qemu-user clone syscall fails

[Aaron Simmons]

qemu-user fails to emulate clone() (https://linux.die.net/man/2/clone). The architecture doesn't seem to matter, tho I've mostly been testing aarch64.

Attached is clone_test.c that demonstrates the problem. Running it natively looks like this:
$ bin/x86_64/clone_test
The variable was 9
clone returned 4177: 0 Success
The variable is now 42

However, running it via qemu looks like:
$ qemu-aarch64-static --version
qemu-aarch64 version 5.2.0 (v5.2.0)
Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers

$ qemu-aarch64-static bin/aarch64/clone_test
The variable was 9
clone returned -1: 22 Invalid argument
The variable is now 9

[Aaron Simmons (paleozogt)]

clone_test aarch64 binary

[Aaron Simmons (paleozogt)]

clone_test x86_64 binary

[Aaron Simmons (paleozogt)]

clone_test (aarch64)

[Aaron Simmons (paleozogt)]

clone_test (x86_64)

[Alex Bennée (ajbennee)]

I suspect it's failing because the qemu-user emulation of clone is basically enough for what libc uses and not for your own set of flags:

  https://qemu-project.gitlab.io/qemu/src/S/2440.html#L6478

[Alex Bennée (ajbennee)]

For a full explanation see: https://qemu-project.gitlab.io/qemu/src/S/2440.html#L141

[Thomas Huth (th-huth)]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know how to transfer the bug to the new system if
(if still necessary). For this we're setting the status to "Incomplete"
now.

In the unlikely case that the bug has already been fixed in the latest
upstream version of QEMU, then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here should be
moved to the new system, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

    https://gitlab.com/qemu-project/qemu/-/issues

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" or "Confirmed" within the next 60 days (other-
wise it will get closed as "Expired"). We will then eventually migrate
the ticket automatically to the new system (but you won't be the reporter
of the bug in the new system and thus you won't get notified on changes
anymore).

Thank you and sorry for the inconvenience.

[Launchpad Janitor (janitor)]

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