path: root/Build/source/doc/build.texi

@ifnottex
@macro eTeX
e-@TeX{}
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@node Build System
@chapter The @TL{} Build System

@cindex build system
@cindex the @TL{} build system

The @TL{} build system has been redesigned in 2009, using Autoconf,
Automake, and Libtool.  Thus @* @ @ @ @code{configure && make && make check
&& make install} @* or the more or less equivalent top-level @code{Build}
script suffice to build and install the @TL{} programs, where @code{make
check} performs various test of the generated programs that are not
necessary but strongly recommend.

The main components of the @TL{} build system are @TeX{} specific programs
in subdirectories @file{texk/@var{prog}}, utility programs in subdirectories
@file{utils/@var{prog}}, @TeX{} specific libraries in the subdirectories
@file{texk/kpathsea} and @file{texk/ptexenc} used by the @TeX{} specific
programs, and generic libraries in subdirectories @file{libs/@var{lib}}.

The primary design goal is modularity.  Each program and library module (or
package) specifies its own requirements and properties, such as required
libraries, whether an installed (system) version of a library can be used,
configure options to be seen at the top-level, and more.  An explicit list
of all available modules is only kept in one central place.

A second, related goal is to configure and build each library before
configuring any other (program or library) module using that library.  This
allows to check for properties and features of a library built as part of
the @TL{} tree in much the same way as for a system version of that library.

All generic libraries and several programs are maintained independently. 
The corresponding modules use (parts of) the distributed source tree and
document any modifications of that source tree.

All this should simplify upgrading of modules maintained independently
and/or integrating new modules into the @TL{} build system.

@menu
* Prerequisites::               Requirements to Build @TL{}.
* Building and Installing::     Building and Installing @TL{}.
* Source Tree::                 The @TL{} Source Tree.
* Configure Options::           List of all Configure Options.
* Cross Compilation::           Cross Compilation.
* Coding Rules::                Coding Rules for @TL{}.
@end menu

@node Prerequisites
@section Requirements to Build @TL{}

Building the @TL{} programs requires

@itemize @bullet
@item
C and C++ compilers

@item
GNU @command{make}

@end itemize

@noindent and uses the libraries included in the @TL{} source tree.
There are, however, some additional requirements

@itemize @bullet
@item
@file{xindy} requires GNU @command{clisp} and in addition
@command{perl}, @command{latex}, and @command{pdflatex} to build the rules
and/or documentation.

@item
Autodetection of the @TL{} platform name for @file{biber} requires
@command{perl}.

@item
@file{xpdfopen} and @file{xdvik} require X11 headers and libraries (often a
``development'' package, not installed by default).

@item
XeTeX requires an Objective C++ compiler under Mac OS X or otherwise
@file{libfontconfig} (again both headers and library).

@item
Modification of any @code{.y} or @code{.l} source files requires
@file{bison} or @file{flex} to updatete the corresponding C sources.

@item
Modification of any part of the build system (@code{M4} macros,
@file{configure.ac}, @file{Makefile.am}, or their fragments) requires
GNU M4, GNU Autoconf, GNU Automake, and
GNU Libtool to update the generated files.

@end itemize

@noindent Without the required tools modifying such files or building these
programs must avoided, e.g., via @code{--disable-xindy} or
@code{--without-x}.

@node Building and Installing
@section Building and Installing @TL{}

The top-level @file{Build} script can be used to configure and build
everything in a subdirectory (root of the build tree, default @file{Work}),
install everything in an other subdirectory (default @file{inst}), and
finally run @code{make check}.  Several details of this process can be
specified via environment variables and a few leading options; all remaining
arguments (assignments or options) are passed to the @file{configure}
script.  Or one can run @command{configure} and @command{make} in a suitable
empty subdirectory.

Running the top-level @file{configure} script configures just the top-level
and the subdirectories @file{libs}, @file{utils}, and @file{texk}.  Running
@command{make} at the top-level first iterates over all @TeX{} specific
libraries, and then runs @command{make} in @file{libs}, @file{utils}, and
@file{texk} to iterate over all generic libraries, utility programs, and
@TeX{} specific programs.  These iterations consist of two steps: @* (1) For
each library or program module not yet configured run @command{configure}
adding the configure option @code{--disable-build} if the module need not be
built or otherwise run @command{make all}.  @* (2) For each library or
program module that must be built run @command{make} for the selected
target(s): @code{default} or @code{all} to (re-)build, @code{check} to run
tests, @code{install} etc.

Running the top-level @command{make} a second time iterates again over all
library and program modules and rebuild rebuild as necessary due to modified
source files.

In case configuring or building a module fails, one could fix the problem,
remove the subdirectory for the module from the build tree, and rerun the
top-level @command{make} (or @file{Build} script with @code{--no-clean} as
additional first argument).

With the configure option @code{--disable-all-pkgs} all program and library
modules are configured but none of them are built.  The @file{Makefile} for
each such module contains all build rules and dependencies and can be
invoked to build an individual program or library and causes to first build
any required libraries.  This build "on demand" procedure is used, e.g., in
the @code{luatex} repository to build Lua@TeX{}, essentially from a subset
of the complete @TL{} tree.  Similarly, when, e.g., building @eTeX{} has
been disabled (as by default), one can run @command{make etex} (or
@command{make etex.exe}) in @file{texk/web2c/} to build @eTeX{} (altough
there is no simple way to install @eTeX{}.

The @TL{} build system carefully formulates dependencies as well as make
rules when a tool (such as @command{tangle}, @command{ctangle}, or
@command{convert}) creates several output files.  This allows for parallel
builds (@command{make -j @var{n}} with @var{n}>1 or even @command{make -j})
that can considerably speed up the @TL{} build on multi core systems.  Further
speed up can be achieved by using a configure cache file, i.e., with the
top-level configure option @code{-C}.

The command @command{make dist} (at the top-level) creates a tarball
@file{tex-live-@var{yyyy}-@var{mm}-@var{dd}.tar.xz} from the @TL{} source
tree, whereas @command{make dist-check} also verifies that this tarball can
be used to build and install all of @TL{}.

