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* HACKING (Abstraction layers in libltdl): Rewritten somewhat
for (hopefully) better clarity.
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Gary V. Vaughan
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@ -1,3 +1,8 @@
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2007-03-28 Gary V. Vaughan <gary@gnu.org>
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* HACKING (Abstraction layers in libltdl): Rewritten somewhat
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for (hopefully) better clarity.
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2007-03-26 Gary V. Vaughan <gary@gnu.org>
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The stamp-vcl file rules caused non-gnu make programs to rerun
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147
HACKING
147
HACKING
@ -287,71 +287,23 @@ yyyy-mm-dd Name of Author <email@address> (tiny change)
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* The libltdl API uses a layered approach to differentiate internal and
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external interfaces, among other things. To keep the abstraction
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consistent, files in a given layer may only use APIs from files in the
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lower layers. The exception to this is lt__glibc.h which serves a
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dual purpose, as explained later.
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lower layers. The ASCII art boxes below represent this stack, from
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top to bottom...
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* At the bottom of the stack we have the system abstraction layer,
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which tries to smooth over the cracks where there are differences
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between host systems and compilers. config.h is generated at
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configure time and is not installed; lt_system.h is an installed
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file and cannot use macros from config.h:
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lt_system.h ../config.h
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* Next up is the libc abstraction layer, which provides a uniform api
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to various system libc interfaces that differ between hosts supported
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by libtool. Typically, the files that implement this layer begin:
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#if defined(LT_CONFIG_H)
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# include LT_CONFIG_H
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#else
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# include <config.h>
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#endif
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#include "lt_system.h"
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Or if they are installed headers that must work outside the libtool
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source tree, simply:
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#include <libltdl/lt_system.h>
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This layer's interface is defined by files that are usually named with
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a leading `lt__':
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,------------. ,-----------. ,------. ,-------.
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|lt__dirent.h| |lt__alloc.h| |argz.h| |slist.h|
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+------------+ +-----------+ +------+ +-------+
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|lt__dirent.c| |lt__alloc.c| |argz.c| |slist.c|
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`------------' `-----------' `------' `-------'
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The exceptions here are argz.h and slist.h which are used
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independently of libltdl in other projects.
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* There is also a sub-layer that can be used either by the headers that
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implement it, in which case its function is to avoid namespace clashes
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when linked with the GNU C library; Or it can be included by code that
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wants to program against a glibc like interface, where it also serves
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the function of pulling in all the glibc-like functionality used by
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libltdl from a single:
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#include <libltdl/lt__glibc.h>
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It consists of the single file:
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lt__glibc.h
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* The next layer are the subsystems of the exported libltdl API, which
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are defined by files that are named with a leading `lt_' (no double
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underscore!):
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,----------. ,-------------.
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|lt_error.h| |lt_dlloader.h|
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+----------+ +-------------+
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|lt_error.c| |lt_dlloader.c|
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`----------' `-------------'
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* But first, outside of the stack, there is a convenience header that
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defines the internal interfaces (as evidenced by the `lt__' prefix to
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the filename!) shared between implementation files in the stack, that
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are however not exported to libltdl clients:
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,-------------.
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|lt__private.h|
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`-------------'
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* The top layer of the stack is the libltdl API proper, which includes
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the subsystems automatically:
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the relevant subsystems automatically. Clients of libltdl need only
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invoke:
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#include <ltdl.h>
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,------.
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|ltdl.h|
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@ -359,12 +311,75 @@ yyyy-mm-dd Name of Author <email@address> (tiny change)
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|ltdl.c|
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`------'
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* And finally, there is an additional internal only layer (as evidenced
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by the `lt__' prefix to the filename!) that defines additional
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internal interfaces that are not exported to libltdl clients, but are
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shared between internal files:
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* The next layer is comprised of the subsystems of the exported libltdl
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API, which are implemented by files that are named with a leading `lt_'
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(single underscore!):
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lt__private.h
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,------------v---------------.
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| lt_error.h | lt_dlloader.h |
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+------------+---------------+
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| lt_error.c | lt_dlloader.c |
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`------------^---------------'
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* The next file is used both by the headers that implement it (in which
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case its function is to avoid namespace clashes when linking with the
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GNU C library proper) and is included by code that wants to program
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against a glibc-like interface, in which case it serves to pull in all
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the glibc-like functionality used by libltdl with a simple:
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#include <libltdl/lt__glibc.h>
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It consists of a single file:
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,-----------.
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|lt__glibc.h|
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`-----------'
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* Next to last is the libc abstraction layer, which provides a uniform
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API to various system libc interfaces that differ between hosts
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supported by libtool. Typically, the files that implement this layer
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begin:
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#if defined(LT_CONFIG_H)
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# include LT_CONFIG_H
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#else
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# include <config.h>
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#endif
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#include "lt_system.h"
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Or if they are installed headers that must work outside the libtool
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source tree, simply:
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#include <libltdl/lt_system.h>
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This layer's interface is defined by files that are usually named with
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a leading `lt__':
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,--------------v-------------v------------v--------v---------.
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| lt__dirent.h | lt__alloc.h | lt__strl.h | argz.h | slist.h |
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+--------------+-------------+------------+--------+---------+
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| lt__dirent.c | lt__alloc.c | lt__strl.c | argz.c | slist.c |
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`--------------^-------------^------------^--------^---------'
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(argz.h and slist.h are used independently of libltdl in other projects)
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* At the bottom of the stack we have the system abstraction layer,
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which tries to smooth over the cracks where there are differences
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between host systems and compilers. config.h is generated at
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configure time and is not installed; lt_system.h is an installed
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file and cannot use macros from config.h:
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,-----------.
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|../config.h|
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`-----------'
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,-----------.
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|lt_system.h|
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`-----------'
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* Tacked on the side of this stack, attached via the lt_dlloader.h
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definitions are the various implementation modules for run-time module
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loading: preopen.c, dlopen.c etc.
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10. Licensing Rules
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