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11.2 Creating modules that may be
This file documents GNU Libtool, a script allowing package developers to offer generic shared library support. This edition documents version 2.4.6.
See Reporting bugs, for information about how to report difficulties with GNU Libtool.
How libtool s look at libraries differs from the others.
Example of employing libtool to make libraries.
Using libtool a highly effective packages.
Using libtool and not using a C compiler.
Using library interface versions.
Tips for library interface design.
Libraries that be determined by other libraries.
ing libtool-created libraries.
Libtool s trace interface.
When libtool doesn t are advertised.
Information utilized by the libtool maintainer.
Why does GNU need to have a libtool?
The issues that need to be addressed.
How people have solved these problems.
Learning from past difficulties.
Compiling object files for libraries.
Creating libraries from object files.
Linking object files against libtool libraries.
Running GDB on libtool-generated programs.
Making libraries accessible to users.
Making programs on the market to users.
When shared libraries aren't wanted.
Wrapper executables for most platforms.
Creating library object files.
Generating executables and libraries.
Debugging libtool-generated programs.
Making libraries and executables public.
Completing a library installation.
Removing installed executables and libraries.
Removing uninstalled executables and libraries.
Autoconf macros exported by libtool.
Automatically supporting libtool.
Configuring libtool for any host system.
What files to distribute along with your package.
Sometimes shared libraries are a pain.
Platform-specific notes for configuration.
Autoconf automates LTLIBOBJS generation.
What are library interfaces?
Libtool s versioning system.
Changing version information before releases.
Breaking binary compatibility for aesthetics.
How to post portable include files.
Creating dlopenable objects and libraries.
Dlopening that works well on static platforms.
Using dlopenable modules in libraries.
Unresolved issues that need your attention.
How to make use of libltdl with your programs.
Registering callbacks for multi-thread safety.
Associating data with loaded modules.
Creating user defined module loaders.
How to distribute libltdl using your package.
How to report complications with libtool.
The belongings in the old test suite.
What to complete when a test fails.
How to port libtool to new systems.
When libtool was last tested.
Information about different library systems.
Configuration information that libtool uses.
Making libtool maintainership easier.
Finding details.
Creating object files from source files.
Binding object files together.
Removing duplicate dependent libraries.
Programs that can cause static archives.
Issues that arise when cross compiling.
Converting file names between platforms.
In earlier times, should you be a source code package developer and wished to take advantage of the power of shared libraries, you needed to post custom support code per platform what is the best your package ran. You also needed to design a configuration interface in order that the package installer could choose what type of libraries were built.
GNU Libtool simplifies your work by encapsulating the platform-specific dependencies, as well as the user interface, in one script. GNU Libtool is designed in order for the complete functionality of every host type is accessible via a generic interface, but nasty quirks are hidden from your programmer.
GNU Libtool s consistent interface is reassuring users don t have to read obscure documentation to get their favorite source package build shared libraries. They just run your package
script or equivalent, and libtool does all of the dirty work.
There are a few examples throughout this document. All assume precisely the same environment: we want to make a library,
could certainly be a shared library, a static library, or both whatever can be obtained on the host system, provided that libtool continues to be ported with it.
This chapter explains the initial design philosophy of libtool. Feel free to skip to another chapter, unless you are serious about history, or want to create code to give libtool inside a consistent way.
Why does GNU have to have a libtool?
The conditions that need to be addressed.
How other individuals have solved these problems.
Learning from past difficulties.
Since early 1995, many different GNU developers have recognized the value of having shared library support with regards to packages. The primary motivation for a real change is always to encourage modularity and reuse of code both conceptually and physically in GNU programs.
Such a requirement means that just how libraries are meant in GNU packages ought to be general, to allow for any library type the package installer may wish. The problem is compounded from the absence of a normal procedure for creating shared libraries on different platforms.
The following sections outline the key issues facing shared library support in GNU, and exactly how shared library support could possibly be standardized with libtool.
The system have to be as elegant as is possible.
The system have to be fully integrated with all the GNU Autoconf and Automake utilities, to ensure that it will be straightforward for GNU maintainers to utilize. However, it must not require this software, in order that it can be utilized by non-GNU packages.
Portability along with other non-GNU architectures and tools is desirable.
The following issues have to be addressed in a reusable shared library system, specifically libtool:
The package installer will be able to control what kind of libraries are created.
It is usually tricky running dynamically linked programs whose libraries haven't been installed.
has to be set properly when it is supported, or programs fail to operate.
The system must operate consistently even on hosts that don t support shared libraries.
The commands required to develop shared libraries varies wildly from host to host. These must be determined at configure time inside a consistent way.
It might not be obvious with the information prefix or suffix a shared library really should be installed. This makes it difficult for
rules, simply because they generally feel that file names are exactly the same from host to host.
The system uses a simple library version number abstraction, making sure that shared libraries may be upgraded available. The programmer ought to be informed tips on how to design the interfaces for the library to increase binary compatibility.
Even before libtool was made, many free software packages built and installed their very own shared libraries. At first, these packages were examined to stop reinventing existing features.
Now it's clear that none of those packages have documented the facts of shared library systems that libtool requires. So, other packages have already been more or less abandoned as influences.
In all fairness, all of the implementations that had been examined deliver the results that they were intended to complete, to get a number of different host systems. However, none these solutions often function well like a generalized, reusable component.
Most were too complex to work with much less modify without understanding just what the implementation does, and in addition they were generally not documented.
The main difficulty is different vendors have different views products libraries are, and not one of the packages that had been examined looked like there was confident enough to pay back on a single paradigm that merely works.
Ideally, libtool would be considered a standard that could be implemented as group of extensions and modifications to existing library systems include them as work consistently. However, it can be not straightforward to convince computer developers to mend their evil ways, and the ones want to make shared libraries right this moment, even on buggy, broken, confused systems.
For this reason, libtool was made as an independent shell script. It isolates the difficulties and inconsistencies in library building that plague
writers by wrapping the compiler suite on different platforms with a frequent, powerful interface.
With luck, libtool is going to be useful to and employed by the GNU community, understanding that the lessons that had been learned in making it is going to be taken up by designers of future library systems.
At first, libtool was made to support an arbitrary variety of library object types. After libtool was ported to more platforms, a different paradigm gradually developed for describing their bond between libraries and programs.
In summary, libraries are programs with multiple places, plus much more formally defined interfaces.
Version 0.7 of libtool was obviously a complete redesign and rewrite of libtool to reflect this new paradigm. So far, it's got proved to be successful: libtool is simpler and even more useful than before.
The easiest way to introduce the libtool paradigm should be to contrast it using the paradigm of existing library systems, with examples from each. It is a different way of thinking, thus it may take some time to absorb, just make sure understand it, the entire world becomes simpler.
It makes little sense to discuss using libtool in your packages til you have seen the actual way it makes your lifestyle simpler. The examples in this particular chapter introduce the primary features of libtool by comparing the normal library building procedure to libtool s operation on two different platforms:
An Ultrix 4.2 platform with only static libraries.
A NetBSD/i386 1.2 platform with shared libraries.
You can follow these examples by yourself platform, utilizing the preconfigured libtool script that has been installed with libtool see Configuring.