freebsd-nq/lib/libzfs
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
..
.gitignore Add a pkgconfig file 2014-08-28 07:59:43 -07:00
libzfs_changelist.c Remove ZFC_IOC_*_MINOR ioctl()s 2013-12-16 09:15:57 -08:00
libzfs_config.c Fix zpool iostat bandwidth/ops calculation 2016-03-08 17:43:33 -08:00
libzfs_core.pc.in Add a pkgconfig file 2014-08-28 07:59:43 -07:00
libzfs_dataset.c Illumos 4953, 4954, 4955 2016-01-15 15:38:36 -08:00
libzfs_diff.c Illumos 4448 - zfs diff misprints unicode characters 2016-02-05 13:04:58 -08:00
libzfs_fru.c cstyle: Resolve C style issues 2013-12-18 16:46:35 -08:00
libzfs_graph.c Illumos #3464 2013-09-04 16:01:24 -07:00
libzfs_import.c Updated paths to scan when importing zpool(s) 2016-03-09 10:41:23 -08:00
libzfs_iter.c Illumos 5427 - memory leak in libzfs when doing rollback 2015-07-10 12:09:32 -07:00
libzfs_mount.c Illumos 4953, 4954, 4955 2016-01-15 15:38:36 -08:00
libzfs_pool.c Add -gLp to zpool subcommands for alt vdev names 2016-02-25 11:58:39 -08:00
libzfs_sendrecv.c Illumos 5960, 5925 2016-01-08 15:08:19 -08:00
libzfs_status.c Read spl_hostid module parameter before gethostid() 2015-02-04 16:44:53 -08:00
libzfs_util.c Add the ZFS Test Suite 2016-03-16 13:46:16 -07:00
libzfs.pc.in Add a pkgconfig file 2014-08-28 07:59:43 -07:00
Makefile.am Cleanup linking 2016-03-18 13:31:11 -07:00