Daan De Meyer
6891016149
Two complementary changes in the developer-mode branch of meson.build:
1. -ffunction-sections -fdata-sections: pair with the existing
-Wl,--gc-sections so the linker can drop unused individual functions
and data instead of being forced to pull whole .o files into each
binary. Biggest impact on statically-linked NSS/PAM modules (a single
call into creds-util.c used to drag in the entire creds-util
translation unit, which transitively pulled TPM2, OpenSSL, PKCS11 and
KDF helpers via tpm2-util.c / openssl-util.c) and on tests that embed
daemon objects via meson's objects: extraction.
2. -gz=zstd + -fdebug-types-section + -Wl,--compress-debug-sections=zstd:
compress every .debug_* section with zstd, and move type DIEs into a
COMDAT-mergeable section so identical types described across many TUs
land once. Both are transparent to GDB / readelf / addr2line.
Gated to mode == 'developer' for now: no major distro (Fedora, Debian/
Ubuntu, Arch, Alpine, Gentoo, openSUSE, Yocto) enables -ffunction-sections
in their system-wide default CFLAGS, and the interaction with -flto=auto +
-ffat-lto-objects (which Fedora et al. ship by default) deserves a broader
evaluation before turning it on for release builds. Developer mode benefits
straightforwardly: smaller plugins, smaller tests, smaller libraries, no
interference with the hardening/LTO flag combinations distros pin.
Size impact on a clean developer-mode build, 626 ELF objects:
| Category | n | Before | After | Δ | % |
| -------------------------- | --: | ----------: | ----------: | --------------: | ----: |
| NSS plugins | 4 | 22,163,272 | 6,681,120 | −15,482,152 | −69.9 |
| PAM plugins | 3 | 18,132,160 | 5,764,880 | −12,367,280 | −68.2 |
| libsystemd.so (public ABI) | 1 | 6,009,360 | 3,350,168 | −2,659,192 | −44.3 |
| libudev.so (public ABI) | 1 | 4,379,336 | 1,441,256 | −2,938,080 | −67.1 |
| libsystemd-shared-261.so | 1 | 15,130,264 | 11,293,952 | −3,836,312 | −25.4 |
| libsystemd-core-261.so | 1 | 7,356,408 | 4,992,600 | −2,363,808 | −32.1 |
| cryptsetup-token plugins | 3 | 139,800 | 113,344 | −26,456 | −18.9 |
| daemons / CLI tools | 178 | 43,581,288 | 31,911,368 | −11,669,920 | −26.8 |
| test binaries | 386 | 124,717,072 | 60,185,904 | −64,531,168 | −51.7 |
| fuzzers | 48 | 33,138,056 | 13,864,952 | −19,273,104 | −58.2 |
| **TOTAL** | 626 | 274,747,016 | 139,599,544 | **−135,147,472** | **−49.2** |
Biggest individual wins:
| Binary | Before | After | Δ |
| ------------------------ | -------: | -------: | -----: |
| test-networkd-address | 6.21 MB | 0.82 MB | −86.8% |
| test-network-tables | 6.23 MB | 0.85 MB | −86.4% |
| test-networkd-conf | 6.27 MB | 1.32 MB | −78.9% |
| libnss_myhostname.so.2 | 6.40 MB | 1.53 MB | −76.1% |
| fuzz-netdev-parser | 6.22 MB | 1.51 MB | −75.7% |
| fuzz-network-parser | 6.22 MB | 1.70 MB | −72.6% |
| libnss_systemd.so.2 | 6.90 MB | 2.04 MB | −70.4% |
| libnss_resolve.so.2 | 4.42 MB | 1.38 MB | −68.8% |
| pam_systemd_home.so | 6.91 MB | 2.22 MB | −67.9% |
| libudev.so.1.7.13 | 4.18 MB | 1.37 MB | −67.1% |
| pam_systemd.so | 7.02 MB | 2.55 MB | −63.6% |
| libsystemd-shared-261.so | 14.43 MB | 10.77 MB | −25.4% |
The big test wins come from the ~30 daemons (systemd-networkd,
systemd-resolved, systemd-journald, systemd-logind, systemd-homed,
systemd-importd, systemd-machined, …) whose compiled .o files are embedded
directly into their unit tests via meson's objects: extraction mechanism.
With per-function sections on the daemon sources, the test binary can GC
the bulk of code it never exercises; the remaining DWARF is then shared
zstd-compressed across every .o.
Build-speed cost is below noise on a 24-core build: across four clean
builds (with-flags / sections-only / baseline / with-flags rerun) the
range was 23.6–26.0 s real time and 7m39s–7m48s user time, with the
two with-flags runs faster than the baseline by a couple of seconds —
overhead from per-function-section bookkeeping and zstd compression
disappears into parallel-build noise.
System and Service Manager
Details
Most documentation is available on systemd's web site.
Assorted, older, general information about systemd can be found in the systemd Wiki.
Information about build requirements is provided in the README file.
Consult our NEWS file for information about what's new in the most recent systemd versions.
Please see the Code Map for information about this repository's layout and content.
Please see the Hacking guide for information on how to hack on systemd and test your modifications.
Please see our Contribution Guidelines for more information about filing GitHub Issues and posting GitHub Pull Requests.
When preparing patches for systemd, please follow our Coding Style Guidelines.
If you are looking for support, please contact our mailing list, join our IRC channel #systemd on libera.chat or Matrix channel
Stable branches with backported patches are available in the stable repo.
We have a security bug bounty program sponsored by the Sovereign Tech Fund hosted on YesWeHack
Repositories with distribution packages built from git main are available on OBS, and also repositories with packages built from the latest stable release