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# slibtool: a skinny libtool implementation, written in C
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Kylie McClain |
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`slibtool` is an independent reimplementation of the widely used libtool,
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Kylie McClain |
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written in C. `slibtool` is designed to be a clean, fast, easy-to-use
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Kylie McClain |
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libtool drop-in replacement, and is accordingly aimed at package authors,
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Kylie McClain |
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distro developers, and system integrators. `slibtool` maintains compatibility
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Kylie McClain |
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with libtool in nearly every aspect of the tool's functionality as well as
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semantics, leaving out (or turning into a no-op) only a small number of
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Kylie McClain |
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features that are no longer needed on modern systems.
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Kylie McClain |
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Kylie McClain |
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Being a compiled binary, and although not primarily written for the sake of
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performance, building a package with `slibtool` is often faster than with its
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Kylie McClain |
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script-based counterpart. The resulting performance gain would normally vary
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between packages, and is most noticeable in builds that invoke libtool a large
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number of times, and which are characterized by the short compilation duration
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of individual translation units.
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Kylie McClain |
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## why reimplement libtool?
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Midipix targets use the PE binary format, and so require import library
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integration on the one hand, yet follow ELF naming conventions
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(i.e. libfoo.so.x.y.z) on the other. In consequence, midipix shared
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libraries are not fully supported by existing libtool implementations.
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As an interim solution used for the porting of gcc, a libtool script
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generated by ltmain.sh was hand-edited so that it would correctly produce
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the host's shared libraries as part of the toolchain build process.
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Bypassing the libtool script generated by a package's ltmain.sh requires
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overriding the `LIBTOOL` variable as part of invoking `make(1)`. In that
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sense, and unless midipix support is added to every single ltmain.sh in
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every single package that uses autotools, it does not truly matter whether
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the surrogate libtool that one chooses be a script, a program written in C,
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or something else.
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At the time of this writing, an average libtool script consists of about
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`10K lines of code` with `several hundred case-esac statements` and a similar
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number of `if-then blocks`. In view of the length of the generated script,
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and in light of its challenging logic and overall complexity, a rewrite of
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the tool in C seemed to be the right choice not only with respect to quality,
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readability, and anticipated performance, but also in terms of development
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effort, ease of customization, and long-term maintenance.
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## Requirements for building slibtool
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Kylie McClain |
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- a C toolchain, consisting of
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- a C compiler such as gcc, clang, or [cparser];
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- the compiler should support -std=c99;
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- the system's libc should support -D_XOPEN_SOURCE=600.
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## Usage
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With most packages, simply adding `LIBTOOL=slibtool` to the `make` invocation
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should suffice. To have `slibtool` operate in debug mode (outputting a colorized
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raw argument vector), use `LIBTOOL=dlibtool` instead, or alternatively add
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`--debug` to the libtool flags inside of your Makefile.
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### Corner cases
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Some programs which make heavy use of recursive `make` are known to drop the
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`LIBTOOL` value at some point in the process, and as such you may additionally
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need to export the environment variable; `export MAKE="make LIBTOOL=slibtool"`.
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Kylie McClain |
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`slibtool` additionally installs two symlinks that are the equivalent of
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`-disable-shared` and `-disable-static`, named `slibtool-static` and
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`slibtool-shared`, respectively. These symlinks should be used when building
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Kylie McClain |
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packages that have the above switches hard-coded into the generated libtool
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script; two examples of such packages are `binutils` and `gdb`, which both
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have shared library builds disabled by default. A quick way to determine
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whether this invocation form is appropriate with a specific package is to
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run `./libtool --features` from the build directory, then check whether the
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output has either shared or static library builds disabled. When slibtool
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is invoked as a basic tool (i.e. slibtool, dlibtool, etc.), then building
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of both a shared library and a static archive is enabled by default.
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Kylie McClain |
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## Differences from GNU libtool
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While `slibtool` aims to be compatible with all common usages of libtool at the
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build system level, there exist several differences at the implementation level
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that should be noted.
