# Guidelines for packaging/building¶

HashDist can be used to build software in many ways. This document describes what the HashDist authors recommend and the helper tools available for post-processing.

## Principles¶

• Build artifacts should be fully relocatable, simply because we can, and it is convenient. In particular it means we can avoid adding complexity (an extra post-processing phase) for binary artifacts.
• It should be possible to use the software with as few environment variable modifications as possible. I.e., one should be able to do path/to/profile/bin/program without any changes to environment variables at all, and a typical setup would only modify $PATH. ## Relocatable artifacts¶ Relocatability is something that must be dealt with on a case-by-case basis. ### Artifact relative references¶ For relative artifacts to work (at least without serious patching of all programs involved...), it is currently necesarry to insist that all build artifacts involved are in the sub-directory/partition, so that relative paths such as ../../../python/34ssdf32/lib/.. remain valid. Note Considering the future: If multiple artifact dirs are needed, a possibility for splitting up build artifact repositories would be to symlink between them at the individual artifact level, say: /site/hit/zlib/afda/... /site/hit/python/fdas/...  And then another artifact directory could contain: /home/dagss/.hit/opt/zlib/afda -> /site/hit/zlib/afda /home/dagss/.hit/opt/python/fdas -> /site/hit/python/fdas /home/dagss/.hit/opt/pymypackage/3dfs/...  Because artifacts should be a DAG this should work well. This could be naturally implemented as whenever a cached build artifact is found on a locally available filesystem, symlink to it. Of course, now /site/hit is not relocatable, but mere rewriting of those symlinks, always at the same level in the filesystem, is a lot more transparent than full post-processing of artifacts. ### Unix: Scripts¶ The shebang lines #!/usr/bin/env interpreter or #!/full/path/to/interpreter are limited and preclude relocatability by themselves. We deal with this by using multi-line shebangs. We want to search for interpreters for scripts as follows: • In the bin-dir of the profile in use (typically, but not always, along-side the script). We define this as: For each symlink in the chain between $0 and the real script file, search upwards towards the root for a file named profile.json. If found, find the interpreter (by its base name) in the bin-subdirectory.
• Otherwise, fall back to the relative path between the real location of the script file and the interpreter’s build artifact. (E.g., for Python, this could work if PYTHONPATH is also set correctly, as may be the case during builds.)

Example: The command:

$hit build-postprocess --shebang=multiline path-or-script  applies the multiline shebang. Test script: #!/tmp/../usr/bin/python """simple example""" print 'Hello world'  Note that shebangs with /usr/bin/* is not processed, so we had to force the tool to kick in using /tmp/../usr/bin/ (because the intention is really just to patch references to other artifacts). Then calling the command above yields: #!/bin/sh # -*- mode: python -*- "true" '''\';r="../../../../usr/bin";i="python";o=pwd;p="$0";while true; do test -L "$p";il=$?;cd dirname "$p";pdir=pwd -P;d="$pdir";while [ "$d" != / ]; do [ -e profile.json ]&&cd "$o"&&exec "$d/bin/$i" "$0" "$@";cd ..;d=pwd -P;done;cd "$pdir";if [ "$il" -ne 0 ];then break;fi;p=readlink $p;done;cd "$r";p=pwd -P;cd "$o";exec "$p/$i" "$0" "$@";exit 127; ''' # end multi-line shebang, see hashdist.core.build_tools __doc__ = """simple example""" print 'Hello world' # vi: filetype=python  This file is executable both using Python 2.x or a POSIX shell. See the code of hashdist.core.build_tools for the shell script in a non-compacted form with comments. Note the r and i variables; ../../../../usr/bin was simply the relative path between the example script and /usr/bin when the command was run. ### Unix: Dynamic libraries¶ Modern Unix platforms allows binaries to link to dynamic libraries in relative locations by using an RPATH containing the string ${ORIGIN}. See man ld.so (on Linux at least).

Passing this is almost impossible because whenever one uses the configure system it tends to add the absolute RPATH anyway. Also, the contortions one must go through to properly escape the magic string ($ unfortunately being part of it) is build-system specific, for autoconf with libtool it is \$$ORIGIN, where first Make sees $$, and then Bash sees \$.

Fortunately, for Linux there is patchelf and for Mac OS X [another tool].