Build Instructions
------------------

* Requirements
  ------------

  - A POSIX-compliant C development environment
  - GNU make version 3.81 or later
  - skalibs version 2.8.0.1 at least commit e99801ab4bdd096b5e2e3e4619f1a8317a8aedf8 
  or later: http://skarnet.org/software/skalibs/
  - If cross-compiling: the sysdeps for your target architecture
    (see the "Cross-compilation" section below)

 This software will install on any operating system that implements
POSIX.1-2008, available at:
  http://pubs.opengroup.org/onlinepubs/9699919799/


* Standard usage
  --------------

  ./configure && make && sudo make install

 will work for most users.
 It will install the static libraries in /usr/lib/oblibs, the shared
libraries in /lib.

 Please note that static libraries in /usr/lib/oblibs *will not*
be found by a default linker invocation: you need -L/usr/lib/oblibs.
Other obarun.org software automatically handles that case if the
default configuration is used, but if you change the configuration,
remember to use the appropriate --with-lib configure option.

 You can strip the libraries of their extra symbols via "make strip"
before the "make install" phase. It will shave a few bytes off them.


* Customization
  -------------

 You can customize the installation process via flags given to configure.
 See ./configure --help for a list of all available configure options.


* Environment variables
  ---------------------

 Controlling a build process via environment variables is a big and
dangerous hammer. You should try and pass flags to configure instead;
nevertheless, a few standard environment variables are recognized.

 If the CC environment variable is set, its value will override compiler
detection by configure. The --host=HOST option will still add a HOST-
prefix to the value of CC.

 The values of CFLAGS, CPPFLAGS and LDFLAGS will be appended to the
default flags set by configure. To override those defaults instead
of appending to them, use the CPPFLAGS, CFLAGS and LDFLAGS
_make variables_ instead of environment variables.


* Make variables
  --------------

 You can invoke make with a few variables for more configuration.

 CC, CFLAGS, CPPFLAGS, LDFLAGS, LDLIBS, AR, RANLIB, STRIP, INSTALL and
CROSS_COMPILE can all be overridden on the make command line. This is
an even bigger hammer than running ./configure with environment
variables, so it is advised to only do this when it is the only way of
obtaining the behaviour you want.
 
 DESTDIR can be given on the "make install" command line in order to
install to a staging directory.


* Shared libraries
  ----------------

 Software from obarun.org is small enough that shared libraries are
generally not worth using. Static linking is simpler and incurs less
runtime overhead and less points of failure: but since oblibs only
provides libraries, both versions are built by default.
 Nevertheless, you can:
  * avoid building shared libraries: --disable-shared
  * avoid building static libraries: --disable-static

 If you are using a GNU/Linux system, be aware that the GNU libc
behaves badly with static linking and produces huge executables,
so if you plan on making static executables, you should consider
using another libc, which you also need to use when compiling
oblibs. musl is recommended: http://musl-libc.org/

* Cross-compilation
  -----------------

 skarnet.org packages centralize all the difficulty of
cross-compilation in one place: skalibs. Once you have
cross-compiled skalibs, the rest is easy.

 * Use the --host=HOST option to configure, HOST being the triplet
for your target.
 * Make sure your cross-toolchain binaries (i.e. prefixed with HOST-)
are accessible via your PATH environment variable.
 * Make sure to use the correct version of skalibs for your target,
and the correct sysdeps directory, making use of the
--with-include, --with-lib, --with-dynlib and --with-sysdeps
options as necessary.

* The slashpackage convention
  ---------------------------

 The slashpackage convention (http://cr.yp.to/slashpackage.html)
is a package installation scheme that provides a few guarantees
over other conventions such as the FHS, for instance fixed
absolute pathnames. obarun.org packages support it: use the
--enable-slashpackage option to configure, or
--enable-slashpackage=DIR for a prefixed DIR/package tree.
This option will activate slashpackage support during the build
and set slashpackage-compatible installation directories. If
$version is the current oblibs version number:

 --bindir will be set to /package/prog/oblibs-$version/command
 --includedir will be set to /package/prog/oblibs-$version/include
 --libdir will be set to /package/prog/oblibs-$version/library
 --dynlibdir will be set to /package/prog/oblibs-$version/library.so


 Note that --datadir will be unchanged, because the data exported
by oblibs, i.e. the leap second table, is system-wide. You should
manually specify --datadir=... if you want to deviate from the default.

 --prefix is pretty much ignored when you use --enable-slashpackage:
it will only impact --datadir. You should probably not use both
--enable-slashpackage and --prefix.

 When using slashpackage, two additional Makefile targets are
available after "make install":
 - "make -L update" changes the default version of the software to the
freshly installed one. (This is useful when you have several installed
versions of the same software, which slashpackage supports.)
 - "make -L global-links" adds links from DIR/command and DIR/library.so
to the default version of the binaries and shared libraries.
 The "-L" option to make is necessary because targets are symbolic links,
and the default make behaviour is to check the pointed file's timestamp
and not the symlink's timestamp.


* Out-of-tree builds
  ------------------

 obarun.org packages do not support out-of-tree builds. They
are small, so it does not cost much to duplicate the entire
source tree if parallel builds are needed.