@subsection Installation Paths

Running @code{make install} (or @code{make install-strip}) installs
executables in @code{@var{bindir}}, libraries in @code{@var{libdir}},
headers in @code{@var{includedir}}, data (including "linked scripts") in
@code{@var{datarootdir}/texmf-dist}, manpages in @code{@var{mandir}}, and
@TeX{} info files in @code{@var{infodir}}.  The values of these directories
are determined by @command{configure} and can be specified explictly as
options such as @code{--prefix=@var{prefix}} or
@code{--bindir=@var{bindir}}; otherwise they are given by their usual
Autoconf defaults

@example
@code{@var{prefix}}                  @code{/usr/local}
@code{@var{exec_prefix}}             @code{@var{prefix}}
@code{@var{bindir}}                  @code{@var{exec_prefix}/bin}
@code{@var{libdir}}                  @code{@var{exec_prefix}/lib}
@code{@var{includedir}}              @code{@var{prefix}/include}
@code{@var{datarootdir}}             @code{@var{prefix}/share}
@code{@var{mandir}}                  @code{@var{datarootdir}/man}
@code{@var{infodir}}                 @code{@var{datarootdir}/info}
@end example

@noindent and modified as follows:

@itemize @bullet
@item
If the option @code{--enable-multiplatform} is given (or implied for a
native @TL{} build), @code{/@var{host}}, i.e., the canonical host name is
appended to @code{@var{bindir}} and @code{@var{libdir}}.

@item
In a native @TL{} build @code{@var{datarootdir}} is set to
@code{@var{prefix}}, @code{@var{mandir}} to
@code{@var{prefix}/texmf-dist/doc/man}, and @code{@var{infodir}} to
@code{@var{prefix}/texmf-dist/doc/info}.
@end itemize

@noindent The top-level @file{configure} script displays all these
installation paths.

For a native @TL{} build either for the @TL{} DVD or for an additional
platform the contents of @code{@var{bindir}} should be copied to the
directory @code{Master/bin/@var{arch}} of the @TL{} tree where
@code{@var{arch}} is the @TL{} platform name corresponding to canonical host
name @code{@var{host}}, the contents of @code{@var{libdir}} and
@code{@var{includedir}} can be discarded, and everything else should match
files already present in the @TL{} tree.

@subsection Linked Scripts

Quite a few executables are architecture independent Shell, Perl, or other
scripts.  Some of them are maintained as part of the @TL{} source tree, but
most are maintained elsewhere with copies under
@file{texk/texlive/linked_scripts}.  They are installed under
@code{@var{datarootdir}/texmf-dist/scripts}; for Unix-like systems there is
a symbolic link pointing, e.g., from @code{@var{bindir}/ps2eps} to
@code{@var{datarootdir}/texmf-dist/scripts/ps2eps/ps2eps.pl} whereas for
Windows @code{@var{bindir}/ps2eps.exe} is a copy of a small standard binary
serving the same purpose.  One reason for all this is to avoid having many
copies for the same script, but most importantly this allows to invoke the
same Perl or other script under Windows.

@subsection Distro Builds

Although they use the same code base, building for a @TL{} binary distribution
as shipped by the user groups may be quite different from a 'distro' build
for, e.g., some kind of Linux distribution, a *Bsd or Mac OS X port, or
similar.

While a @TL{} binary distribution uses shared libraries (@file{libc},
@file{libm}, X11 libraries, and @file{libfontconfig}) only when absolutely
necessary, a distro might use as many shared libraries as possible,
including @TeX{} specific libraries such as @file{libkpathsea}.  In addition
the installation paths will, in general, be quite different.

@subsubsection Configuring for a Distro

For a distro build you must use @* @ @ @
@code{--disable-native-texlive-build} @* and should use @* @ @ @
@code{--with-banner-add=/@var{SomeDistro}} @* to identify your distro.  You
may specify @* @ @ @ @code{--enable-shared} @* to build shared @TeX{}
specific libraries and might add @* @ @ @ @code{--disable-static} @* to not
build the static ones.  You would like to use @* @ @ @
@code{--with-system-@var{lib}} for as many libraries as possible and may
then have to add @code{--with-@var{lib}-includes=@var{dir}} and/or
@code{--with-@var{lib}-libdir=@var{dir}}.

You should specify @* @ @ @  @code{--prefix=/usr} or perhaps
@code{--prefix=/opt/TeXLive} @* and may have to add @* @ @ @
@code{--libdir=\$@{exec_prefix@}/lib64} @* for 64bit bi-arch (Linux)
systems.

To make a usable @TeX{} installation, you need (thousands of) support files
in addition to the binaries that are built and installed here.  The support
files are maintained completely independently.  The best basis for dealing
with them is the @TL{} (plain text) database and/or the @TL{} installer.

@node Source Tree
@section The @TL{} Source Tree

The @TL{} source tree is the subtree rooted at @file{Build/source} of the
complete @TL{} tree and contains the sources for all @TL{} executables as
well as @command{make} rules to build and install them together with some of
their support files.

@menu
* Top Levels::                  The Top-Level Directories.
* Library Modules::             Structure of Library Modules.
* Program Modules::             Structure of Program Modules.
* Extending::                   Adding New Modules.
@end menu

@node Top Levels
@subsection The Top-Level Directories

@include build-tools

@noindent These versions should be used to update the generated files (e.g.,
@file{configure} or @file{Makefile.in}) in all or parts of the @TL{} tree
when some of their sources have been changed.  This can be done explicitly
with the top-level @command{reautoconf} script or implicitly by using the
configure option @code{--enable-maintainer-mode}.

The files in the SVN repository are all up to date, but this need
not be reflected by their timestamps.  In order not to run @command{bison},
@command{flex}, or @command{makeinfo} it may be necessary to @command{touch}
the generated (@file{.c}, @file{.h}, or @file{.info}) files.  With
@code{--enable-maintainer-mode} mode it may also be necessary to
@command{touch} first @file{aclocal.m4}, then @file{configure} and
@file{config.h.in} (or @file{c-auto.in}), and finally all @file{Makefile.in}
files.

The files @file{config.guess}, @file{config.sub}, etc.@ for most packages
are kept centrally in @file{build-aux/}, sourced from GNU Gnulib
(@url{http://www.gnu.org/software/gnulib}), which in turn pulls them from
their ultimate upstream source repository.  There are, however, independent
copies in, e.g., @file{libs/freetype2/freetype-*/builds/unix/}, and similar
places.  The @command{reautoconf} script does not take care of those, but a
@TL{} cron job keeps them in sync (nightly).

The subdirectories @file{m4} and @file{am} contain @code{M4} macros and
@file{Makefile.am} fragments respectively, all of them used in many places.

