[Bug 1926996] [NEW] qemu-user clone syscall fails

[Aaron Simmons]

Public bug reported:

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

** Affects: qemu
     Importance: Undecided
         Status: New

** Attachment added: "clone_test.c"
   
https://bugs.launchpad.net/bugs/1926996/+attachment/5494466/+files/clone_test.c

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https://bugs.launchpad.net/bugs/1926996

Title:
  qemu-user clone syscall fails

Status in QEMU:
  New

Bug description:
  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

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