RFC Unifying LKL into UML

This is another spin of the unification of LKL into UML. Updated and fixed comments from our v7 patches. The summary is listed in the changelog below.

Note that the whole patchset requires the patch "um: ubd: fix command line handling of ubd" to be correctly tested, which I previously submitted.

Changes in rfc v8:
- stop using the term "nommu" mode, "library" mode instead
- generic atomic64 rewrite to use gcc builtin atomics
- use kernel-doc format for comments
- stop using a collection of function pointer (struct lkl_host_operations), but weak functions
- use python3, not python
- use c99 initializers for strerror
- add comments/descriptions about thread implementation
- remove redundant Kconfig entries (RAID6_PQ_BENCHMARK, STACKTRACE_SUPPORT, etc)
- refine code comments
- stop using NPROC for the internal -j flag
- remove make argument of "UMMODE=library"
- preserve the vmlinux file as it is
- rework commit history with reasonable files
- rework test framework using kselftest (tools/testing/selftests/um/)
- add documentation, MAINTAINERS

Changes in rfc v7:
- preserve make ARCH=um syntax to build UML
- introduce make ARCH=um UMMODE=library to build library mode
- fix undefined symbols issue during modpost
- clean up makefiles (arch/um, tools/um)

Changes in rfc v6:
- rebase with the current linus tree

Changes in rfc v5:
- rewrite whole patchset from scratch
- move arch-dependent code of arch/um and arch/x86/um to tools/um
- mainly code under os-Linux/ involved
- introduce 2-stage build (kernel, and host-dependent parts)
- clean up vmlinux.lds.S
- put LKL-specific implementations as a SUBARCH under arch/um/nommu
- introduce !CONFIG_MMU in arch/um
- use struct arch_thread and arch_switch_to() for subarch-specific thread implementation
- integrate with the IRQ infrastructure of UML
- tested with block device drivers (ubd) for the proof

Changes in rfc v4: (https://lwn.net/Articles/816276/)
- Rebase on the current uml/master branch
- Fix IRQ handling (bug fix)
- drop a patch for CONFIG_GENERIC_ATOMIC64 (comment by Peter Zijlstra)
- implement vector net driver for UMMODE_LIB (comment by Anton)
- clean up uapi headers to avoid duplicates
- clean up IRQ handling code (comment by Anton)
- fix error handling in test code (comments by David Disseldorp)

Changes in rfc v3:
- use UML drivers (net, block) from LKL programs
- drop virtio device implementations
- drop mingw32 (Windows) host
- drop android (arm/aarch64) host
- drop FreeBSD (x86_64) host
- drop LD_PRELOAD (hijack) support
- update milestone

rfc v2:
- use UMMODE instead of SUBARCH to switch UML or LKL
- tools/lkl directory is still there. I confirmed we can move under arch/um (e.g., arch/um/lkl/hosts). I will move it IF this is preferable.
- drop several patches involved non-uml directory
- drop several patches which are not required
- refine commit logs
- document updated

LKL (Linux Kernel Library) is aiming to allow reusing the Linux kernel code as extensively as possible with minimal effort and reduced maintenance overhead.

Examples of how LKL can be used are: creating userspace applications (running on Linux and other operating systems) that can read or write Linux filesystems or can use the Linux networking stack, creating kernel drivers for other operating systems that can read Linux filesystems, bootloaders support for reading/writing Linux filesystems, etc.

With LKL, the kernel code is compiled into an object file that can be directly linked by applications. The API offered by LKL is based on the Linux system call interface.

LKL is originally implemented as an architecture port in arch/lkl, but this series of commits tries to integrate this into arch/um as one of the mode of UML. This was discussed during RFC email of LKL (*1).

The latest LKL version can be found at https://github.com/lkl/linux

Milestone
=========
This patches is a first step toward upstreaming *library mode* of Linux kernel, but we think we need to have several steps toward our goal, describing in the below.

