dinit/BUILD_MESON

Meson build system for Dinit
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<!> Special notes about building Dinit via Meson
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Please keep in mind:
1. Meson build system for Dinit is an experimental way to build Dinit. 
   it might have some bugs. Please report bugs on https://github.com/davmac314/dinit/issues
2. Meson build system for Dinit is "extra" part. The main build system is GNU Make.
   This means that the feature is first tested on Make. There may also be delays
   in adding new Dinit's features to Meson builds.
3. If you found some bugs in Meson builds, Please also test it on GNU make builds.

Buidling Dinit via Meson
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Buidling Dinit is available via two "Build system": meson & make.
This file contains instructions for building Dinit using meson.
Bulding dinit via meson requires "meson" (0.47.0 or later) and a C++11 compiler
(GCC version 4.9 and later, or Clang ~5.0 and later, should be fine).


Short version
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Run "meson setup builddir && meson compile -C builddir". Your system type will
hopefully be detected automatically and appropriate configuration chosen, and Dinit
will be built. Continue reading instructions at "Running the test suite" or skip
straight to "Installation".

If this fails, or if you are cross-compiling, read the "long version" instructions.


Long version
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Meson configures all you need to build Dinit. It detects your OS, detects your
compiler & sets something based on your system information.
By Default no action is required & meson configures everything needed to build Dinit.

Note that the "eg++" or "clang++" package must be installed on OpenBSD
as the default "g++" compiler is too old. Clang is a part of the base system
in recent releases.

In Meson you need to prepare the "build directory". simply just type:

    meson setup builddir/

This command configures "build directory" in builddir/. You can set desired
directory (but we suggest don't use dinit's directory such as build/ & src/ or ...
as "build dir"). If everything goes smoothly this will prepare everything to
build dinit, dinitctl and optionaly the shutdown/reboot/halt utilitys by default.

Everything is ready! you can compile Dinit with

     meson compile -C builddir

This command builds the dinit, dinitctl and optionaly the shutdown/reboot/halt
utilitys by default. Note: on Mesons older than 0.54, you need to use
"ninja -C builddir" instead of "meson compile -C builddir".


Dinit's custom options
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Dinit should generally build with no additional options, all required
options/flags will be added automatically. Custom options can be passed
with command line:

     meson setup -Doption=value builddir/

or users can modify original "meson_options.txt" and set values.

Custom options:
 shutdown-prefix           : Name prefix for "shutdown", "halt" and "reboot"
                             commands (if they are built).
                             This affects both the output, and what command dinit
                             will execute as part of system shutdown. If you want
                             to install Dinit alongside another init system with
                             its own shutdown/halt/reboot commands, set
                             this (for eg. to "dinit-").
                             Available values : everything you want!
                             Default value : (empty)

 build-shutdown            : Whether to build the "shutdown" (and "halt" etc) utilities.
                             These are only useful if dinit is the system init
                             (i.e. the PID 1 process). You probably don't want
                             this unless building for Linux.
                             Available values : enabled, disabled, auto
                             Default value : auto

 dinit-control-socket-path : Default full path to the control socket, for when
                             Dinit runs as system service manager.
                             Available values : anywhere you want!
                             Default value : /run/dinitctl

 unit-tests                : Building Unit tests. see "Running test suite", below.
                             Available values: true, false
                             Default value : false

 igr-tests                 : Building Integration tests. see "Running test suite", below.
                             Available values : true, false
                             Default value : false
 
 fuzzer                    : Building LLVM's Libfuzzer for Dinit. see "Running fuzzer", below.
                             Available values : true, false
                             Default value : false

 use-utmpx                 : Whether to build support for manipulating the
                             utmp/utmpx database via the related POSIX functions.
                             This may be required (along with appropriate service
                             configuration) for utilities like "who" to work
                             correctly (the service configuration items "inittab-id"
                             and "inittab-line" have no effect if this is disabled).
                             If not set to any value, support is enabled for certain
                             systems automatically and disabled for all others.
                             Available values : enabled, disabled, auto
                             Default value : auto

 dinit-sbindir             : Default full path to the dinit executables.
                             For some reasons Dinit dont follow Meson's default
                             sbindir option. see "Why we use another option
                             for sbindir?", below.
                             Available values : anywhere you want!
                             Default value : /sbin
                             
 man-pages                 : Building Dinit's man-pages.
                             Available values : true, false
                             Default value : true
                             
 support-cgroups           : Enable Cgroups supprot.
                             Available values : enabled, disabled, auto
                             Default value : auto

 build-shutdown            : Building shutdown/reboot/halt or not.
                             Available values : enabled, disabled, auto
                             Default value : auto


Running test suite
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Enable "unit-tests" option to run the test suite:

     meson setup -Dunit-tests=true builddir/
     
In Dinit's make build system -fsanitize enabled for unit tests but in meson
it's not enabled. so if you need that use this option in meson setup step:

     meson setup -Db_sanitizes='address,undefined' builddir/

Note: Unlike Dinit's make build system, This flag enables sanitizers for
entire build.

