CODEWITHSUNDEEP
qtshared-librariesld
DJohnson
DJohnson

Reputation: 23

ld skips shared library

I am trying to deploy a Qt application by providing the Qt libraries as shared libraries in a directory and pointing ld to them using LD_LIBRARY_PATH. This works for all Qt libraries such as libQt5Network or libQt5Gui, but not for libQt5Core which is somehow not found and the system version is used instead.

Using LD_DEBUG=all I can see that ld tries the file which exists, but skips it

  3705: file=libQt5Core.so.5 [0];  needed by ./app.bin [0]
  3705: find library=libQt5Core.so.5 [0]; searching
  3705:  search path=/home/user/app/lib:/usr/lib64/tls/x86_64/x86_64:/usr/lib64/tls/x86_64:/usr/lib64/tls/x86_64:/usr/lib64/tls:/usr/lib64/x86_64/x86_64:/usr/lib64/x86_64:/usr/lib64/x86_64:/usr/lib64     (LD_LIBRARY_PATH)
  3705:   trying file=/home/user/app/lib/libQt5Core.so.5 <- this file exists
  3705:   trying file=/usr/lib64/tls/x86_64/x86_64/libQt5Core.so.5
  3705:   trying file=/usr/lib64/tls/x86_64/libQt5Core.so.5
  3705:   trying file=/usr/lib64/tls/x86_64/libQt5Core.so.5
  3705:   trying file=/usr/lib64/tls/libQt5Core.so.5
  3705:   trying file=/usr/lib64/x86_64/x86_64/libQt5Core.so.5
  3705:   trying file=/usr/lib64/x86_64/libQt5Core.so.5
  3705:   trying file=/usr/lib64/x86_64/libQt5Core.so.5
  3705:   trying file=/usr/lib64/libQt5Core.so.5

Both libQt5Core.so.5 and app.bin are 64 bit elf.

Is there any way to find out why ld rejects the file?

Upvotes: 1

Views: 240

Answers (2)

Ruslan
Ruslan

Reputation: 19120

The other answer is correct. Just in case the link there gets broken, here's what happened in my case and how I fixed it.

I was running an older kernel, version 3.10, on a system where Qt5 was installed. One of the libraries – namely, libQt5Core.so.5.11.0, has an ELF section .note.ABI-tag, which specifies that the library was compiled for kernel 3.17.0. Presence of this section can be seen via e.g.

objdump -sj .note.ABI-tag /path/to/library.so

And the fact that it's compiled for a newer kernel is revealed by file, with the hard to notice note, "for GNU/Linux 3.17.0", near the end of its output. In my case it was:

/opt/qt511/lib/libQt5Core.so.5.11.0: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 3.17.0, BuildID[sha1]=df5f7e933899d1ff629145ab7ca35b2f9bc41843, stripped

So the fix in my case was to run

strip --remove-section=.note.ABI-tag /path/to/library.so

which removed this section and allowed the library to load.

Beware though, that if you do this, you explicitly break the assumptions the library build system may have used, so things may break. In my case they didn't, though.

Upvotes: 1

DJohnson
DJohnson

Reputation: 23

Solution is here: https://github.com/Microsoft/WSL/issues/3023

The library contains an ABI note which can be removed using strip to make ld accept the library.

Upvotes: 1

Related Questions