[Bug dynamic-link/28656] New: LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[Bug dynamic-link/28656] New: LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28656

            Bug ID: 28656
           Summary: LD_PREFER_MAP_32BIT_EXEC no longer works due to
                    binutils changes
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
  Target Milestone: ---
              Host: x86-64

The first LOAD segment of system libraries is no longer executable, which
disables MAP_32BIT processing with LD_PREFER_MAP_32BIT_EXEC. This is a result
of a binutils change (likely defaulting to -z separate-code).

I think we should recommend using a PIE executable with an explicit loader
invocation as a replacement.  It achieves the same effect (everything is mapped
into one 4 GB window):

$ /lib64/ld-linux-x86-64.so.2 /bin/cut -d ' ' -f 1 /proc/self/maps 
55555701b000-55555703c000
7f09b3b3c000-7f09b3b91000
7f09b3b91000-7f09b3e09000
7f09b3e09000-7f09b3e0c000
7f09b3e0c000-7f09b3e38000
7f09b3e38000-7f09b3fae000
7f09b3fae000-7f09b4002000
7f09b4002000-7f09b4003000
7f09b4003000-7f09b4006000
7f09b4006000-7f09b4009000
7f09b4009000-7f09b4018000
7f09b4019000-7f09b401a000
7f09b401a000-7f09b401b000
7f09b401b000-7f09b401c000
7f09b401c000-7f09b401d000
7f09b401d000-7f09b401e000
7f09b401e000-7f09b401f000
7f09b401f000-7f09b4020000
7f09b4020000-7f09b4021000
7f09b4021000-7f09b4022000
7f09b4022000-7f09b4029000
7f09b4029000-7f09b402a000
7f09b402a000-7f09b402c000
7f09b402c000-7f09b4032000
7f09b4032000-7f09b4034000
7f09b4034000-7f09b4035000
7f09b4035000-7f09b4036000
7f09b4036000-7f09b4037000
7f09b4037000-7f09b4038000
7f09b4038000-7f09b405e000
7f09b405e000-7f09b4068000
7f09b4068000-7f09b406a000
7f09b406a000-7f09b406c000
7ffd90134000-7ffd90155000
7ffd901fa000-7ffd901fe000
7ffd901fe000-7ffd90200000
ffffffffff600000-ffffffffff601000

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[Bug dynamic-link/28656] LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28656

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
Created attachment 13843
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13843&action=edit
A patch

How about this?

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[Bug dynamic-link/28656] LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28656

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #13843|0                           |1
        is obsolete|                            |

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
Created attachment 13844
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13844&action=edit
A fixed patch

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[Bug dynamic-link/28656] LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28656

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com

--- Comment #3 from Florian Weimer <fweimer at redhat dot com> ---
Comment on attachment 13844
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13844
A fixed patch

This has impact on an unknown number of other things.

I think we should something like <dl-mmap-object.h> that provides a mmap that
is only used for mapping objects, and change dl-map-segments.h to use that. The
PROT_EXEC kludge is probably there for JIT support. So we'd perhaps need both.

Is it really necessary to carry this forward? I think we added it for Xeon Phi,
and that's really very much discontinued by now.

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[Bug dynamic-link/28656] LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28656

--- Comment #4 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Florian Weimer from comment #3)
> 
> Is it really necessary to carry this forward? I think we added it for Xeon
> Phi, and that's really very much discontinued by now.

I am OK to drop it entirely.

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[Bug dynamic-link/28656] LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28656

--- Comment #5 from Florian Weimer <fweimer at redhat dot com> ---
(In reply to H.J. Lu from comment #4)
> (In reply to Florian Weimer from comment #3)
> > 
> > Is it really necessary to carry this forward? I think we added it for Xeon
> > Phi, and that's really very much discontinued by now.
> 
> I am OK to drop it entirely.

Let's do that, then. It's presence is confusing.

Would you be able to send a patch? Thanks.

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[Bug dynamic-link/28656] LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28656

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |hjl.tools at gmail dot com

--- Comment #6 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Florian Weimer from comment #5)
> (In reply to H.J. Lu from comment #4)
> > (In reply to Florian Weimer from comment #3)
> > > 
> > > Is it really necessary to carry this forward? I think we added it for Xeon
> > > Phi, and that's really very much discontinued by now.
> > 
> > I am OK to drop it entirely.
> 
> Let's do that, then. It's presence is confusing.
> 
> Would you be able to send a patch? Thanks.

Sure.

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[Bug dynamic-link/28656] LD_PREFER_MAP_32BIT_EXEC no longer works due to binutils changes

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28656

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |2.35
            Version|unspecified                 |2.35
         Resolution|---                         |FIXED

--- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> ---
commit ea5814467a02c9d2d7608b6445c5d60e2a81d3ee
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Dec 10 13:00:09 2021 -0800

    x86-64: Remove LD_PREFER_MAP_32BIT_EXEC support [BZ #28656]

    Remove the LD_PREFER_MAP_32BIT_EXEC environment variable support since
    the first PT_LOAD segment is no longer executable due to defaulting to
    -z separate-code.

    This fixes [BZ #28656].

    Reviewed-by: Florian Weimer <fweimer@redhat.com>

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