After a couple releases, it appears that the minimum version can be
increased without much trouble.
Because meson only requires python 3.7 or greater, most supported
distributions can run a newer meson without having to deal with
additional dependencies or a new python version.
Enabling LTO yields substantial performance gains on both authoritative
and resolver benchmarks.
But since LTO defers many optimization passes to link time, enabling LTO
across the board would cause an increase in compilation time, as passes
that would be run only once would need to be run for each executable.
As a compromise, this commit adds a named-lto build option, that
compiles the individual object files with the -ffat-lto-object option
and then enables LTO only for the named executable. Object files are
reused between lib*.so and the named executable.
The 'plain' optimization level doesn't add any flags and gives the
control to the packager. Similarly, avoid any hardening flags in this
level.
Necessary flags such as `-fno-delete-null-pointer-checks` and
`-fno-strict-aliasing` are still included.
Meson is a modern build system that has seen a rise in adoption and some
version of it is available in almost every platform supported.
Compared to automake, meson has the following advantages:
* Meson provides a significant boost to the build and configuration time
by better exploiting parallelism.
* Meson is subjectively considered to be better in readability.
These merits alone justify experimenting with meson as a way of
improving development time and ergonomics. However, there are some
compromises to ensure the transition goes relatively smooth:
* The system tests currently rely on various files within the source
directory. Changing this requirement is a non-trivial task that can't
be currently justified. Currently the last compiled build directory
writes into the source tree which is in turn used by pytest.
* The minimum version supported has been fixed at 0.61. Increasing this
value will require choosing a baseline of distributions that can
package with meson. On the contrary, there will likely be an attempt
to decrease this value to ensure almost universal support for building
BIND 9 with meson.
The OpenSSL 1.x Engines support has been deprecated in the OpenSSL 3.x
and is going to be removed. Remove the OpenSSL Engine support in favor
of OpenSSL Providers.
BIND needs a collection of standard lock-free data structures,
which we can find in liburcu, along with its RCU safe memory
reclamation machinery. We will use liburcu's QSBR variant instead
of the home-grown isc_qsbr.
The implementation of UDP recvmmsg in libuv 1.35 and 1.36 is
incomplete and could cause assertion failure under certain
circumstances.
Modify the configure and runtime checks to report a fatal error when
trying to compile or run with the affected versions.
By bumping the minimum libuv version to 1.34.0, it allows us to remove
all libuv shims we ever had and makes the code much cleaner. The
up-to-date libuv is available in all distributions supported by BIND
9.19+ either natively or as a backport.
We have had perpetual problem with Sphinx implicitly double-including
files. To avoid that problem all files with name suffix .inc.rst are now
ignored by Sphinx, and writter can conveniently include them without
modifying conf.py for each and every file.
