Fix: Build examples when rpath is stripped from in-build-tree libs

Observed issue
==============

Certain tool chains[1, 2] emit warnings or errors when building the
example applications.

```
make[3]: Entering directory
'/home/xxx/src/efficios/lttng/master/src/lttng-ust/doc/examples/easy-ust'
CC       sample.o
CC       tp.o
CCLD     sample

/usr/bin/ld: warning: liblttng-ust-common.so.1, needed by ../../../src/lib/lttng-ust/.libs/liblttng-ust.so, not found (try using -rpath or -rpath-link)
/usr/bin/ld: warning: liblttng-ust-tracepoint.so.1, needed by ../../../src/lib/lttng-ust/.libs/liblttng-ust.so, not found (try using -rpath or -rpath-link)
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_add_fd_to_tracker'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_after_fork_child'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_common_ctor'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_tp_init'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_tp_probe_register_queue_release'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_cancelstate_disable_pop'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_synchronize_rcu'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_register_thread'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_tp_probe_prune_release_queue'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_cancelstate_disable_push'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_before_fork'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_lock_fd_tracker'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_trace_clock'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_has_sys_membarrier'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_unlock_fd_tracker'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_tp_exit'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_get_cpu_sym'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_common_alloc_tls'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_after_fork_parent'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_delete_fd_from_tracker'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_register'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_reader'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_urcu_gp'
/usr/bin/ld: ../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to `lttng_ust_tp_probe_unregister_queue_release'
collect2: error: ld returned 1 exit status
```

=== Reproducer ===

The easiest way to consistently reproduce this type of build failure
is to perform the following steps:

```
./configure
make -j$(nproc)
find . -iname '*.so' -exec chrpath -d {} \;
make -C doc/examples clean
make -j$(nproc)
```

As the examples are not built with libtool, finding the libraries to
link against depends on the shared objects having an rpath.

E.g.

```
$ chrpath src/lib/lttng-ust/.libs/liblttng-ust.so.1.0.0
src/lib/lttng-ust/.libs/liblttng-ust.so.1.0.0: RUNPATH=/home/xxx/src/efficios/lttng/master/src/lttng-ust/src/lib/lttng-ust-common/.libs:/home/xxx/src/efficios/lttng/master/src/lttng-ust/src/lib/lttng-ust-tracepoint/.libs:/home/xxx/src/efficios/lttng/master/usr/lib
```

The current examples build with `-Wl,-rpath`  for `liblttng-ust`, but
not the dependencies of `liblttng-ust` (which would normally be found
via it's own rpath). If the `rpath` is stripped from
`liblttng-ust.so`, or if the tool chain ignores `rpath` explicitly,
then the build with fail.

In the case of a yocto build environment as in GitHub#61[1], the
following commands reproduced the warnings and the errors seen in the
above test case.

```
git clone git://git.yoctoproject.org/poky && cd poky/
. oe-init-build-env
echo "PACKAGECONFIG:pn-lttng-ust = 'examples'" >>conf/local.conf
bitbake lttng-ust
```

=== Solution ===

Explicitly add library search paths and set linker rpath-link are set
for both the standard and cmake examples. Similar changes were
proposed for each of those parts respectively in GitHub#61[1] and GitHub#63[2].

=== Known issues ===

While the `rpath-link` for the second order library dependencies will
allow the builds to complete, the examples will not work at
runtime even when using `rpath`. From `man ld.so`, the rpaths in an
executable or shared object are only considered for direct
dependencies. Therefore, without setting `LD_LIBRARY_PATH` or
installing the libraries test applications will fail as follows:

```
$ ./doc/examples/easy-ust/sample
./doc/examples/easy-ust/sample: error while loading shared libraries: liblttng-ust-common.so.1: cannot open shared object file: No such file or directory
```

References
==========

[1]: https://github.com/lttng/lttng-ust/pull/61
[2]: https://github.com/lttng/lttng-ust/pull/63

Change-Id: I273ccddd0d0b7a1b57b9e09ddf48d8b5b41e6f8e
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/doc/examples/Makefile.am b/doc/examples/Makefile.am
index aebf63bdf5bf11784d81aec5f767321a9a1d950f..79766ec0de6df2f378333bbf2a24d97f4833c69d 100644 (file)
--- a/doc/examples/Makefile.am
+++ b/doc/examples/Makefile.am
@@ -169,7 +169,10 @@ all-local:
                                CFLAGS='$(CFLAGS)' \
                                AM_CFLAGS='$(AM_CFLAGS)' \
                                LDFLAGS="$(LDFLAGS)" \
-                               AM_LDFLAGS='$(AM_LDFLAGS) -L../../../src/lib/lttng-ust/.libs -Wl,-rpath="$(PWD)/../../src/lib/lttng-ust/.libs/" -Wl,-rpath-link="$(PWD)/../../src/lib/lttng-ust/.libs/"' \
+                               AM_LDFLAGS='$(AM_LDFLAGS) -L../../../src/lib/lttng-ust/.libs -L../../../src/lib/lttng-ust-common/.libs -L../../../src/lib/lttng-ust-tracepoint/.libs \
+                               -Wl,-rpath="$(abs_top_builddir)/src/lib/lttng-ust/.libs/" \
+                               -Wl,-rpath-link="$(abs_top_builddir)/src/lib/lttng-ust-common/.libs/" \
+                               -Wl,-rpath-link="$(abs_top_builddir)/src/lib/lttng-ust-tracepoint/.libs/"' \
                                LTTNG_GEN_TP_PATH="$$rel_src_subdir$(top_srcdir)/tools/" \
                                AM_V_P="$(AM_V_P)" \
                                AM_V_at="$(AM_V_at)" \
@@ -222,10 +225,14 @@ all-local:
                                        CXX="$(CXX)" \
                                        $(CMAKE) \
                                        -DCMAKE_INCLUDE_PATH="$(abs_top_srcdir)/include;$(abs_top_builddir)/include" \
-                                       -DCMAKE_LIBRARY_PATH="$(abs_top_builddir)/src/lib/lttng-ust/.libs" \
+                                       -DCMAKE_LIBRARY_PATH="$(abs_top_builddir)/src/lib/lttng-ust/.libs;$(abs_top_builddir)/src/lib/lttng-ust-common/.libs;$(abs_top_builddir)/src/lib/lttng-ust-tracepoint/.libs" \
                                        -DCMAKE_C_FLAGS="$(AM_CFLAGS) $(CPPFLAGS) $(CFLAGS)" \
                                        -DCMAKE_CXX_FLAGS="$(AM_CXXFLAGS) $(CXXFLAGS) $(CPPFLAGS)" \
-                                       -DCMAKE_EXE_LINKER_FLAGS="$(AM_LDFLAGS) $(LDFLAGS)" \
+                                       -DCMAKE_EXE_LINKER_FLAGS="$(AM_LDFLAGS) $(LDFLAGS) \
+                                       -L../../../src/lib/lttng-ust/.libs -L../../../src/lib/lttng-ust-common/.libs -L../../../src/lib/lttng-ust-tracepoint/.libs \
+                                       -Wl,-rpath=$(abs_top_builddir)/src/lib/lttng-ust/.libs/ \
+                                       -Wl,-rpath-link=$(abs_top_builddir)/src/lib/lttng-ust-common/.libs/ \
+                                       -Wl,-rpath-link=$(abs_top_builddir)/src/lib/lttng-ust-tracepoint/.libs/" \
                                        .. && \
                                $(MAKE) \
                        ) || exit 1; \