Some discussions on #debian-systemd IRC that may or may not be useful.

<mbiebl> plugwash: there is #908658
-zwiebelbot/#debian-systemd- Debian#908658: systemd: apt-get upgrade from 239-7 to 239-8 failed - https://bugs.debian.org/908658
-BTS/#debian-systemd- Closed #908358 in systemd by Michael Biebl (biebl) «Display stays off after computer resumes from suspend». https://bugs.debian.org/908358
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<plugwash> mbiebl, mmm that is just weird, that bug claims it appeared with -8 and went away again with -9 yet there is nothing relavent in the changelog
<plugwash> all I can think is that it was caused by some library at build time.
<mbiebl> that or the compiler
<mbiebl> (or build flags rather)
<mbiebl> not sure if that changed between -7 and -8 (and again between -8 and -9)
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<mbiebl> plugwash: looks like having this library installed trips of MemoryDenyWriteExecute
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<mbiebl> plugwash: if raspi-copies-and-fills fiddles e.g. with the memcpy implementation, it sounds like this could very well be the culprit
<plugwash> <mbiebl> https://raspberrypi.stackexchange.com/questions/72594/failed-to-start-udev-kernel-device-manager <-- i'm aware of that one but this guy claims not to have raspi-copies-and-fills installed, also this guy claims his system works with -7 but not -8 (we don't have -9 in raspbian yet, some of our autobuilders seem unable to successfully run the systemd testsuite) so it seems to be a seperate issue.
<mbiebl> the only relevant changes on the systemd side between -7 and -8 are 
<mbiebl> https://salsa.debian.org/systemd-team/systemd/commit/40dca899f180066a7e72b8fd227b3ad2a9f056ce
<mbiebl> https://salsa.debian.org/systemd-team/systemd/commit/5da767304781d6d06e65a93b8de25d06727faa88
<mbiebl> I don't see how they could trigger this failure.
<plugwash> me neither but I don't think it's something we did either, which leads to a puzzle of what caused this. It's not 100% clear but I don't think https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=908658 was using raspbian as raspbian doesn't have -9 yet.
-zwiebelbot/#debian-systemd- Debian#908658: systemd: apt-get upgrade from 239-7 to 239-8 failed - https://bugs.debian.org/908658
<plugwash> *was not using raspbian
<plugwash> i'm currently in the process of setting up a sacrificial system to try and reproduce this.
<mbiebl> plugwash: hm, Distributor ID: Raspbian
<mbiebl> curious
<mbiebl> some kind of frankendebian?
<mbiebl> raspbian with buster apt source enabled?
<mbiebl> libc6            2.27-5+rpi1 looks like it's not a pristine buster system
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<plugwash> very possibly a system with both Debian and Raspbian apt sources enabled.
<mbiebl> so if 239-8 is provided by raspbian, does it mean it get's recompiled there?
<mbiebl> maybe -8 was build with the raspbian toolchain and -9 came straight from Debian
<mbiebl> which would be some kind of explanation
<plugwash> right, everything in raspbian gets recompiled, there is not enough information in that bug report to know if he was using the Debian built -8 or the raspbian built -8. 
<mbiebl> plugwash: it would be the most logical explanation though, that the failing - 8 version he had installed came from raspbian and not debian
<mbiebl> otherwise I'm completely out of idea why -8 did not work and -9 did
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<mbiebl> plugwash: the user confirmed that -8 was installed from raspbian directly