linux_kernel/arch/um/Kconfig.um

# SPDX-License-Identifier: GPL-2.0
config STATIC_LINK
	bool "Force a static link"
	default n
	help
	  This option gives you the ability to force a static link of UML.
	  Normally, UML is linked as a shared binary.  This is inconvenient for
	  use in a chroot jail.  So, if you intend to run UML inside a chroot,
	  you probably want to say Y here.
	  Additionally, this option enables using higher memory spaces (up to
	  2.75G) for UML.

source "mm/Kconfig"

config LD_SCRIPT_STATIC
	bool
	default y
	depends on STATIC_LINK

config LD_SCRIPT_DYN
	bool
	default y
	depends on !LD_SCRIPT_STATIC
        select MODULE_REL_CRCS if MODVERSIONS

source "fs/Kconfig.binfmt"

config HOSTFS
	tristate "Host filesystem"
	help
          While the User-Mode Linux port uses its own root file system for
          booting and normal file access, this module lets the UML user
          access files stored on the host.  It does not require any
          network connection between the Host and UML.  An example use of
          this might be:

          mount none /tmp/fromhost -t hostfs -o /tmp/umlshare

          where /tmp/fromhost is an empty directory inside UML and
          /tmp/umlshare is a directory on the host with files the UML user
          wishes to access.

          For more information, see
          <http://user-mode-linux.sourceforge.net/hostfs.html>.

          If you'd like to be able to work with files stored on the host,
          say Y or M here; otherwise say N.

config MCONSOLE
	bool "Management console"
	depends on PROC_FS
	default y
	help
          The user mode linux management console is a low-level interface to
          the kernel, somewhat like the i386 SysRq interface.  Since there is
          a full-blown operating system running under every user mode linux
          instance, there is much greater flexibility possible than with the
          SysRq mechanism.

          If you answer 'Y' to this option, to use this feature, you need the
          mconsole client (called uml_mconsole) which is present in CVS in
          2.4.5-9um and later (path /tools/mconsole), and is also in the
          distribution RPM package in 2.4.6 and later.

          It is safe to say 'Y' here.

config MAGIC_SYSRQ
	bool "Magic SysRq key"
	depends on MCONSOLE
	help
	  If you say Y here, you will have some control over the system even
	  if the system crashes for example during kernel debugging (e.g., you
	  will be able to flush the buffer cache to disk, reboot the system
	  immediately or dump some status information). A key for each of the
	  possible requests is provided.

	  This is the feature normally accomplished by pressing a key
	  while holding SysRq (Alt+PrintScreen).

	  On UML, this is accomplished by sending a "sysrq" command with
	  mconsole, followed by the letter for the requested command.

	  The keys are documented in <file:Documentation/admin-guide/sysrq.rst>. Don't say Y
	  unless you really know what this hack does.

config KERNEL_STACK_ORDER
	int "Kernel stack size order"
	default 1 if 64BIT
	range 1 10 if 64BIT
	default 0 if !64BIT
	help
	  This option determines the size of UML kernel stacks.  They will
	  be 1 << order pages.  The default is OK unless you're running Valgrind
	  on UML, in which case, set this to 3.

config MMAPPER
	tristate "iomem emulation driver"
	help
	  This driver allows a host file to be used as emulated IO memory inside
	  UML.

config NO_DMA
	def_bool y

config PGTABLE_LEVELS
	int
	default 3 if 3_LEVEL_PGTABLES
	default 2

config SECCOMP
	def_bool y
	prompt "Enable seccomp to safely compute untrusted bytecode"
	---help---
	  This kernel feature is useful for number crunching applications
	  that may need to compute untrusted bytecode during their
	  execution. By using pipes or other transports made available to
	  the process as file descriptors supporting the read/write
	  syscalls, it's possible to isolate those applications in
	  their own address space using seccomp. Once seccomp is
	  enabled via prctl(PR_SET_SECCOMP), it cannot be disabled
	  and the task is only allowed to execute a few safe syscalls
	  defined by each seccomp mode.

	  If unsure, say Y.