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performance: 0.727
device: 0.723
files: 0.661
debug: 0.624
semantic: 0.547
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PID: 0.458
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graphic: 0.441
network: 0.422
vnc: 0.395
KVM: 0.192

qemu-aarch64 hangs on cptofs during a build of NixOS SD card image

First, thank you for this incredible project.

While following this guide to build my own image of NixOS: https://nixos.wiki/wiki/NixOS_on_ARM#Compiling_through_QEMU on ARM Aarch64.

I encountered a very strange behavior, qemu is correctly used and build most of the binaries until it executes this exact line over qemu: https://github.com/NixOS/nixpkgs/blob/master/nixos/lib/make-ext4-fs.nix#L55

At this step, the qemu process goes to 100 % of CPU, hangs in a certain syscall I don't know which one (according to strace & gdb which has no symbols so breaking and looking the backtrace was useless).

According to iotop, no I/O was done.

And it spent all its time in this syscall during more than 10 hours, which looks anomalous to me.

I attach some of my CPU info:

model		: 142
model name	: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
stepping	: 10
microcode	: 0x96
cpu MHz		: 3107.071
cache size	: 8192 KB

I'm using a ThinkPad T480 to perform those builds, I'm uncertain of how to debug further this issue, I discussed this with some people over #nixos-aarch64 and they told me they didn't know how to debug it further too.

I tried all with this package: https://aur.archlinux.org/packages/qemu-arm-static/ — I'm currently compiling qemu-git to see if it happens on upstream too. Will comment when it's done.

Thank you in advance!

Update: compiling qemu upstream & using the latest version didn't change anything.


I don't know if this is an instance of user emulation limitations due to missing syscalls.

The QEMU project is currently considering to move its bug tracking to
another system. For this we need to know which bugs are still valid
and which could be closed already. Thus we are setting older bugs to
"Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.


[Expired for QEMU because there has been no activity for 60 days.]