The file @file{m4/kpse-pkgs.m4} contains lists of all program and library
modules; missing modules are, however, silently ignored.  Each such module
contributes fragments defining its capabilities and requirements to the
@file{configure.ac} scripts at the top-level and in the subdirectiories
@file{libs}, @file{utils}, and @file{texk}.  The fragments from program
modules supply configure options to disable or enable building them, those
from library modules specify if an installed (system) version of that
library can be used.  This decides which modules need to be built, although
all modules must be configured for the benefit of @file{make} targets such
as @code{dist} or @code{distcheck}.

The subdirectory @file{extra} contains things which are not part of the TeX
Live build, but are present for convenience, e.g., @file{epstopdf} developed
here or @file{xz} required by the @TL{} installer.

@node Library Modules
@subsection Structure of Library Modules

The structure of library modules is best explained with a few examples.

@subsubsection The @code{png} library in @file{libs/libpng}

This generic library uses the distributed source tree in, e.g.,
@file{libpng-1.5.17} with all modifications recorded in
@file{libpng-1.5.17-PATCHES/*}.  The @file{configure.ac} fragment
@file{ac/withenable.ac} contains

@example
KPSE_WITH_LIB([libpng], [zlib])
@end example

@noindent with the module name and indicating the dependency on @code{zlib}. 
A third argument @code{tree} would specify that the library from the @TL{}
tree can not be replaced by a system version.  That not being the case, a
second fragment @file{ac/libpng.ac} contains

@example
KPSE_TRY_LIB([libpng],
             [#include <png.h>],
             [png_structp png; png_voidp io; png_rw_ptr fn;
png_set_read_fn(png, io, fn);])
@end example

@noindent and provides the simple C code

@example
#include <png.h>
int main ()
@{ png_structp png; png_voidp io; png_rw_ptr fn;
  png_set_read_fn(png, io, fn);
  return 0; @}
@end example

@noindent used to verify the usability of a system version.  The similar
macro @code{KPSE_TRY_LIBXX} would provide some C++ code.  These fragments
are included by @file{configure.ac} at the top levels.

A proxy build system (@file{configure.ac}, @file{Makefile.am}, and
@file{include/Makefile.am}) ignores the distributed one and consequently a
few generated files and auxiliary scripts are removed from the distributed
source tree.  The public headers @file{png.h}, @file{pngconf.h}, and
@file{pnglibconf.h} are 'installed' (as symlinks) under @file{include/} in
the build tree exactly as they are for a system version under, e.g.,
@file{usr/include/}.

The module is supplemented by the file @file{m4/kpse-libpng-flags.m4} that
defines the @code{M4} macro @code{KPSE_LIBPNG_FLAGS} used by all modules
depending on this library in their @file{configure.ac} to generate the
@code{make} variables @code{LIBPNG_INCLUDES} for use in @code{CPPFLAGS},
@code{LIBPNG_LIBS} for use in @code{LDADD}, @code{LIBPNG_DEPEND} for use as
dependency, and @code{LIBPNG_RULE} defining @code{make} rules to rebuild the
library.

In addition @file{m4/kpse-libpng-flags.m4} supplies the configure option
@code{--with-system-libpng} and uses @command{pkg-config} to determine the
flags required for the system library.

@subsubsection The @code{zlib} library in @file{libs/zlib}

This generic library is quite analogous to @code{libpng} but does not depend
on any other library.  The file @file{m4/kpse-zlib-flags.m4} supplies the
configure option @code{--with-system-zlib} as well as
@code{--with-zlib-includes} and @code{--with-zlib-libdir} to specify non
standard locations of the @code{zlib} headers and/or library.

@subsubsection The @code{freetype} library in @file{libs/freetype2}

This module uses a wrapper build system with an almost trivial
@file{configure.ac} and with @file{Makefile.am} that invokes
@command{configure} and @command{make} for the distributed source, followed
by @command{make install} with the build tree as destination.  The flags
required for the system library are obtained through
@command{freetype-config}.

@subsubsection The @code{kpathsea} library in @file{texk/kpathsea}

This is one of the @TeX{} specific libraries that are maintained as part of
@TL{}.  Other than the generic libraries they are (static and/or shared)
Libtool libraries and are installed together with the programs.  They are,
however, not part of the @TL{} DVD as distributed by @TeX{} user groups.

It is possible, although quite unusual to specify the configure option
@code{--with-system-kpathsea} in order to use a system version of the
library and it may then be necessary to specify
@code{--with-kpathsea-includes} and/or @code{--with-kpathsea-libdir}.

In addition to @file{ac/withenable.ac} and @file{ac/kpathsea.ac} there is a
third fragment @file{ac/mktex.ac} included by both @file{ac/withenable.ac}
and @file{configure.ac} that supplies configure options such as
@code{--enable-mktextfm-default} determining the compile time default
whether or not to run @code{mktextfm} to generate a missing @file{.tfm}
file.  Note, however, that the command line options @code{-mktex=tfm} or
@code{-no-mktex=tfm} for @TeX{}-like engines override this default.

@node Program Modules
@subsection Structure of Program Modules

The structure of program modules is again best explained with a few examples.

@subsubsection The @code{t1utils} package in @file{utils/t1utils}

Once again we use the distributed source tree @file{t1utils-1.37} with
modifications documented in @file{t1utils-1.37-PATCHES/*} and a proxy build
system consisting of @file{configure.ac} and @file{Makefile.am}.  The
fragment @file{ac/withenable.ac} contains

@example
KPSE_ENABLE_PROG([t1utils])
@end example

@noindent specifying the module name without any dependencies and supplies
the configure option @code{--disable-t1utils}.

@subsubsection The @code{xindy} package in @file{utils/xindy}

This module uses the distributed source tree @file{xindy-2.4} with
modifications documented in @file{xindy-2.4-PATCHES/*}, a proxy
@file{configure.ac}, and a wrapper @file{Makefile.am} that descends into
@file{xindy-2.4}.  This requires that the distributed @file{Makefile}s allow
a VPATH build, can handle all targets, and do not refer to
@code{$@{top_srcdir@}} or @code{$@{top_builddir@}}.  The fragment
@code{ac/withenable.ac} contains

@example
KPSE_ENABLE_PROG([xindy], , [disable native])
m4_include(kpse_TL[utils/xindy/ac/xindy.ac])
m4_include(kpse_TL[utils/xindy/ac/clisp.ac])
@end example

@noindent where @code{disable} in the third argument indicates that
@code{xindy} is only built if explicitly enabled by @code{--enable-xindy}
(because it requires @code{clisp}) and @code{native} disallows cross
compilation.  The additional fragments @file{ac/xindy.ac} and
@file{ac/clisp.ac} specify more configure options to be seen at the
top-leved with @file{ac/xindy.ac} also included by @file{configure.ac}.