Enable "igr-tests" to run the integration tests:

     meson setup -Digr-tests=true builddir/

(The integration tests are more fragile than the unit tests, but give a
better indication that Dinit will actually work correctly on your system).

Finally compile Dinit with "meson compile -C builddir" and run tests via:

     meson test -C builddir

Then Meson report test status. All test logs available at
"builddir/meson-logs/testlog.txt".


Installation
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You can install dinit via this command:

     meson install -C builddir

If you want to install to an alternate root (eg for packaging purposes),
specify that root via DESTDIR:

     DESTDIR=/tmp/temporary-install-path meson install -C builddir

The dinit executable will be put in "dinit-sbindir" option value (by default /sbin)
(or rather, in $DESTDIR/sbin), which may not be on the path for normal users.
Consider making a symbolic link to /usr/sbin/dinit.


Running fuzzer
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In addition to the standard test suite, there is experimental support for
fuzzing the control protocol handling using LLVM/clang's fuzzer (libFuzzer).
Enable "fuzzer" option to build fuzzer:

    meson setup -Dfuzzer=true builddir

Then changing current directory to Your builddir (eg builddir)/src/tests/cptests/,
create a "corpus" directory and run the fuzzer:

    mkdir corpus
    ./fuzz corpus

This will auto-generate test data as it finds input which triggers new
execution paths. Check libFuzzer documentation for further details.


Why we use another option for sbindir?
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For some reasons, Old Mesons force sbindir will prefixed by Meson's prefix
(eg /usr + sbin) but Dinit project use /sbin by default as sbindir.
in Newer Mesons that fixes this thing but we target Mesons's 0.47.0 as
minimum version. So we use "dinit-sbindir" instead of default "sbindir".


Some notes
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1. Dinit use "custom" buildtype with "'optimization=s', 'debug=false'"
   (-Os, no debug) by default.
2. For building with debug symbols, use "meson setup -Ddebug=true builddir" or
   a buildtype with "debug=true"
3. For enabling LTO, use "meson setup -Db_lto=true builddir" command.


Special note for GCC/Libstdc++
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(Note: the issue discussed here has apparently been resolved in recent GCC versions).

GCC 5.x onwards includes a "dual ABI" in its standard library implementation, aka Libstdc++.
Compiling against the newer (C++11 and later) ABI can be achieved by adding
-D_GLIBCXX_USE_CXX11_ABI=1 to the compiler command line; this uses a non-standard language
extension to differently mangle symbol names in order to link against the new ABI versions.

(Some systems may be configured to build with the new ABI by default, and in that
case you build against the old ABI using -D_GLIBCXX_USE_CXX11_ABI=0).

This is problematic for several reasons. First, it prevents linking against the
new ABI with other compilers that do not understand the language extension
(LLVM i.e. clang++ does so in recent versions, so this is perhaps no longer
much of a problem in practice). Secondly, some aspects of library behaviour are
ABI-dependent but cannot be changed using the ABI macro; in particular, exceptions
thrown as a result of failed I/O operations are, in GCC versions 5.x and 6.x, always
"old ABI" exceptions which cannot be caught by code compiled against the new ABI, and
in GCC version 7.x they are always "new ABI" exceptions which cannot be caught by
code compiled against the old ABI. Since the one library object now supposedly
houses both ABIs, this means that at least one of the two ABIs is always broken.

A blog post describing the dual ABI mechanism can be found here:

    https://developers.redhat.com/blog/2015/02/05/gcc5-and-the-c11-abi/

The bug regarding the issue with catching other-ABI exceptions is here:

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66145

Since Dinit is affected by this bug, the unfortunate possibility exists to break
Dinit by upgrading GCC. If you have libstdc++ corresponding to GCC 5.x or 6.x,
you *must* build with the old ABI, but Dinit will be broken if you upgrade to GCC 7.
If you have libstdc++ from GCC 7, you *must* build with the new ABI. If the wrong
ABI is used, Dinit may still run successfully but any attempt to load a non-existing
service, for example, will cause Dinit to crash.