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Richard Yao e853ba3519 Cleanup linking
I noticed during code review of zfsonlinux/zfs#4385 that the author of a
commit had peppered the various Makefile.am files with `$(TIRPC_LIBS)`
when putting it into `lib/libspl/Makefile.am` should have sufficed. Upon
further examination, it seems that he had copied what we do with
`$(ZLIB)`. We also have a bit of that with `-ldl` too.  Unfortunately,
what we do is wrong, so lets fix it to set a good example for future
contributors.

In addition, we have multiple `-lz` and `-luuid` passed to the compiler
because each `AC_CHECK_LIB` adds it to `$LIBS`. That is somewhat
annoying to see, so we switch to `AC_SEARCH_LIBS` to avoid it.  This is
consistent with the recommendation to use `AC_SEARCH_LIBS` over
`AC_CHECK_LIB` by autotools upstream:

https://www.gnu.org/software/autoconf/manual/autoconf-2.66/html_node/Libraries.html

In an ideal world, this would translate into improvements in ELF's
`DT_NEEDED` entries, but that is not the case because of a couple of
bugs in libtool.

The first bug causes libtool to overlink by using static link
dependencies for dynamic linking:

https://wiki.mageia.org/en/Overlinking_issues_in_packaging#libtool_issues

The workaround for this should be to pass `-Wl,--as-needed` in
`LDFLAGS`. That leads us to the second bug, where libtool passes
`LDFLAGS` after the libraries are specified and `ld` will only honor
`--as-needed` on libraries specified before it:

https://sigquit.wordpress.com/2011/02/16/why-asneeded-doesnt-work-as-expected-for-your-libraries-on-your-autotools-project/

There are a few possible workarounds for the second bug. One is to
either patch the compiler spec file to specify `-Wl,--as-needed` or pass
`-Wl,--as-needed` via `CC` like `CC='gcc -Wl,--as-needed'` so that it is
specified early. Another is to patch ltmain.sh like Gentoo does:

https://gitweb.gentoo.org/repo/gentoo.git/tree/eclass/ELT-patches/as-needed

Without one of those workarounds, this cleanup provides no benefit in
terms of `DT_NEEDED` entry generation. It should still be an improvement
because it nicely simplifies the code while encouraging good habits when
patching autotools scripts.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4426
2016-03-18 13:31:11 -07:00
cmd Cleanup linking 2016-03-18 13:31:11 -07:00
config Cleanup linking 2016-03-18 13:31:11 -07:00
contrib Activate LVM volume groups before looking for zpools. 2015-12-18 13:46:23 -08:00
etc Add support for alpine linux 2016-03-08 13:19:53 -08:00
include Add the ZFS Test Suite 2016-03-16 13:46:16 -07:00
lib Cleanup linking 2016-03-18 13:31:11 -07:00
man Require libblkid 2016-03-09 10:39:22 -08:00
module Illumos 6681 - zfs list burning lots of time in dodefault() via dsl_prop_* 2016-03-15 18:46:44 -07:00
rpm Add the ZFS Test Suite 2016-03-16 13:46:16 -07:00
scripts Add the ZFS Test Suite 2016-03-16 13:46:16 -07:00
tests Disable zpool_add_004_pos test case 2016-03-17 09:56:18 -07:00
udev Support parallel build trees (VPATH builds) 2015-07-17 13:42:51 -07:00
.gitignore Ignore *.{deb,rpm,tar.gz} files in the top directory. 2013-04-24 16:18:59 -07:00
.gitmodules Add zimport.sh compatibility test script 2014-02-21 12:10:31 -08:00
AUTHORS Add a missing > to AUTHORS 2014-09-02 14:18:53 -07:00
autogen.sh build: do not call boilerplate ourself 2013-04-02 10:55:20 -07:00
configure.ac Add the ZFS Test Suite 2016-03-16 13:46:16 -07:00
copy-builtin Fix --enable-linux-builtin 2015-12-02 07:54:32 -08:00
COPYRIGHT Update ZED copyright boilerplate 2015-05-11 15:07:00 -07:00
DISCLAIMER Fix minor typos and update marketing copy. 2013-03-21 12:51:06 -07:00
Makefile.am Add the ZFS Test Suite 2016-03-16 13:46:16 -07:00
META Tag zfs-0.6.5 2015-09-11 11:16:38 -07:00
OPENSOLARIS.LICENSE Add CDDL license file 2008-12-01 14:49:34 -08:00
README.markdown Fix minor typos and update marketing copy. 2013-03-21 12:51:06 -07:00
TEST Add the ZFS Test Suite 2016-03-16 13:46:16 -07:00
zfs-script-config.sh.in Add the ZFS Test Suite 2016-03-16 13:46:16 -07:00
zfs.release.in Move zfs.release generation to configure step 2012-07-12 12:22:51 -07:00

Native ZFS for Linux!

ZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the Illumos community.

ZFS on Linux, which is also known as ZoL, is currently feature complete. It includes fully functional and stable SPA, DMU, ZVOL, and ZPL layers.

Full documentation for installing ZoL on your favorite Linux distribution can be found at: http://zfsonlinux.org