@subsubsection The @code{xdvik} package in @file{texk/xdvik}

This package is maintained as part of the @TL{} tree with sources in its
top-level and the subdirectory @file{gui}.  The fragment
@code{ac/withenable.ac} contains

@example
dnl extra_dirs = texk/xdvik/squeeze
KPSE_ENABLE_PROG([xdvik], [kpathsea freetype2], [x])
m4_include(kpse_TL[texk/xdvik/ac/xdvik.ac])
@end example

@noindent and specifies the dependency on the @code{kpathsea},
@code{freetype}, and @code{X11} libraries.  The @code{M4} comment (following
@code{dnl}) signals the subsidiary @file{squeeze/configure.ac}.  This is
needed because the main executable @file{xdvi-bin} (to be installed as,
e.g., @file{xdvi-xaw}) is for the @code{host} system whereas the auxiliary
program @file{squeeze/squeeze} has to run on the @code{build} system and in
a cross compilation they differ.  The additional fragment @code{ac/xdvik.ac}
is also included by @file{configure.ac} and supplies the configure option
@code{--with-xdvi-x-toolkit} also seen at the top-level.

@subsubsection The subdirectory @file{utils/asymptote}

This subdirectory contains the sources for @file{asy} and @file{xasy} but
due to its complexity and prerequisites (e.g., @file{libGL}) it is not part
the @TL{} build system.  These programs must be built and installed
independently, but are contained in the @TL{} DVD together with their
support files.


@node Extending
@subsection Adding New Modules

@subsubsection Adding a New Program Module

A @TeX{} specific program module in a subdirectory @file{texk/@var{prog}} may use
the @TeX{} specific libraries and is included by adding its name @file{@var{prog}}
to the @code{M4} list @code{kpse_texk_pkgs} defined in
@file{m4/kpse-pkgs.m4}.  A generic program module in a subdirectory
@file{utils/@var{prog}} must not use the @TeX{} specific libraries and is included
by adding its name @file{@var{prog}} to the @code{M4} list @code{kpse_utils_pkgs}
in @file{m4/kpse-pkgs.m4}.  Apart from the program sources and build system
(@file{configure.ac} and @file{Makefile.am}) the subdirectory
@file{texk/@var{prog}} or @file{utils/@var{prog}} must provide a fragment
@file{ac/withenable.ac} that contains the @code{M4} macro
@code{KPSE_ENABLE_PROG} defined in @file{m4/kpse-setup.m4} with @code{@var{prog}}
as mandatory first argument and three optional arguments: a list of required
libraries from the @TL{} tree, a list of options (@code{disable} if this
module is not to be built without the configure option @code{--enable-@var{prog}},
@code{native} if cross compilation is not possible, @code{x} if the program
requires X11 libraries), and a comment added to the help text for the
configure option @code{--enable-@var{prog}} or @code{--disable-@var{prog}}.

If the module requires specific configure options to be seen at the
top-level, they should be defined in an additional fragment
@file{ac/@var{prog}.ac} included from @file{ac/withenable.ac} and
@file{configure.ac}.

@subsubsection Adding a New Generic Library Module

A generic library module in a subdirectory @file{libs/@var{lib}} must not depend
on @TeX{} specific libraries and is included by adding its name @file{@var{lib}}
to the @code{M4} list @code{kpse_libs_pkgs} in @file{m4/kpse-pkgs.m4}
(before other libraries from the @TL{} tree it depends on).  As for program
modules the subdirectory @file{libs/@var{lib}} must contain the sources and build
system for the library (and any installable support programs) and a fragment
@file{ac/withenable.ac} that contains the @code{M4} macro
@code{KPSE_WITH_LIB} defined in @file{m4/kpse-setup.m4} with @code{@var{lib}} as
mandatory first argument and two optional arguments: a list of required
libraries from the @TL{} tree, and a list of options (currently only
@code{tree} if this library can not be replaced by a system version).

If a system version can be used, a second fragment @file{ac/@var{lib}.ac}
containing the @code{M4} macro @code{KPSE_TRY_LIB} (or
@code{KPSE_TRY_LIBXX}) with @code{@var{lib}} as mandatory first argument and
two additional arguments for the Autoconf macro @code{AC_LANG_PROGRAM} used
to compile and link a small C (or C++) program as sanity check for using the
system library.

In addition a file @file{m4/kpse-@var{lib}-flags} (at the top-level) must define
the @code{M4} macro @code{KPSE_@var{LIB}_FLAGS} (all uppercase) setting up the @code{make}
variables @code{@var{LIB}_INCLUDES}, @code{@var{LIB}_LIBS}, @code{@var{LIB}_DEPEND}, and
@code{@var{LIB}_RULE} with the values required for @code{CPPFLAGS}, @code{LDADD},
dependencies, and a (multiline) make rule to rebuild the library when
necessary, all that for the library from the @TL{} tree or perhaps for a
system version.

If a system library is allowed @code{KPSE_@var{LIB}_FLAGS} also provides the
configure option @code{--with-system-@var{lib}} and uses the additional @code{M4}
macro @code{KPSE_@var{LIB}_SYSTEM_FLAGS} to generate the @code{make} variables for
a system library.  Furthermore the definition of the @code{M4} macro @code{KPSE_ALL_SYSTEM_FLAGS} in
@file{m4/kpse-pkgs.m4} must be extended by the line @* @ @ @
@code{AC_REQUIRE([KPSE_@var{LIB}_SYSTEM_FLAGS])}

@subsubsection Adding a New @TeX{} Specific Library Module

A @TeX{} specific library module in a subdirectory @file{texk/@var{lib}} may
depend on other @TeX{} specific libraries but must not depend on any generic
library from the @TL{} tree.  It is included as is a generic library module
with these modifications:

@itemize @bullet
@item
The library name @code{@var{lib}} is added to the @code{M4} list
@code{kpse_texlibs_pkgs} also in @file{m4/kpse-pkgs.m4}.

@item
The fragment @code{ac/withenable.ac} must use @code{KPSE_WITH_TEXLIB}.

@end itemize

@subsection Using Libraries from the @TL{} Tree

The @TL{} build system provides Autoconf macros for all libraries in the
@TL{} tree.  A program requiring additional libraries must use standard
Autoconf and Automake features (such as @code{AC_ARG_WITH} for search paths,
@code{AC_CHECK_LIB} and @code{AC_CHECK_FUNCS} for library functions, or
@code{AC_CHECK_HEADERS} for header files).

