[Bug 1829459] Re: qemu seems to lack support for pid namespace.

[Laurent Vivier]

PID namespace prevents to execute some syscalls, even if you use --map-
root-user. This is managed at kernel level by the capabilities.

Could you try to do the exact same thing with the native architecture
binaries in the chroot to see if the problem really comes from qemu-
user?

Could you try to use the latest unshare version (util-linux package)
that adds a "--keep-caps" parameter (v2.35-rc1) to preserve the
capabilities?

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https://bugs.launchpad.net/bugs/1829459

Title:
  qemu seems to lack support for pid namespace.

Status in QEMU:
  New

Bug description:
  # Version

  qemu-4.0.0
  glibc-2.28

  # commands used to launch qemu-aarch64 in user mode.

  : ${QEMU_BINFMT_FLAGS:=OC}

  printf '%s\n' ':qemu-
  
aarch64:M::\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xb7\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin
  /qemu-aarch64:'"${QEMU_BINFMT_FLAGS}"
  >/proc/sys/fs/binfmt_misc/register

  > sudo cp /usr/bin/qemu-aarch64 $RPI/usr/bin
  > sudo chroot $RPI /bin/ksh -l

  # host

  Gentoo Linux amd64

  # Guest

  Gentoo Linux aarch64

  # The problem that I have

  "emerge" program fails due to the error, "qemu: qemu_thread_create: Invalid 
argument".
  "emerge" is Gentoo's package manager that compiles and installs packages.

  # Workaround

  Disable pid-sandbox in emerge.

  # How to reproduce the issue

  Execute

  unshare --pid -- echo hello world

  or

  python -c "import portage.process; portage.process.spawn(['echo',
  'hello', 'world'], unshare_pid=True)"

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