mkosi: Changes to allow booting with sanitizers in mkosi

- Extra memory because ASAN needs it
- The environment variables to make the sanitizers more useful
- LD_PRELOAD because the ASAN DSO needs to be the first in the list
- The sanitizer library packages
- Disable syscall filters because they interfere with ASAN
- Disable systemd-hwdb-update because it's super slow when systemd-hwdb
  is built with sanitizers
- Take the value for meson's b_sanitize option from the SANITIZERS
  environment variable

docs/HACKING.md

@@ -140,6 +140,11 @@ enabled that are suitable when hacking on systemd (such as internal
 documentation consistency checks). Those are not useful when compiling for
 distribution and can be disabled by setting `-Dmode=release`.
 
+## Sanitizers in mkosi
+
+See [Testing systemd using sanitizers](TESTING_WITH_SANITIZERS.md) for more information
+on how to build with sanitizers enabled in mkosi.
+
 ## Fuzzers
 
 systemd includes fuzzers in `src/fuzz/` that use libFuzzer and are automatically

docs/TESTING_WITH_SANITIZERS.md

@@ -13,6 +13,22 @@ This is mostly done automagically by various CI systems for each PR, but you may
 want to do it locally as well. The process slightly varies depending on the
 compiler you want to use and which part of the test suite you want to run.
 
+## mkosi
+
+To build with sanitizers in mkosi, create a file 20-local.conf in mkosi.default.d/ and add the following
+contents:
+
+```
+[Content]
+Environment=SANITIZERS=address,undefined
+```
+
+The value of `SANITIZERS` is passed directly to meson's `b_sanitize` option, See
+https://mesonbuild.com/Builtin-options.html#base-options for the format expected by the option. Currently,
+only the sanitizers supported by gcc can be used, which are `address` and `undefined`.
+
+Note that this will only work with a recent version of mkosi (>= 14 or by running mkosi directly from source).
+
 ## gcc
 gcc compiles in sanitizer libraries dynamically by default, so you need to get
 the shared libraries first - on Fedora these are shipped as a separate packages