Avoid inflating file sizes needlessly and allow binaries to be stripped #117

rpurdie · 2017-03-07T21:13:04Z

The current approach to changing sections in ET_DYN executables is to move
the INTERP section to the end of the file. +This means changing PT_PHDR to
add an extra PT_LOAD section so that the new section is mmaped into memory
by the elf loader in the kernel. In order to extend PHDR, this means moving
it to the end of the file.

Its documented in BUGS there is a kernel 'bug' which means that if you have holes
in memory between the base load address and the PT_LOAD segment that contains PHDR,
it will pass an incorrect PHDR address to ld.so and fail to load the binary, segfaulting.

To avoid this, the code currently inserts space into the binary to ensure that when
loaded into memory there are no holes between the PT_LOAD sections. This inflates the
binaries by many MBs in some cases. Whilst we could make them sparse, there is a second
issue which is that strip can fail to process these binaries:

$ strip fixincl
Not enough room for program headers, try linking with -N
[.note.ABI-tag]: Bad value

This turns out to be due to libbfd not liking the relocated PHDR section either
(#10).

Instead this patch implements a different approach, leaving PHDR where it is but extending
it in place to allow addition of a new PT_LOAD section. This overwrites sections in the
binary but those get moved to the end of the file in the new PT_LOAD section.

This is based on patches linked from the above github issue, however whilst the idea
was good, the implementation wasn't correct and they've been rewritten here.

Signed-off-by: Richard Purdie richard.purdie@linuxfoundation.org

The current approach to changing sections in ET_DYN executables is to move the INTERP section to the end of the file. +This means changing PT_PHDR to add an extra PT_LOAD section so that the new section is mmaped into memory by the elf loader in the kernel. In order to extend PHDR, this means moving it to the end of the file. Its documented in BUGS there is a kernel 'bug' which means that if you have holes in memory between the base load address and the PT_LOAD segment that contains PHDR, it will pass an incorrect PHDR address to ld.so and fail to load the binary, segfaulting. To avoid this, the code currently inserts space into the binary to ensure that when loaded into memory there are no holes between the PT_LOAD sections. This inflates the binaries by many MBs in some cases. Whilst we could make them sparse, there is a second issue which is that strip can fail to process these binaries: $ strip fixincl Not enough room for program headers, try linking with -N [.note.ABI-tag]: Bad value This turns out to be due to libbfd not liking the relocated PHDR section either (NixOS#10). Instead this patch implements a different approach, leaving PHDR where it is but extending it in place to allow addition of a new PT_LOAD section. This overwrites sections in the binary but those get moved to the end of the file in the new PT_LOAD section. This is based on patches linked from the above github issue, however whilst the idea was good, the implementation wasn't correct and they've been rewritten here. Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

probonopd · 2017-03-07T21:57:45Z

Fixing stripping would indeed be very valuable. Thanks!

domenkozar · 2017-03-14T12:47:35Z

@edolstra

EvenOldridge · 2017-03-24T17:12:09Z

I'd love to see this committed as well. Right now the numpy build process uses this and stripping binaries is essential for aws lambda deployment.

edolstra · 2017-04-24T09:40:31Z

Thanks, merged!

Older versions of patchelf (including the latest release, 0.9) can render binaries unable to be stripped. Provided strip only replaces the input binary if it is successful, we can safely hide and ignore this error. See NixOS/patchelf#117

Note that we strip the user program before modifying it with patchelf. This avoids the issue where older versions of patchelf (including the latest release, 0.9) can render binaries unable to be stripped. See NixOS/patchelf#117

zeerd · 2017-08-23T03:56:17Z

was this issue closed?

I met this today in the 0.9 version.

arch:x86_64

added: sorry, i found this fixed after 0.9 release. jusr ignore this.

rpurdie · 2017-08-23T07:34:53Z

There was a bug in my change which #127 addresses and may help.

Sometimes patchelf failed to work because of bug: * NixOS/patchelf#117 * https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903396 Signed-off-by: Yauhen Artsiukhou <jsirex@gmail.com>

Update patchelf to current git version The current version fixes a bug which broke the ability to strip binaries with debug symbols: NixOS/patchelf#117 With the former version of patchelf, I would get "not enough room for program headers, try linking with -N" when trying to strip the binaries. This patch brings patchelf in sync with the commit 27ffe8ae871e7a186018d66020ef3f6162c12c69 of patchelf's git repository. Also update patchelf's build process to match the logic in upstream's automake files (thanks to Frédéric Bonnard for the patch to properly use getconf PAGESIZE). Bug: https://bugreports.qt.io/browse/PYSIDE-740 Last-Update: 2018-07-09 Gbp-Pq: Name update-patchelf.patch

EvenOldridge mentioned this pull request Mar 24, 2017

Option to strip binaries generated by auditwheel pypa/auditwheel#63

Closed

edolstra merged commit c4deb5e into NixOS:master Apr 24, 2017

darealshinji mentioned this pull request Apr 24, 2017

Section re-ordering confuses strip #10

Closed

This was referenced Apr 28, 2017

Failed to build Numpy (python package) spotify/dh-virtualenv#203

Closed

manylinux1 packages contain unstripped, but unstrippable, shared libraries pypa/manylinux#78

Closed

This was referenced Jun 17, 2017

Patchelf warning JonathonReinhart/staticx#33

Closed

Support stripping binaries to further reduce size JonathonReinhart/staticx#31

Closed

njsmith mentioned this pull request Jun 26, 2017

stripping some manylinux generated files produces broken shared objects pypa/manylinux#119

Closed

lukateras mentioned this pull request Nov 8, 2017

[wip] meson: append new items to the original rpath NixOS/nixpkgs#31228

Closed

8 tasks

xhochy mentioned this pull request Feb 20, 2018

Update multibuild to a version that strips binaries in wheels MacPython/scipy-wheels#25

Closed

jsirex mentioned this pull request Jul 12, 2019

Update patchelf to 0.10 habitat-sh/core-plans#2833

Closed

jvolkman mentioned this pull request Mar 7, 2024

Allocate PHT & SHT at the end of the *.elf file #544

Merged

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Avoid inflating file sizes needlessly and allow binaries to be stripped #117

Avoid inflating file sizes needlessly and allow binaries to be stripped #117

rpurdie commented Mar 7, 2017

probonopd commented Mar 7, 2017

domenkozar commented Mar 14, 2017

EvenOldridge commented Mar 24, 2017

edolstra commented Apr 24, 2017

zeerd commented Aug 23, 2017 •

edited

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rpurdie commented Aug 23, 2017

Avoid inflating file sizes needlessly and allow binaries to be stripped #117

Avoid inflating file sizes needlessly and allow binaries to be stripped #117

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rpurdie commented Mar 7, 2017

probonopd commented Mar 7, 2017

domenkozar commented Mar 14, 2017

EvenOldridge commented Mar 24, 2017

edolstra commented Apr 24, 2017

zeerd commented Aug 23, 2017 • edited Loading

rpurdie commented Aug 23, 2017

zeerd commented Aug 23, 2017 •

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