Milestone 1: LKL lib on top of UML
* Kernel - Host build split
- Build UML as a relocatable object using the UML's kernel linker script.
- Move the ptrace and other well isolated os code out of arch/um to tools/um
- Use standard host toolchain to create a static library stripped of the ptrace code. Use standard host toolchain to build the main UML executable.
- Add library init API that creates the UML kernel process and starts UML.
* System calls APIs
- Add new system call interface based on UML's irq facility.
- Use the LKL scripts to export the required headers to create system calls APIs that use the UML system calls infrastructure.
- Keep the underlying host and driver operations (threads, irqs, etc.) as they are now in UML.
* Boot test
- Port the LKL boot test to verify that we are able to programatically issue system calls.

Milestone 2: add virtio disk support
* Export asm/io.h operations to host/os. Create IO access operations and redirect them to weak os_ variants that use the current UML implementation.
* Add the LKL IO access layer including generic virtio handling and the virtio block device code.
* Port LKL disk test and disk apps (lklfuse, fs2tar, cptofs)

Milestone 3: new arch ports
* Abstract the system call / IRQ mode the move the implementation to host
* Abstract the thread model and move the implementation to host
* Add LKL thread model and LKL ports

Building LKL the host library and LKL applications
==================================================

% make ARCH=um SUBARCH=lkl defconfig
% make ARCH=um SUBARCH=lkl

will build LKL as a object file, it will install it in tools/um/libtogether with the headers files in tools/um/include then will build the host library, tests and a few of application examples:

* tools/testing/selftests/um/boot.c - a simple applications that uses LKL and exercises the basic LKL APIs

* tools/testing/selftests/um/disk.c - a simple applications that tests LKL and exercises the basic filesystem-related LKL APIs

Those tests can run with the following kselftest command:

    $ make ARCH=um SUBARCH=lkl TARGETS="um" kselftest

Supported hosts
===============

Currently LKL supports Linux userspace applications. New hosts can be added relatively easy if the host supports gcc and GNU ld. Previous versions of LKL supported Windows kernel and Haiku kernel hosts, and we also have WIP patches with rump-hypercall interface, used in UEFI, as well as macOS userspace (part of POSIX).

There is also musl-libc port for LKL, which might be interested in for some folks.

Further readings about LKL
=========================

- Discussion in github LKL issue
https://github.com/lkl/linux/issues/304

- LKL (an article)
https://www.researchgate.net/profile/Nicolae_Tapus2/publication/224164682_LKL_The_Linux_kernel_library/links/02bfe50fd921ab4f7c000000.pdf

*1 RFC email to LKML (back in 2015)
https://www.mail-archive.com/[email protected]/msg1012277.html

Please review the following changes for suitability for inclusion. If you have any objections or suggestions for improvement, please respond to the patches. If you agree with the changes, please provide your Acked-by.

The following changes since commit 19c329f6808995b142b3966301f217c831e7cf31:

Linux 5.11-rc4 (2021-01-17 16:37:05 -0800)

are available in the Git repository at:

git://github.com/thehajime/linux 043677211bb5562397c511911e7861c3e217611b
https://github.com/thehajime/linux/tree/uml-lkl-5.11rc4-v8

Hajime Tazaki (18):
um: move arch/um/os-Linux dir to tools/um/uml
um: move arch/x86/um/os-Linux to tools/um/uml/
um: extend arch_switch_to for alternate SUBARCH
um: add UML library mode
um: lkl: host interface
um: lkl: memory handling
um: lkl: kernel thread support
um: lkl: system call interface and application API
um: lkl: basic console support
um: lkl: initialization and cleanup
um: lkl: integrate with irq infrastructure of UML
um: lkl: plug in the build system
um: host: add library mode build for ARCH=um
um: host: add utilities functions
um: host: posix host operations
selftests/um: lkl: add test programs for library mode of UML
um: lkl: add block device support of UML
um: lkl: add documentation

Octavian Purdila (2):
um: split build in kernel and host parts
um: implement os_initcalls and os_exitcalls