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Kylie McClain |
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- `.la wrappers` are always generated, but by default are never installed;
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`.la wrappers` contain key information that is provided to libtool when
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generating a shared library or static archive, and which is needed when
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passing the archive or library as an input argument in .la form to the
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compiler driver in subsequent link steps. Since `slibtool` is entirely
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independent of the above wrappers with respect to its own functionality,
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and given its announced goal to remain compatible with the script-based
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libtool as much as possible, `slibtool`'s behavior is to always produce
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`.la wrappers` on the one hand, yet fully ignore their content on the
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other.
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Despite their internal nature, installed .la wrappers are often [ab]used
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in strange and mysterious ways by distro-related tools other than libtool
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itself. For the sake of distributions that depend on the aforementioned
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wrappers, slibtool comes with three special symlinks named `clibtool`,
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`clibtool-shared`, and `clibtool-static`, respectively. The `'c'` in
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`clibtool` stands for `compatible`, and accordingly indicates an end-user's
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preference towards perfect emulation of legacy behavior.
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- `-rpath` argument values are passed to the compiler and linker as needed only;
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`-rpath` is often [mis]used by libtool to add redundant paths to a program's
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linker search path. When using slibtool, `-rpath` argument values are only
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forwarded to the compiler and linker when pointing to non-default linker
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directories, and are accordingly filtered out when pointing to default
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library locations (i.e. `/usr/lib`, `/lib`, and so on).
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- no-ops
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- `-R`, which adds a path to the generated program's run-time search path;
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this switch is currently not needed, and is accordingly ignored.
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- `-export-symbols`, which exports symbols listed in a given file, and
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`-export-symbols-regex`, which exports symbols matching a regex;
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both are unimplemented because similar functionality has long been
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provided by the compiler or toolchain; `gcc` has supported setting ELF
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visibility since v4.0, for instance, and PE import library support is
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provided by slibtool via the --output-def linker switch and a subsequent
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invocation of dlltool.
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- `-no-install`, which considers the executable wrapper to be optional;
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this switch is not needed on modern systems, and is accordingly ignored.
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- No `libltdl`.
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libltdl is nowadays no longer needed; it serves to provide a `dlopen()`
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functionality on systems which do not offer it, i.e. HP-UX and BeOS,
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however since neither HP-UX nor BeOS is currently supported by slibtool,
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there exists no urgent need to provide equivalent functionality.
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## Development
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Major changes to slibtool should be discussed on [#midipix] prior to pursuing
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a considerable effort, and patches should be sent, gpg-signed, to the project
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maintainer; before hacking on slibtool, please take a moment of your time and
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read the [CONTRIB] document.
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As you finalize your changes to the code, please consider building at least
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once with `cparser` as the compiler. cparser is excellent at catching logical
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errors and semantic flaws, and as of the time of this writing is capable of
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spotting bugs that go unnoticed by other major compilers. For a few examples
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of such hidden bugs, see commits [94d109f], [1142bf2], and [55c95a8].
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## License
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`slibtool` is distributed under a permissive [MIT license].
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[MIT license]: http://git.midipix.org/cgit.cgi/slibtool/tree/COPYING.SLIBTOOL
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[libltdl]: https://www.gnu.org/software/libtool/manual/html_node/Using-libltdl.html#Using-libltdl
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[dlopen()]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/dlopen.html
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[CONTRIB]: http://git.midipix.org/cgit.cgi/slibtool/tree/CONTRIB
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[libtool]: https://www.gnu.org/software/libtool/
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[#midipix]: irc://irc.freenode.net/#midipix
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[cparser]: http://pp.ipd.kit.edu/git/cparser/
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[94d109f]: http://git.midipix.org/cgit.cgi/slibtool/commit/?id=94d109fa418c024c214a50d645624e2e2935e6d1
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[1142bf2]: http://git.midipix.org/cgit.cgi/slibtool/commit/?id=1142bf2e13f411cf967c1ed8b4060d7829eb13bb
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[55c95a8]: http://git.midipix.org/cgit.cgi/slibtool/commit/?id=55c95a829928ae9f053678a58a2145276cad9c08
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