Please backport r319105 to 5.0.1: [cmake] Pass -Wl,-z,nodelete on Linux to prevent unloading

[llvmbot]

Bugzilla Link	35446
Resolution	WONTFIX
Resolved on	Aug 28, 2019 07:50
Version	5.0
OS	Linux
Blocks	#33840
Reporter	LLVM Bugzilla Contributor
CC	@llvm-beanz,@zmodem,@tstellar

Extended Description

This has no effect on most of LLVM installs (static & dylib) but it's very important for BUILD_SHARED_LIBS=ON installs as it unbreaks mesa plugins.

commit 937b23b
Author: Michal Gorny mgorny@gentoo.org
Date: Mon Nov 27 23:23:09 2017

[cmake] Pass -Wl,-z,nodelete on Linux to prevent unloading

Prevent unloading shared libraries on Linux when dlclose() is called.
This is necessary since command-line option parsing API relies on
registering the global option instances in the option parser instance
which can be loaded in a different shared library.

Given that we can't reliably remove those options when a library is
unloaded, the parser ends up containing dangling references. Since glibc
has relatively complex library unloading rules, some of the LLVM
libraries can be unloaded while others (including the Support library)
stay loaded causing quite a mayhem. To reliably prevent that, just
forbid unloading all libraries -- it's a very bad idea anyway.

While the issue arguably happens only with BUILD_SHARED_LIBS, it may
affect any library reusing llvm::cl interface.

Based on patch provided Ross Hayward on https://bugs.gentoo.org/617154.
Previously hit by Fedora back in Feb 2016:
https://lists.freedesktop.org/archives/mesa-dev/2016-February/107242.html

Differential Revision: https://reviews.llvm.org/D40459

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319105 91177308-0d34-0410-b5e6-96231b3b80d8

[tstellar]

Hi Chris,

Is this OK to merge?

[tstellar]

This was submitted too late to make it into 5.0.1-rc2, so it won't be in the release unless it is determined to be a critical fix.

[llvm-beanz]

I'm not convinced we should back port this at all. It only happens with BUILD_SHARED_LIBS=On and that option really shouldn't be used for building distributed packages (and is documented as such). For that reason I think the priority of this issue is low.

[zmodem]

This is probably obsolete by now.