 Documentation/virt/uml/lkl.txt                |  48 ++
 MAINTAINERS                                   |  10 +
 arch/um/Kconfig                               |  37 +-
 arch/um/Makefile                              |  41 +-
 arch/um/configs/lkl_defconfig                 |  73 +++
 arch/um/drivers/Makefile                      |  10 +-
 .../um/{os-Linux => }/drivers/ethertap_kern.c |   0
 arch/um/{os-Linux => }/drivers/tuntap_kern.c  |   0
 arch/um/include/asm/common.lds.S              |  99 ----
 arch/um/include/asm/host_ops.h                |   9 +
 arch/um/include/asm/mmu.h                     |   3 +
 arch/um/include/asm/mmu_context.h             |  10 +
 arch/um/include/asm/page.h                    |  15 +
 arch/um/include/asm/pgtable.h                 |  27 +
 arch/um/include/asm/thread_info.h             |  24 +
 arch/um/include/asm/uaccess.h                 |   6 +
 arch/um/include/asm/xor.h                     |   3 +-
 arch/um/include/shared/as-layout.h            |   1 +
 .../drivers => include/shared}/etap.h         |   0
 arch/um/include/shared/init.h                 |  19 +-
 arch/um/include/shared/os.h                   |   1 +
 .../drivers => include/shared}/tuntap.h       |   0
 arch/um/kernel/Makefile                       |  13 +-
 arch/um/kernel/dyn.lds.S                      | 171 -------
 arch/um/kernel/irq.c                          |  13 +
 arch/um/kernel/process.c                      |  14 +-
 arch/um/kernel/reboot.c                       |   5 +
 arch/um/kernel/time.c                         |   2 +
 arch/um/kernel/um_arch.c                      |  16 +
 arch/um/kernel/uml.lds.S                      | 115 -----
 arch/um/{os-Linux => kernel}/user_syms.c      |   0
 arch/um/kernel/vmlinux.lds.S                  |  92 +++-
 arch/um/lkl/Makefile                          |   2 +
 arch/um/lkl/Makefile.um                       |  18 +
 arch/um/lkl/include/asm/Kbuild                |   7 +
 arch/um/lkl/include/asm/archparam.h           |   1 +
 arch/um/lkl/include/asm/atomic.h              |  11 +
 arch/um/lkl/include/asm/atomic64.h            |  91 ++++
 arch/um/lkl/include/asm/cpu.h                 |  15 +
 arch/um/lkl/include/asm/elf.h                 |  19 +
 arch/um/lkl/include/asm/mm_context.h          |   8 +
 arch/um/lkl/include/asm/processor.h           |  48 ++
 arch/um/lkl/include/asm/ptrace.h              |  21 +
 arch/um/lkl/include/asm/sched.h               |  23 +
 arch/um/lkl/include/asm/segment.h             |   9 +
 arch/um/lkl/include/asm/syscall_wrapper.h     |  57 +++
 arch/um/lkl/include/asm/syscalls.h            |  15 +
 arch/um/lkl/include/uapi/asm/Kbuild           |   6 +
 arch/um/lkl/include/uapi/asm/bitsperlong.h    |  16 +
 arch/um/lkl/include/uapi/asm/byteorder.h      |  13 +
 arch/um/lkl/include/uapi/asm/host_ops.h       | 280 +++++++++++
 arch/um/lkl/include/uapi/asm/sigcontext.h     |  12 +
 arch/um/lkl/include/uapi/asm/syscalls.h       | 301 ++++++++++++
 arch/um/lkl/include/uapi/asm/unistd.h         |  17 +
 arch/um/lkl/um/Kconfig                        |  21 +
 arch/um/lkl/um/Makefile                       |   4 +
 arch/um/lkl/um/bootmem.c                      | 107 ++++
 arch/um/lkl/um/console.c                      |  41 ++
 arch/um/lkl/um/cpu.c                          | 269 ++++++++++
 arch/um/lkl/um/delay.c                        |  31 ++
