WARNING::BUILDID(7stap)

💖 WARNING::BUILDID 💖

okay so bestie, welcome to warning::buildid — the page about build-id verification failures 💅. It lives in the 7stap manual (systemtap girlies rise up 🫶), and it's basically the group chat where systemtap tells you "hey… this binary is not the one I thought it was."

✨ DESCRIPTION ✨

So here's the tea ☕: systemtap's script translation / execution stages can happen at different times and different places. Like, translate here, run there, whenever, wherever — main character energy but make it distributed 🌈. Because of that, sometimes it has to verify certain invariants. And one of those invariants is: if a script was informed by translate-time analysis of executables, then those same executables need to be used at run time. No substitutions, no swapsies, periodt ✋.

How does it check? Based on the build-id — a binary hash that modern (post-2007) compilers/toolchains add as an NT_GNU_BUILD_ID ELF note to object files and executables 🎀. If you're curious (and honestly, iconic of you), use the readelf -n command to examine the build-ids of binaries. Go look, bestie, they're right there 👀.

Not every script cares, though. Only scripts are sensitive to executables' build-ids — generally those that perform deep analysis of the binaries or their debuginfo. For example:

• scripts that place .function or .statement probes 🌸
• scripts that use stack backtrace-related tapset functions

those ones may be sensitive. Other scripts that rely only on process.mark or kernel.trace probes do not require debuginfo, so they're just chilling 😌. See the DWARF DEBUGINFO section in the stapprobes(3stap) man page for the full lore.

🧚 what actually happens under the hood

During translation, systemtap saves a copy of the relevant files' build-ids within the compiled modules 💾. Then at run-time, the modules compare the saved ones to the actual run-time build-ids in memory. If the warning message pops up, that means they did not match 😭 — so the module will decline placing a probe that was computed based upon obsolete data.

And that's actually a good thing!! Because placing them at an inappropriate address could crash the programs 💀. Safety first, always.

But ngl, it's not necessarily a fatal error — because probes unrelated to the mismatching binaries may still operate just fine. So it's giving "partial slay, partial oops" 🙈.

🔥 why would this even happen

A build-id mismatch could be caused by a few different situations. The main one is when the executable versions or architecture were different between the systemtap translation and execution times/places 👑. Like:

• one may run a stap-server on a slightly different version of the OS distribution 🦋
• someone may have rebuilt a new kernel image, but preserved the previous version numbers (sneaky!!)
• the kernel running on the workstation may be slightly different from the version being targeted — perhaps due to a pending kernel upgrade leaving different files on disk versus running in memory 🌸
• if your OS distribution uses separate debuginfo packages, the split .debug files may not exactly match the main binaries 💔

💅 how to make it stop

To disable build-id verification warnings — if one is confident that they are an artefact of build accidents rather than a real mismatch — one might try the -DSTP_NO_BUILDID_CHECK option ✨.

fr fr though: only do that if you're sure it's just build chaos and not a real mismatch, bestie. Confidence required 💖.

🌟 SEE ALSO 🌟

• http://fedoraproject.org/wiki/Releases/FeatureBuildId
• stap(1)
• stapprobes(3stap)
• warning::debuginfo(7stap)
• error::reporting(7stap)

okay that's the whole page, you ate that reading it 💖✨ this was WARNING::BUILDID(7stap) from the 7stap manual section, so go forth and go be iconic with your build-ids 🎀🦋👑