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+Build Instructions
+------------------
+
+* Requirements
+  ------------
+
+  - A POSIX-compliant C development environment
+  - GNU make version 3.81 or later
+  - skalibs version 2.10.0.0 or later: https://skarnet.org/software/skalibs/
+  - s6-dns version 2.3.3.0 or later: https://skarnet.org/software/s6-dns/
+
+ This software will run 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 binaries in /bin.
+
+ You can strip the binaries and 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 paths 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 flags
+auto-detected by configure. To entirely override the flags set by
+configure instead, use make 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 skarnet.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: so by default, shared
+libraries are not built and binaries are linked against the static
+versions of the skarnet.org libraries. Nevertheless, you can:
+  * build shared libraries: --enable-shared
+  * link binaries against shared libraries: --disable-allstatic
+
+
+* Static binaries
+  ---------------
+
+ By default, binaries are linked against static versions of all the
+libraries they depend on, except for the libc. You can enforce
+linking against the static libc with --enable-static-libc.
+
+ Be aware that the GNU libc behaves badly with static linking and
+produces huge executables, which is why it is not the default.
+Other libcs are better suited to static linking, for instance
+musl: 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. skarnet.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 $package_home is the home of the package, defined as
+DIR/package/$category/$package-$version with the variables
+read from the package/info file, then:
+
+  --dynlibdir is set to $package_home/library.so
+  --bindir is set to $package_home/command
+  --sbindir is also set to $package_home/command (slashpackage
+differentiates root-only binaries by their Unix rights, not their
+location in the filesystem)
+  --libexecdir is also set to $package_home/command (slashpackage
+does not need a specific directory for internal binaries)
+  --libdir is set to $package_home/library
+  --includedir is set to $package_home/include
+
+ --prefix is pretty much ignored when you use --enable-slashpackage.
+You should probably not use both --enable-slashpackage and --prefix.
+
+ When using slashpackage, two additional Makefile targets are
+available after "make install":
+ - "make 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 /command and /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.
+
+
+* Absolute pathnames
+  ------------------
+
+ You may want to use fixed absolute pathnames even if you're not
+following the slashpackage convention: for instance, the Nix packaging
+system prefers calling binaries with immutable paths rather than rely on
+PATH resolution. If you are in that case, use the --enable-absolute-paths
+option to configure. This will ensure that programs calling binaries from
+this package will call them with their full installation path (in bindir)
+without relying on a PATH search.
+
+
+* Out-of-tree builds
+  ------------------
+
+ skarnet.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.