 arch/um/lkl/um/setup.c                        | 179 +++++++
 arch/um/lkl/um/shared/sysdep/archsetjmp.h     |  13 +
 arch/um/lkl/um/shared/sysdep/faultinfo.h      |   8 +
 arch/um/lkl/um/shared/sysdep/kernel-offsets.h |  12 +
 arch/um/lkl/um/shared/sysdep/mcontext.h       |   9 +
 arch/um/lkl/um/shared/sysdep/ptrace.h         |  42 ++
 arch/um/lkl/um/shared/sysdep/ptrace_user.h    |   7 +
 arch/um/lkl/um/syscalls.c                     | 193 ++++++++
 arch/um/lkl/um/threads.c                      | 261 ++++++++++
 arch/um/lkl/um/unimplemented.c                |  70 +++
 arch/um/lkl/um/user_constants.h               |  13 +
 arch/um/os-Linux/Makefile                     |  21 -
 arch/um/os-Linux/drivers/Makefile             |  13 -
 arch/um/scripts/headers_install.py            | 200 ++++++++
 arch/x86/um/Makefile                          |   2 +-
 arch/x86/um/os-Linux/Makefile                 |  13 -
 arch/x86/um/ptrace_32.c                       |   2 +-
 arch/x86/um/syscalls_64.c                     |   2 +-
 scripts/headers_install.sh                    |   6 +-
 scripts/link-vmlinux.sh                       |  42 +-
 tools/testing/selftests/Makefile              |   3 +
 tools/testing/selftests/um/Makefile           |  16 +
 tools/testing/selftests/um/boot.c             | 376 ++++++++++++++
 tools/testing/selftests/um/cla.c              | 159 ++++++
 tools/testing/selftests/um/cla.h              |  33 ++
 tools/testing/selftests/um/disk-ext4.sh       |   6 +
 tools/testing/selftests/um/disk-vfat.sh       |   6 +
 tools/testing/selftests/um/disk.c             | 166 +++++++
 tools/testing/selftests/um/disk.sh            |  67 +++
 tools/testing/selftests/um/test.c             | 128 +++++
 tools/testing/selftests/um/test.h             |  72 +++
 tools/testing/selftests/um/test.sh            | 181 +++++++
 tools/um/.gitignore                           |   1 +
 tools/um/Makefile                             |  76 +++
 tools/um/Targets                              |   9 +
 tools/um/include/lkl.h                        | 364 ++++++++++++++
 tools/um/include/lkl_host.h                   |  19 +
 tools/um/lib/Build                            |   7 +
 tools/um/lib/fs.c                             | 461 ++++++++++++++++++
 tools/um/lib/jmp_buf.c                        |  14 +
 tools/um/lib/posix-host.c                     | 273 +++++++++++
 tools/um/lib/utils.c                          | 207 ++++++++
 tools/um/uml/Build                            |  59 +++
 tools/um/uml/drivers/Build                    |  10 +
 .../um/uml}/drivers/ethertap_user.c           |   0
 .../um/uml}/drivers/tuntap_user.c             |   0
 {arch/um/os-Linux => tools/um/uml}/elf_aux.c  |   0
 {arch/um/os-Linux => tools/um/uml}/execvp.c   |   4 -
 {arch/um/os-Linux => tools/um/uml}/file.c     |   0
 {arch/um/os-Linux => tools/um/uml}/helper.c   |   0
 {arch/um/os-Linux => tools/um/uml}/irq.c      |   0
 tools/um/uml/lkl/Build                        |   1 +
 tools/um/uml/lkl/registers.c                  |  21 +
 tools/um/uml/lkl/unimplemented.c              |  21 +
 {arch/um/os-Linux => tools/um/uml}/main.c     |   0
 {arch/um/os-Linux => tools/um/uml}/mem.c      |   0
 {arch/um/os-Linux => tools/um/uml}/process.c  |   2 +
 .../um/os-Linux => tools/um/uml}/registers.c  |   0
 {arch/um/os-Linux => tools/um/uml}/sigio.c    |   0
 {arch/um/os-Linux => tools/um/uml}/signal.c   |  12 +-