@subsubsection @file{configure.ac}

In order to use, e.g., @file{libpng} (either an installed version or from
the @TL{} tree) @file{configure.ac} must use @* @ @ @ @code{KPSE_ZLIB_FLAGS}
@* @ @ @ @code{KPSE_LIBPNG_FLAGS} @* to define the Make variables
@code{LIBPNG_DEPEND}, @code{LIBPNG_INCLUDES}, @code{LIBPNG_LIBS}, and
@code{LIBPNG_RULE} (and analogous @code{ZLIB_*} variables).  To examine some
@file{libpng} features, @file{configure.ac} must use @* @ @ @
@code{KPSE_ADD_FLAGS([@file{zlib}])} @* followed by tests for @file{zlib}
features (if any) and @* @ @ @ @code{KPSE_ADD_FLAGS([@file{libpng}])} @*
followed by tests for @file{libpng} features.  These macros temporarily add
appropriate values to @code{CPPFLAGS} and @code{LIBS}.  The tests must be
terminated by @* @ @ @ @code{KPSE_RESTORE_FLAGS} @* to restore
@code{CPPFLAGS} and @code{LIBS} to their former values.

@subsubsection @file{Makefile.am}

In order to use, e.g., @file{libpng} (and @file{zlib}) @file{Makefile.am}
must add @* @ @ @ @code{$@{LIBPNG_INCLUDES@}} @code{$@{ZLIB_INCLUDES@}} @*
to @code{AM_CPPFLAGS} (or target specific @code{@var{target}_CPPFLAGS}) and
@* @ @ @ @code{$@{LIBPNG_LIBS@}} @code{$@{ZLIB_LIBS@}} @* to @code{LDADD} or
@code{@var{target}_LDADD}, and should add @* @ @ @ @code{$@{LIBPNG_DEPEND@}}
@code{$@{ZLIB_DEPEND@}} @* to @code{@var{target}_DEPENDENCIES} such that
rebuilding @file{zlib} and/or @file{libpng} causes the target to be rebuilt. 
Finally the two lines @* @ @ @ @code{@@ZLIB_RULE@@} @* @ @ @
@code{@@LIBPNG_RULE@@} @* create the rules required to (re-)build
@file{zlib} and @file{libpng} when necessary.

@node Configure Options
@section List of all Configure Options

Corresponding to the large number of program and library modules there are
plenty of configure options, most of which are described here.  The command
@* @ @ @ @command{configure --help} @* at the top-level gives an exhaustive
list of all global options and a few important module specific ones,
whereas, e.g., @* @ @ @ @command{texk/lcdf-typetools/configure --help} @*
also displays the @code{lcdf-typetools} specific options not shown at the
top-level.  The help text also mentions several influential environment
variables, but for @TL{} it is better to specify them as assigments on the
command line.

The @file{./Build} script used to make the binaries shipped with @TL{}
invokes the top-level @command{configure} with a few additional options. 
Any defaults discussed below are those for the base @command{configure}
script; invoking @command{configure} via @file{./Build} may yield different
results.

Defaults for most options are set at the top-level and propagated explicitly
to all subdirectories.  Options specified on the command line are checked
for consistency but are never modified.

@menu
* Global Options::              Global Configure Options.
* Program Specific Options::    Configure Options for Program Modules.
* Library Specific Options::    Configure Options for Library Modules.
* Variable Assignments::        Interesting and/or Important Variables.
@end menu

@node Global Options
@subsection Global Configure Options

@subsubsection @code{--disable-native-texlive-build}

If enabled (the default), build for a @TL{} binary distribution as shipped
by the user groups; this requires GNU @command{make} and implies
@code{--enable-multiplatform} and @code{--enable-cxx-runtime-hack} unless
they are explicitly disabled and enforces @code{--disable-shared}.

If building @TL{} for a GNU/Linux or other distribution, this would be
disabled and system versions of most libraries would be used (see below).
This may require GNU @command{make}, but will also try without it.

A related option @code{--enable-texlive-build} is automatically passed to
all subdirectories (and can not be disabled).  Subdirectories that could
also be built independently from the @TL{} tree (such as @file{utils/xindy}
or @file{texk/dvipng}) can use this option, e.g., to choose @TL{} specific
installation directories.

@subsubsection @code{--prefix}, @code{--exec-prefix}, @code{--bindir}, @dots{}

These options specify various installation directories as usual, all of them
still prefixed by the value of an assignment for @code{DESTDIR} on the
@code{make} command line (@pxref{Staged Installs, , Installation in a
temporary location, automake, GNU Automake}).

@subsubsection @code{--enable-multiplatform}

If enabled, install executables and libraries in platform dependent
subdirectories of @file{EPREFIX/bin} and @file{EPREFIX/lib} (unless
@code{--bindir=@var{dir}} or @code{--libdir=@var{dir}} is specified), where
@code{EPREFIX} is the value given or implied for @code{exec_prefix}.  The
values for @code{bindir} and @code{libdir} are automatically propagated
to all subdirectories.

@subsubsection @code{--enable-cxx-runtime-hack}

If enabled and when using @code{g++}, try to statically link with
@code{libstdc++}, somewhat improving portability.

@subsubsection @code{--enable-libtool-hack}

If enabled (at present the default for all platforms), prevents
@code{libtool} from linking explicitly with @code{dependency_libs}.

@subsubsection @code{--enable-shared}

Build shared versions of the @TeX{} specific (@code{kpathsea} and
@code{ptexenc}) libraries; this is not allowed for a native @TL{} build.

@subsubsection @code{--disable-largefile}

Omit large file support (LFS), needed on most 32-bit Unix systems for files
with 2GB or more.  The size of @code{DVI} and @code{GF} files must always be
@math{<2}GB.  With LFS there should be no limit on the size of @code{PDF}
files created by @file{pdftex} or @code{PS} files created by @file{dvips}. 
The size of @code{PDF} images included by @file{pdftex} must, however, be
@math{<4}GB when using @file{xpdf} and @math{<2}GB when using older versions
of @file{poppler} (even on 64-bit systems with LFS), whereas @file{poppler}
Version@tie{}0.23 and later imposes no such limit.

@subsubsection @code{--without-x}

Disable all programs using the X Window System.

