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

[-]

The same issue persists in qemu-5.2.0.

-----------------------------------------
# qemu-aarch64 --version
qemu-aarch64 version 5.2.0
Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers
-----------------------------------------

Symptoms when running inside the aarch64 chroot, with both aarch64 and x86_64 
binaries:
-----------------------------------------
# which unshare bash
/usr/bin/unshare
/bin/bash
# file $(!!)
file $(which unshare bash)
/usr/bin/unshare: ELF 64-bit LSB pie executable, ARM aarch64, version 1 (SYSV), 
dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, for GNU/Linux 
3.7.0, stripped
/bin/bash:        ELF 64-bit LSB pie executable, ARM aarch64, version 1 (SYSV), 
dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, for GNU/Linux 
3.7.0, stripped
# unshare --pid -- bash -c 'echo hello world'
qemu: qemu_thread_create: Invalid argument
Aborted (core dumped)
# # --- switch to an x86_64 shell _inside_ the chroot
# LD_LIBRARY_PATH=/x86_64/lib64 PATH=/x86_64/bin:$PATH bash 
# which unshare bash
/x86_64/bin/unshare
/x86_64/bin/bash
# file $(!!)
file $(which unshare bash)
/x86_64/bin/unshare: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), 
dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 
3.2.0, stripped
/x86_64/bin/bash:    ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), 
dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 
3.2.0, stripped
# unshare --pid -- bash -c 'echo hello world' 
hello world
# 
-----------------------------------------

I can share the core dump, in case that's useful.

On this system, the qemu-aarch64 binary on the host is statically built
and binfmt_misc is configured as follows:
-----------------------------------------
:aarch64:M::\x7f\x45\x4c\x46\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xb7:\xff\xff\xff\xff\xff\xff\xff\xfc\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/usr/bin/qemu-aarch64:CF
-----------------------------------------

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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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