 .../skas/Makefile => tools/um/uml/skas/Build  |   6 +-
 {arch/um/os-Linux => tools/um/uml}/skas/mem.c |   0
 .../os-Linux => tools/um/uml}/skas/process.c  |   3 +-
 {arch/um/os-Linux => tools/um/uml}/start_up.c |   0
 {arch/um/os-Linux => tools/um/uml}/time.c     |   0
 {arch/um/os-Linux => tools/um/uml}/tty.c      |   0
 {arch/um/os-Linux => tools/um/uml}/umid.c     |   0
 {arch/um/os-Linux => tools/um/uml}/util.c     |  26 +
 tools/um/uml/x86/Build                        |  11 +
 .../os-Linux => tools/um/uml/x86}/mcontext.c  |   0
 .../um/os-Linux => tools/um/uml/x86}/prctl.c  |   0
 .../os-Linux => tools/um/uml/x86}/registers.c |   0
 .../os-Linux => tools/um/uml/x86}/task_size.c |   0
 .../um/os-Linux => tools/um/uml/x86}/tls.c    |   0
 134 files changed, 5743 insertions(+), 525 deletions(-)
 create mode 100644 Documentation/virt/uml/lkl.txt
 create mode 100644 arch/um/configs/lkl_defconfig
 rename arch/um/{os-Linux => }/drivers/ethertap_kern.c (100%)
 rename arch/um/{os-Linux => }/drivers/tuntap_kern.c (100%)
 delete mode 100644 arch/um/include/asm/common.lds.S
 create mode 100644 arch/um/include/asm/host_ops.h
 rename arch/um/{os-Linux/drivers => include/shared}/etap.h (100%)
 rename arch/um/{os-Linux/drivers => include/shared}/tuntap.h (100%)
 delete mode 100644 arch/um/kernel/dyn.lds.S
 delete mode 100644 arch/um/kernel/uml.lds.S
 rename arch/um/{os-Linux => kernel}/user_syms.c (100%)
 create mode 100644 arch/um/lkl/Makefile
 create mode 100644 arch/um/lkl/Makefile.um
 create mode 100644 arch/um/lkl/include/asm/Kbuild
 create mode 100644 arch/um/lkl/include/asm/archparam.h
 create mode 100644 arch/um/lkl/include/asm/atomic.h
 create mode 100644 arch/um/lkl/include/asm/atomic64.h
 create mode 100644 arch/um/lkl/include/asm/cpu.h
 create mode 100644 arch/um/lkl/include/asm/elf.h
 create mode 100644 arch/um/lkl/include/asm/mm_context.h
 create mode 100644 arch/um/lkl/include/asm/processor.h
 create mode 100644 arch/um/lkl/include/asm/ptrace.h
 create mode 100644 arch/um/lkl/include/asm/sched.h
 create mode 100644 arch/um/lkl/include/asm/segment.h
 create mode 100644 arch/um/lkl/include/asm/syscall_wrapper.h
 create mode 100644 arch/um/lkl/include/asm/syscalls.h
 create mode 100644 arch/um/lkl/include/uapi/asm/Kbuild
 create mode 100644 arch/um/lkl/include/uapi/asm/bitsperlong.h
 create mode 100644 arch/um/lkl/include/uapi/asm/byteorder.h
 create mode 100644 arch/um/lkl/include/uapi/asm/host_ops.h
 create mode 100644 arch/um/lkl/include/uapi/asm/sigcontext.h
 create mode 100644 arch/um/lkl/include/uapi/asm/syscalls.h
 create mode 100644 arch/um/lkl/include/uapi/asm/unistd.h
 create mode 100644 arch/um/lkl/um/Kconfig
 create mode 100644 arch/um/lkl/um/Makefile
 create mode 100644 arch/um/lkl/um/bootmem.c
 create mode 100644 arch/um/lkl/um/console.c
 create mode 100644 arch/um/lkl/um/cpu.c
 create mode 100644 arch/um/lkl/um/delay.c
 create mode 100644 arch/um/lkl/um/setup.c
 create mode 100644 arch/um/lkl/um/shared/sysdep/archsetjmp.h
 create mode 100644 arch/um/lkl/um/shared/sysdep/faultinfo.h
 create mode 100644 arch/um/lkl/um/shared/sysdep/kernel-offsets.h
 create mode 100644 arch/um/lkl/um/shared/sysdep/mcontext.h
 create mode 100644 arch/um/lkl/um/shared/sysdep/ptrace.h
 create mode 100644 arch/um/lkl/um/shared/sysdep/ptrace_user.h
 create mode 100644 arch/um/lkl/um/syscalls.c
