml/gcc/2019-05/msg00215.html for 
> > > >> > > > a list
> > > >> > > > of fixed and unfixed (e.g. gold incompatibility with protected
> > > >> > > > https://sourceware.org/bugzilla/show_bug.cgi?id=19823) issues.
> > > >> > > >
> > > >> > > > If you prefer a longer write-up, see
> > > >> > > > https://maskray.me/blog/2021-01-09-copy-relocations-canonical-plt-entries-and-protected
> > > >> > > > ---
> > > >> > > >  gcc/config.in                                 |  6 ---
> > > >> > > >  gcc/config/i386/i386.c                        | 11 +---
> > > >> > > >  gcc/configure                                 | 52 
> > > >> > > > -------------------
> > > >> > > >  gcc/configure.ac                              | 48 
> > > >> > > > -----------------
> > > >> > > >  gcc/doc/sourcebuild.texi                      |  3 --
> > > >> > > >  .../gcc.target/i386/pie-copyrelocs-1.c        | 14 -----
> > > >> > > >  .../gcc.target/i386/pie-copyrelocs-2.c        | 14 -----
> > > >> > > >  .../gcc.target/i386/pie-copyrelocs-3.c        | 14 -----
> > > >> > > >  .../gcc.target/i386/pie-copyrelocs-4.c        | 17 ------
> > > >> > > >  gcc/testsuite/lib/target-supports.exp         | 47 
> > > >> > > > -----------------
> > > >> > > >  10 files changed, 2 insertions(+), 224 deletions(-)
> > > >> > > >  delete mode 100644 
> > > >> > > > gcc/testsuite/gcc.target/i386/pie-copyrelocs-1.c
> > > >> > > >  delete mode 100644 
> > > >> > > > gcc/testsuite/gcc.target/i386/pie-copyrelocs-2.c
> > > >> > > >  delete mode 100644 
> > > >> > > > gcc/testsuite/gcc.target/i386/pie-copyrelocs-3.c
> > > >> > > >  delete mode 100644 
> > > >> > > > gcc/testsuite/gcc.target/i386/pie-copyrelocs-4.c
> >
> > From x86 maintainer's PoV, the implementation is trivially correct,
> > but I have no idea about functionality. HJ, can you please review the
> > functionality and post your opinion on the patch to move it forward?
> >
> > Thanks,
> > Uros.
>
> I prefer to leave it alone and apply this:
>
> https://gcc.gnu.org/pipermail/gcc-patches/2021-August/576736.html
>
> instead.  I am working to add a nodirect_extern_access attribute based
> on feedback at LPC 2021.

I think -fpie should be fixed as soon as possible.

"Add -f[no-]direct-extern-access" says "-fdirect-extern-access is the default."
IMHO this is not a good choice for -fpie.
As the description of this patch says, one of the design goals of
-fpie is to avoid copy relocations.

> In executable and shared library, bind symbols with the STV_PROTECTED 
> visibility locally

As I have repeated many times (also Clang's behavior), STV_PROTECTED
visibility symbol should be bound locally regardless of
-fno-direct-extern-access.

I think it is fair to say all of Michael Matz, Alan Modra, and I think
adding so many behaviors under -fno-direct-extern-access is
over-engineering (well, because I don't think
-fno-direct-extern-access can be selected as the default behavior any
time soon).

https://maskray.me/blog/2021-01-09-copy-relocations-canonical-plt-entries-and-protected#summary

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