@subsubsection @code{--enable-compiler-warnings=[no|min|yes|max|all]}

Enable various degrees of compiler warnings for (Objective) C and C++.  The
default is @code{yes} in maintainer-mode and @code{min} otherwise.  This
option defines @code{WARNING_[OBJ]C[XX]FLAGS} but these flags are not used in all
library and program modules.  Using them should help to resolve portability
problems.

At the moment these warning flags are only defined for the GNU
compilers but flags for other compilers could be added when needed.

@subsubsection @code{--disable-missing}

Immediately terminate the build process if a requested program or feature
must be disabled, e.g., due to missing libraries.

@subsubsection @code{--enable-silent-rules}

Enable the use of less verbose build rules.  When using GNU @command{make} or
another @command{make} implementation that supports nested variable expansions
you can always specify @code{V=1} on the make command line to get more
respectively @code{V=0} to get less verbosity.

@subsubsection @code{--without-ln-s}

Required to build without working @code{ln -s} for a Unix-like system.  But
note that @code{make install} will not create anything useful and might even
fail.

@subsubsection @code{--enable-maintainer-mode}

Enable @file{make} rules and dependencies not useful (and sometimes
confusing) to the casual user.  This requires current versions of the GNU
build tools.

@node Program Specific Options
@subsection Configure Options for Program Modules

@subsubsection @code{--enable-@var{prog}}, @code{--disable-@var{prog}}

Do or do not build and install the program(s) of the module @code{@var{prog}}.

@subsubsection @code{--disable-all-pkgs}

Do not build any program modules, except those explicitly enabled.  Without
this option, all modules are built except those that are explicitly disabled
or specify @code{disable} in their @file{ac/withenable.ac} fragment.

@subsubsection Configure options for @file{texk/web2c}

@noindent @code{--with-banner-add=@var{str}} @* Add @code{@var{str}} to the
default version string (@code{TeX Live @var{year}} or @code{Web2C
@var{year}}) appended to banner lines.  This is ignored for a native @TL{}
build, but distro builds should specify, e.g., @code{/@var{SomeDistro}}.

@noindent @code{--with-editor=@var{cmd}} @* Specify the command
@code{@var{cmd}} to invoke from the @code{e} option of @TeX{}-like engines,
replacing the default @code{vi +%d '%s'} for Unix or @code{texworks
--position=%d "%s"} for Windows.

@noindent @code{--enable-auto-core} @* This option causes @TeX{} & METAFONT
to produce a core dump when a particular hacky filename is encountered.

@noindent @code{--disable-dump-share} @* Make the @code{fmt}/@code{base}
dump files architecture dependent (somewhat faster on little-endian
architectures).

@noindent @code{--disable-ipc} @* Disable @TeX{}'s @code{--ipc} option.

@noindent @code{--disable-tex}, @code{--enable-etex}, @dots{} @* Do not or
do build the various @TeX{}, METAFONT, and MetaPost engines (defaults are
defined in the fragment @file{texk/web2c/ac/web2c.ac}).

@noindent @code{--enable-tex-synctex}, @code{--disable-etex-synctex},
@dots{} @* Build the various @TeX{}-like engines with or without
@code{SyncTeX} support (ignored for a native @TL{} build, defaults are
again defined in @file{texk/web2c/ac/web2c.ac}).

@noindent @code{--with-mf-x-toolkit} @* Use the X toolkit (@file{libXt}) for
METAFONT (default is yes).

@noindent @code{--enable-*win} @* Include various types of other window
support for METAFONT.

@noindent @code{--disable-mf-nowin} @* Do not build a separate
non-graphically-capable METAFONT.

@noindent @code{--disable-web-progs} @* Do not build the WEB programs
@file{bibtex}, @dots{}, @file{weave}, e.g., if you just want to (re)build
some engines.

@noindent @code{--disable-omfonts} @* Build the WEB versions of the
Omega font utilities @file{ofm2opl}, @file{opl2ofm}, @file{ovf2ovp}, and
@code{ovp2ovf} instead of the C version @file{omfonts}. The WEB and C versions
should be roughly equivalent.

@subsubsection Configure options for @file{texk/bibtex-x}

The former modules @code{bibtex8} and @code{bibtexu} have been merged into
@code{bibtex-x} (extended BibTeX).

@noindent @code{--disable-bibtex8} @* Do not build the @file{bibtex8} program.

@noindent @code{--disable-bibtexu} @* Do not build the @file{bibtexu} program
(building @file{bibtexu} requires @code{ICU} libraries).

@subsubsection Configure options for @file{texk/dvipdfm-x}

The former modules @code{dvipdfmx} and @code{xdvipdfmx} have been merged into
@code{dvipdfm-x}.

@noindent @code{--disable-dvipdfmx} @* Do not build the @file{dvipdfmx} program.

@noindent @code{--disable-xdvipdfmx} @* Do not build the @file{xdvipdfmx}
program (building @file{xdvipdfmx} requires the @code{freetype} library).

@subsubsection Configure options for @file{texk/dvisvgm}

@noindent @code{--with-system-libgs} @* Build @file{dvisvgm} using installed
Ghostscript (@code{gs}) headers and library (not allowed for a native @TL{}
build).  The default is to load the @code{gs} library at runtime if
possible, or otherwise disable support for PostScript specials.

@noindent @code{--with-libgs-includes=@var{dir}}, @code{--with-libgs-libdir=@var{dir}}
@* Specify non standard locations of the Ghostscript headers and library.

@subsubsection Configure options for @file{texk/xdvik}

@noindent @code{--with-gs=@var{path}} @* Hardwire the location of Ghostscript
(@file{gs}).

@noindent @code{--with-xdvi-x-toolkit=@var{kit}} @* Use toolkit @code{@var{kit}}
(@code{motif}/@/@code{xaw}/@/@code{xaw3d}/@/@code{neXtaw}) for @file{xdvi}. 
The default is @code{motif} if available, else @code{xaw}.

@subsubsection Configure options for @file{utils/xindy}

@noindent @code{--enable-xindy-rules} @* Build and install xindy rules
(default: yes, except for a native @TL{} build).

@noindent @code{--enable-xindy-docs} @* Build and install xindy
documentation (default: yes, except for a native @TL{} build).

@noindent @code{--with-clisp-runtime=@var{path}} @* Specifies the full path
of the @code{CLISP} runtime (@file{lisp.run} or @file{lisp.exe}) to be
installed.  When specified as @code{default} (the default for a native TeX
Live build) the path is determined by the @code{CLISP} executable; the value
@code{system} (not allowed for a native @TL{} build, but the default for
a non-native one) indicates that @file{xindy} will use the installed version
of @file{clisp} (that must be identical to the one used to build @file{xindy}).

