Motivation:
cmake supports building executables and shared libraries so that they
may be run directly from the build tree. This is useful as it
simplifies and speeds up development work by allowing code to be tested
immediately after building the binaries; i.e., without any installation
step.
As part of this support, cmake will build libraries and executables so
that the ELF metadata contains either an RPATH (on older/non-Linux
systems) or RUNPATH (on newer/Linux systems) that tells the system's
linker to also look for shared libraries in the build tree. This allows
dynamic link loading to find libraries located within the build tree.
Note that cmake will remove the RPATH or RUNPATH elements by relinking
executables or libraries as part of the 'install' target. Although such
paths are likely harmless if distributed, the presence of the build path
as RPATH/RUNPATH metadata is a potential source of confusion for
developers.
Unlike RPATH, the newer RUNPATH path does not resolve transitive
dependencies. As a specific example, the RUNPATH of 'xrdcp' is used to
resolve the XrdUtils library (libXrdUtils.so), but this xrdcp RUNPATH
path is then not used when XrdUtils wishes to resolve dynamic libraries,
such as XrdSecgsi-5 (libXrdSecgsi-5.so). Instead, the expectation is
that the XrdUtils library itself contains any necessary RUNPATH path.
For this specific example, the XrdUtils library located within the build
tree should contain a RUNPATH path so that it may find XrdSecgsi-5 when
loaded by xrdcp, also located within the build tree.
For the most part, cmake takes care of adding such RUNPATH paths
automatically. When cmake knows a target (e.g., xrdcp) depends on some
other target (XrdUtils) then it adds the corresponding RUNPATH entry in
the build-tree binary. However, cmake does not know that XrdUtils will
load other libraries, so it does not add the corresponding RUNPATH path.
The result is that, although it is currently possible to run programs
like 'xrdcp' and 'xrdfs' directly from the build tree, doing so may not
work as intended. The command may fail (e.g., due to the apparent lack
of GSI authentication support) or the build-tree XrdUtils will use
libraries installed in a standard system location (e.g. /usr/lib), which
may yield spurious results.
Modification:
Add the BUILD_RPATH property to the XrdUtils target, so ensuring the
build-tree XrdUtils library contains the necessary RUNPATH. When
installing, the XrdUtils library will now be relinked (to remove this
RUNPATH).
Note that support for the BUILD_RPATH property was added with cmake
v3.8. The change in this patch has no effect when the code is built
with cmake v3.7 or earlier.
Also recall that cmake will remove this RUNPATH location when
installing. Therefore, the final library is unaffected by this change.
Result:
Commands like 'xrdcp' and 'xrdfs' may now be run from within the
build-tree.
You can view, comment on, or merge this pull request online at:
https://github.com/xrootd/xrootd/pull/1374
-- Commit Summary --
* XrdUtils: add suitable RUNPATH to build-tree library
-- File Changes --
M src/XrdUtils.cmake (1)
-- Patch Links --
https://github.com/xrootd/xrootd/pull/1374.patch
https://github.com/xrootd/xrootd/pull/1374.diff
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