 create mode 100644 arch/um/lkl/um/threads.c
 create mode 100644 arch/um/lkl/um/unimplemented.c
 create mode 100644 arch/um/lkl/um/user_constants.h
 delete mode 100644 arch/um/os-Linux/Makefile
 delete mode 100644 arch/um/os-Linux/drivers/Makefile
 create mode 100755 arch/um/scripts/headers_install.py
 delete mode 100644 arch/x86/um/os-Linux/Makefile
 create mode 100644 tools/testing/selftests/um/Makefile
 create mode 100644 tools/testing/selftests/um/boot.c
 create mode 100644 tools/testing/selftests/um/cla.c
 create mode 100644 tools/testing/selftests/um/cla.h
 create mode 100755 tools/testing/selftests/um/disk-ext4.sh
 create mode 100755 tools/testing/selftests/um/disk-vfat.sh
 create mode 100644 tools/testing/selftests/um/disk.c
 create mode 100755 tools/testing/selftests/um/disk.sh
 create mode 100644 tools/testing/selftests/um/test.c
 create mode 100644 tools/testing/selftests/um/test.h
 create mode 100644 tools/testing/selftests/um/test.sh
 create mode 100644 tools/um/.gitignore
 create mode 100644 tools/um/Makefile
 create mode 100644 tools/um/Targets
 create mode 100644 tools/um/include/lkl.h
 create mode 100644 tools/um/include/lkl_host.h
 create mode 100644 tools/um/lib/Build
 create mode 100644 tools/um/lib/fs.c
 create mode 100644 tools/um/lib/jmp_buf.c
 create mode 100644 tools/um/lib/posix-host.c
 create mode 100644 tools/um/lib/utils.c
 create mode 100644 tools/um/uml/Build
 create mode 100644 tools/um/uml/drivers/Build
 rename {arch/um/os-Linux => tools/um/uml}/drivers/ethertap_user.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/drivers/tuntap_user.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/elf_aux.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/execvp.c (98%)
 rename {arch/um/os-Linux => tools/um/uml}/file.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/helper.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/irq.c (100%)
 create mode 100644 tools/um/uml/lkl/Build
 create mode 100644 tools/um/uml/lkl/registers.c
 create mode 100644 tools/um/uml/lkl/unimplemented.c
 rename {arch/um/os-Linux => tools/um/uml}/main.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/mem.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/process.c (99%)
 rename {arch/um/os-Linux => tools/um/uml}/registers.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/sigio.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/signal.c (96%)
 rename arch/um/os-Linux/skas/Makefile => tools/um/uml/skas/Build (56%)
 rename {arch/um/os-Linux => tools/um/uml}/skas/mem.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/skas/process.c (99%)
 rename {arch/um/os-Linux => tools/um/uml}/start_up.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/time.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/tty.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/umid.c (100%)
 rename {arch/um/os-Linux => tools/um/uml}/util.c (89%)
 create mode 100644 tools/um/uml/x86/Build
 rename {arch/x86/um/os-Linux => tools/um/uml/x86}/mcontext.c (100%)
 rename {arch/x86/um/os-Linux => tools/um/uml/x86}/prctl.c (100%)
 rename {arch/x86/um/os-Linux => tools/um/uml/x86}/registers.c (100%)
 rename {arch/x86/um/os-Linux => tools/um/uml/x86}/task_size.c (100%)
 rename {arch/x86/um/os-Linux => tools/um/uml/x86}/tls.c (100%)

2.21.0 (Apple Git-122.2)


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