@noindent @code{--with-recode} @* Use @file{recode} instead of @file{iconv}
to build the xindy rules and documentation, required for some systems where
@file{iconv} is missing or broken.


@node Library Specific Options
@subsection Configure Options for Library Modules

@subsubsection @code{--with-system-@var{lib}}

Use an installed (system) version of the library @code{@var{lib}}; this
option exists for most libraries, but is not allowed for a native @TL{}
build.  Using a system version implies to also use system versions of all
libraries (if any) this library depends on.

For many libraries there are in addition
@code{--with-@var{lib}-includes=@var{dir}} and
@code{--with-@var{lib}-libdir=@var{dir}} to indicate non standard search
locations, others use @file{pkg-config} or similar to determine the required
flags.

The top-level @file{configure} script performs a consistency check for all
required system libraries and bails out if some of these tests fail.

@subsubsection Configure Options for @code{kpathsea}

@noindent @code{--enable-@var{cmd}-default},
@code{--disable-@var{cmd}-default} @* Determine the compile time default
whether or not to run @var{cmd}=@command{mktexmf}, @command{mktexpk},
@command{mktextfm}, @command{mkocp}, @command{mkofm}, @command{mktexfmt}, or
@command{mktextex} to generate a missing MF source, PK font, TFM file, OCP
file, OFM file, format file, or @TeX{} source respectively.

@subsubsection Configure Options for @code{fontconfig}

Building @code{XeTeX} on non-Mac systems requires @code{fontconfig} headers
and library.

@noindent @code{--with-fontconfig-includes=@var{dir}},
@code{--with-fontconfig-libdir=@var{dir}} @* If one or both of these options are
given, the required flags are derived from them; otherwise, they are
determined via @file{pkg-config} (if present).

@subsubsection Configure Options for system @file{poppler}

Building @code{LuaTeX} and @code{XeTeX} requires @code{poppler} either from
the @TL{} tree or system headers and library; @code{pdfTeX} requires either
@code{xpdf} from the @TL{} tree or system @code{poppler} headers and
library.

@noindent @code{--with-system-poppler} @* Use a system version (0.18 or
better) of @code{poppler} for @code{LuaTeX} and @code{XeTeX} (and
@file{pkg-config} to obtain the required flags).

@noindent @code{--with-system-xpdf} @* Use a system version (0.12 or better)
of @code{poppler} (and @file{pkg-config}) for @code{pdfTeX} instead of
@code{xpdf} from the @TL{} tree.

REFER to @code{--disable-largefile}

@node Variable Assignments
@subsection Interesting and/or Important Variables

The values for these variables can come either from the environment or from
@file{configure} arguments of the form @code{VAR=value}.

@subsubsection @code{CC}, @code{CXX}, @code{CPPFLAGS}, @dots{}

As usual, these variables specify the name (or full path) of compilers,
preprocessor flags, and similar.

@subsubsection @code{FT2_CONFIG}, @code{ICU_CONFIG}, @code{PKG_CONFIG}

These specify the name (or path) for the @file{freetype-config},
@file{icu-config}, and @file{pkg-config} commands used to determine the
flags required for system versions of @file{libfreetype}, the @code{ICU}
libraries, or many other libraries.

@subsubsection @code{CLISP}

Name (or path) of the @file{clisp} executable, used to build @code{xindy}.

@subsubsection @code{PERL}, @code{LATEX}, @code{PDFLATEX}

Name (or path) for the @file{perl}, @file{latex}, and @file{pdflatex}
commands used, e.g., to build the @code{xindy} documentation

@subsubsection @code{TL_PLATFORM}

The utility program @file{biber} consists of many components bundled by the
@code{Par::Packer} mechanism of @file{perl}.  Therefore they are not built
as part of @TL{} but by the @code{biber} maintainers and third-party
builders.

In order that @code{make install} creates all executables in @file{bindir},
the @code{biber} module contains pre-made binaries for the platforms for
which they are available.  @TL{} merely checks if an executable is present
for the current platform, and if so, installs it.

The complication is hidden in the phrase "current platform".  @TL{} has its
own ideas about platform names, and the mapping from the canonical system
name determined by @file{config.guess} or @file{config.sub} to the @TL{}
platform name is not trivial.  A value given for @code{TL_PLATFORM} is used
as @TL{} platform name.  Otherwise, we use copies of the standard
@code{perl} modules @code{TeXLive/TLUtils.pm} and
@code{TeXLive/TLConfig.pm}, to avoid duplicating the platform-detection
logic.

@subsubsection @code{KPSEWHICH}

Name (or path) of an installed @file{kpsewhich} binary, used by @code{make
check} to determine the location of, e.g., @file{cmbx10.tfm}.

@subsubsection @code{MAKE}, @code{SED}, @dots{}

Name (or path) of GNU @command{make}, GNU @command{sed}, and similar; used
at the top-level and propagated to all subdirectories.


@node Cross Compilation
@section Cross Compilation

In a cross compilation a @code{build} system is used to create binaries to
be executed on a @code{host} system with different hardware and/or operating
system.

In simple cases the build system can execute binaries for the host system. 
This typically occurs for bi-arch systems where, e.g., @code{i386-linux}
binaries can run on @code{x86_64-linux} systems and @code{win32} binaries
can run on @code{win64} systems.  Although sometimes called "native cross",
this is technically no cross compilation.  In most such cases it suffices to
specify suitable compiler flags.  It might be useful to add the configure
option @code{--build=@var{host}} to get the correct canonical host name, but
note that this should not be @code{--host=@var{host}} (@pxref{Hosts and
Cross-Compilation, , , autoconf, Autoconf})!

@menu
* Configuring::                 Configuring for Cross Compilation.
* Problems::                    Cross Compilation Problems.
@end menu

@node Configuring
@subsection Configuring for Cross Compilation

In a genuine cross compilation binaries for the host system can not execute
on the build system and it is necessary to specify the configure options
@code{--host=@var{host}} and @code{--build=@var{build}} with two different
values.  Building binaries requires suitable "cross" tools, e.g., compiler,
linker, and archiver, and perhaps a "cross" version of @command{pkg-config}
and similar to locate host system libraries.  Autoconf expects that these
cross tools are given by their usual variables or found under their usual
name prefixed with @code{@var{host}-}.  Here a list of such tools and
corresponding variables:

@example
@file{ar}                @code{AR}
@file{freetype-config}   @code{FT2_CONFIG}
@file{g++}               @code{CXX}
@file{gcc}               @code{CC}
@file{icu-config}        @code{ICU_CONFIG}
@file{objdump}           @code{OBJDUMP}
@file{pkg-config}        @code{PKG_CONFIG}
@file{ranlib}            @code{RANLIB}
@file{strip}             @code{STRIP}
@end example

@noindent In order to, e.g., build @code{mingw32} binaries on
@code{x86_64-linux} with a cross compiler found as
@file{i386-pc-mingw32-gcc} one would specify @* @ @ @
@code{--host=i386-pc-mingw32 --build=x86_64-linux-gnu} @* or perhaps @* @ @
@ @code{--host=mingw32 --build=x86_64-linux CC=i386-pc-mingw32-gcc} @* but
this might require to add @code{CXX} and others.

