SD-DLOPEN(3)

💖 SD-DLOPEN 💖

okay bestie, gather round, because this one is genuinely cute and also extremely niche. this is the manual page for sd-dlopen, aka the ELF dlopen metadata annotation macros. yes the name is a mouthful. yes it slays anyway. let's go 🦋

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✨ NAME ✨

sd-dlopen — the ELF dlopen metadata annotation macros. that's it, that's the whole vibe. 💅

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✨ SYNOPSIS ✨

#include <systemd/sd-dlopen.h>

pkg-config --cflags libsystemd

like, that's literally all you need. no linking, no drama, no build system tears. 🫶

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✨ DESCRIPTION ✨

so here's the tea: sd-dlopen.h hands you a bunch of macros that let you embed .note.dlopen metadata straight into your ELF binaries. it's the implementation of the ELF dlopen metadata[^1] specification, and what that spec does is let you declare optional shared library dependencies — the ones you load at runtime via dlopen(3) instead of at link time. iykyk. 👑

and the best part? the header is self-contained. it does not require runtime linkage against libsystemd(3). nope. projects literally only need the installed header to use the macros. that's it. no cap. 🎀

why does anyone care, you ask? because package managers and build systems can read the embedded ELF notes and discover runtime dependencies that are completely invisible in ELF DT_NEEDED entries. sneaky little deps, exposed. iconic behavior honestly. 🔥

if you want the full rundown on which macros and constants are available, go read SD_ELF_NOTE_DLOPEN(3). that's where the actual macro menu lives. 📖

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✨ NOTES ✨

• the macros described here are header-only — they do not require runtime linkage against libsystemd(3)
• all you need is the installed header and the include path, exactly as handed to you by pkg-config --cflags libsystemd

bestie this is the whole point: it's giving "zero runtime dependency" energy and we are obsessed. 💖

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✨ HISTORY ✨

SD_ELF_NOTE_DLOPEN() and its associated macros and constants showed up in version 261. so if you're on something older, that's why it's not working, and no it's not your fault. 🌸

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✨ SEE ALSO ✨

• systemd(1)
• SD_ELF_NOTE_DLOPEN(3)
• dlopen(3)

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✨ NOTES ✨

1. ELF dlopen metadata — https://uapi-group.org/specifications/specs/elf_dlopen_metadata/

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and that's the whole page, bestie!! this was systemd 262.1, brought to you with love and also with sd-dlopen energy. go forth and annotate your ELF binaries. periodt. 💜✨

[^1]: yes the footnote is the spec link up there, i put it in the NOTES section where it belongs because we do not skip details in this house 🎀