Configure arguments such as @code{CFLAGS=@dots{}} refer to the cross compiler. 
If necessary, you can specify compilers and flags for the few auxiliary C
and C++ programs required for the build process as configure arguments

@example
@code{BUILDCC=@dots{}}
@code{BUILDCPPFLAGS=@dots{}}
@code{BUILDCFLAGS=@dots{}}
@code{BUILDCXX=@dots{}}
@code{BUILDCXXFLAGS=@dots{}}
@code{BUILDLDFLAGS=@dots{}}
@end example

@node Problems
@subsection Cross Compilation Problems

The fact that binaries for the host system can not be executed on the build
system causes some problems.

One problem is, that configure tests using @code{AC_RUN_IFELSE} can compile
and link the test program but can not execute it.  Such tests should be
avoided if possible and otherwise must supply a pessimistic test result.

An other problem arises if the build process must execute some (auxiliary or
installable) programs.  Auxiliary programs can be placed into a subdirectory
that is configured natively as is done for @file{texk/dvipsk/squeeze},
@file{texk/web2c/web2c}, and @file{texk/xdvik/squeeze}.  The module
@file{libs/freetype} uses the value of @code{CC_BUILD},
@file{@var{build}-gcc}, @file{gcc}, or @file{cc} as compiler for the
auxiliary program.

The situation for installable programs needed by the build process is
somewhat different.  A quite expensive possibility, chosen for the
@code{ICU} libraries in module @file{libs/icu}, is to first compile natively
for the build system and in a second step to use these (uninstalled)
programs during the cross compilation.  This would also be possible for the
tools such as @file{tangle} used in the module @file{texk/web2c} to build
the WEB programs, but that would require to first build a native
@code{kpathsea} library.  To avoid this complication, cross compilation of
the WEB or CWEB programs in this module requires sufficiently recent
installed versions of @file{tangle}, @file{ctangle}, @file{otangle}, and
@file{tie}.

Building @code{xindy} requires to run the host system @file{clisp} binary,
thus cross compilation is not possible.

@node Coding Rules
@section Coding Rules

Ideally, building all of @TL{} with @code{--enable-compiler-warnings=max}
should produce no (GCC) compiler warnings at all.  In spite of
considerable efforts into that direction we are still far from that goal and
there are reasons that we may never fully reach it.  Below are some rules
about declarations of functions or variables and the use of @code{const}. 
These rules should be applied to all parts of the @TL{} tree, except some of
those maintained independently.

@subsection Declarations

@subsubsection ANSI C function prototypes and definitions

The @TL{} build system no longer supports pre-ANSI C compilers. 
Thus all function prototypes and definitions must conform to the
ANSI C standard (including @code{void} in the declaration of C
functions with no parameters).  On the other hand @TL{} is built for many
different systems, some of them not supporting the C99 standard.  Therefore
using C99 features should be avoided if that can easily be done.  In
particular C code must not contain declarations after statements or C++ type
comments.

If some C99 (or later) constructs have to be used, the module should verify
that they are available and otherwise provide an alternative.  The module
@file{texk/chktex} uses, e.g., the C99 function @code{stpcpy()} that may or
may not be available on a particular system, uses
@code{AC_CHECK_DECLS([stpcpy])} in @file{configure.ac} to test this, and
provides the perhaps slightly less efficient alternative @* @ @ @ @code{#if
!(defined HAVE_DECL_STPCPY && HAVE_DECL_STPCPY)} @* @ @ @ @code{static
inline char * stpcpy(char *dest, const char *src)} @* @ @ @ @code{@{} @* @ @
@ @code{@ @ @ return strcpy(dest, src) + strlen(src);} @* @ @ @ @code{@}} @* @ @
@ @code{#endif} @* in the file @file{Utility.h}.

@subsubsection Static Functions

Functions used in only one file should be declared @code{static}; they
require no prototype except as forward declaration.

@subsubsection Extern Functions

Functions not declared @code{static}, usually because they are used in
several files, require an (@code{extern}) prototype in exactly one header
which is included in the file defining the function and in all files using
that function --- this is the only way to guarantee consistency between
definition and use of functions.  There must be no @code{extern}
declarations sprinkled throughout the C code (with or without comment where
that function is defined).

@subsubsection Variables

The declaration of global variables must follow analogous rules, they are
either declared @code{static} if used in only one files or declared
@code{extern} in exactly one header and instantiated in exactly one file.

@subsection Const

@subsubsection Function Parameters

Ideally, a function parameter not modified by the function should be
declared as @code{const}.  This is important in particular for strings
(@code{char*}) because the actual arguments are often string literals.  It
is perfectly legitimate and safe to use a type @code{char*} value for a type
@code{const char*} variable (in an assignment, as initializer, as function
argument, or as return value).  It is equally safe to use a type
@code{char**} value for a type @code{const char*const*} variable, but not
for a type @code{const char**} variable since that might cause modification
of a quantity supposed to be constant.  Getting all @code{const} qualifiers
right is often quite involved but can be done in most cases.  There are,
however, a few notable exceptions: the X11 headers are full of declarations
that ought to use @code{const} but do not and the same is true to some
extent for @file{libfreetype} (but not anymore for @code{zlib}).

@subsubsection What Must be Avoided

The GCC compiler warnings "assignment discards qualifiers@dots{}" and
analogous warnings for "initialization", "passing arg", or "return" must be
avoided under all circumstances, except when caused by X11 headers/macros or
third party code.

@subsubsection What Should be Avoided

A type cast, e.g., from @code{const char*} to @code{char*} does not solve
any problems; depending on warning options, it may only hide them. 
Therefore such casts should be avoided whenever possible and otherwise must
be carefully analyzed to make sure that they can not cause the modification
of quantities supposed to be constant.