linux.git/arch/um/kernel/Makefile, branch v7.0

um: Add initial SMP support

2025-10-27T15:41:15+00:00

Add initial symmetric multi-processing (SMP) support to UML. With
this support enabled, users can tell UML to start multiple virtual
processors, each represented as a separate host thread.

In UML, kthreads and normal threads (when running in kernel mode)
can be scheduled and executed simultaneously on different virtual
processors. However, the userspace code of normal threads still
runs within their respective single-threaded stubs.

That is, SMP support is currently available both within the kernel
and across different processes, but still remains limited within
threads of the same process in userspace.

Signed-off-by: Tiwei Bie 
Link: https://patch.msgid.link/20251027001815.1666872-6-tiwei.bie@linux.dev
Signed-off-by: Johannes Berg

Merge tag 'kbuild-v6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

2025-06-07T17:05:35+00:00

Pull Kbuild updates from Masahiro Yamada:

 - Add support for the EXPORT_SYMBOL_GPL_FOR_MODULES() macro, which
   exports a symbol only to specified modules

 - Improve ABI handling in gendwarfksyms

 - Forcibly link lib-y objects to vmlinux even if CONFIG_MODULES=n

 - Add checkers for redundant or missing  inclusion

 - Deprecate the extra-y syntax

 - Fix a genksyms bug when including enum constants from *.symref files

* tag 'kbuild-v6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (28 commits)
  genksyms: Fix enum consts from a reference affecting new values
  arch: use always-$(KBUILD_BUILTIN) for vmlinux.lds
  kbuild: set y instead of 1 to KBUILD_{BUILTIN,MODULES}
  efi/libstub: use 'targets' instead of extra-y in Makefile
  module: make __mod_device_table__* symbols static
  scripts/misc-check: check unnecessary #include  when W=1
  scripts/misc-check: check missing #include  when W=1
  scripts/misc-check: add double-quotes to satisfy shellcheck
  kbuild: move W=1 check for scripts/misc-check to top-level Makefile
  scripts/tags.sh: allow to use alternative ctags implementation
  kconfig: introduce menu type enum
  docs: symbol-namespaces: fix reST warning with literal block
  kbuild: link lib-y objects to vmlinux forcibly even when CONFIG_MODULES=n
  tinyconfig: enable CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
  docs/core-api/symbol-namespaces: drop table of contents and section numbering
  modpost: check forbidden MODULE_IMPORT_NS("module:") at compile time
  kbuild: move kbuild syntax processing to scripts/Makefile.build
  Makefile: remove dependency on archscripts for header installation
  Documentation/kbuild: Add new gendwarfksyms kABI rules
  Documentation/kbuild: Drop section numbers
  ...

arch: use always-$(KBUILD_BUILTIN) for vmlinux.lds

2025-06-07T05:38:07+00:00

The extra-y syntax is deprecated. Instead, use always-$(KBUILD_BUILTIN),
which behaves equivalently.

Signed-off-by: Masahiro Yamada 
Acked-by: Johannes Berg 
Reviewed-by: Nicolas Schier

um: stop using PCI port I/O

2025-06-02T09:22:09+00:00

arch/um is one of the last users of CONFIG_GENERIC_IOMAP, but upon
closer look it appears that the PCI host bridge does not register
any port I/O, and the absense of both custom inb/outb functions and
a PCI_IOBASE constant means that actually trying to use port I/O
results on a NULL pointer access.

Build testing with clang confirms this by warning about this exact
problem:

include/asm-generic/io.h:549:31: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]
  549 |         val = __raw_readb(PCI_IOBASE + addr);
      |                           ~~~~~~~~~~ ^

Remove all the Kconfig selects that refer to legacy port I/O
and instead just build the normal MMIO path that is emulated
by the virtio PCI host.

Signed-off-by: Arnd Bergmann 
Link: https://patch.msgid.link/20250509084125.1488601-1-arnd@kernel.org
Signed-off-by: Johannes Berg

um: remove copy_from_kernel_nofault_allowed

2025-03-18T10:03:29+00:00

There is no need to override the default version of this function
anymore as UML now has proper _nofault memory access functions.

Doing this also fixes the fact that the implementation was incorrect as
using mincore() will incorrectly flag pages as inaccessible if they were
swapped out by the host.

Fixes: f75b1b1bedfb ("um: Implement probe_kernel_read()")
Signed-off-by: Benjamin Berg 
Link: https://patch.msgid.link/20250210160926.420133-3-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg

kbuild: use $(src) instead of $(srctree)/$(src) for source directory

2024-05-09T19:34:52+00:00

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

    src := $(obj)

When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.

This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.

To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.

Going forward, the variables used in Makefiles will have the following
meanings:

  $(obj)     - directory in the object tree
  $(src)     - directory in the source tree  (changed by this commit)
  $(objtree) - the top of the kernel object tree
  $(srctree) - the top of the kernel source tree

Consequently, $(srctree)/$(src) in upstream Makefiles need to be replaced
with $(src).

Signed-off-by: Masahiro Yamada 
Reviewed-by: Nicolas Schier

kbuild: remove --include-dir MAKEFLAG from top Makefile

2023-02-05T09:51:22+00:00

I added $(srctree)/ to some included Makefiles in the following commits:

 - 3204a7fb98a3 ("kbuild: prefix $(srctree)/ to some included Makefiles")
 - d82856395505 ("kbuild: do not require sub-make for separate output tree builds")

They were a preparation for removing --include-dir flag.

I have never thought --include-dir useful. Rather, it _is_ harmful.

For example, run the following commands:

  $ make -s ARCH=x86 mrproper defconfig
  $ make ARCH=arm O=foo dtbs
  make[1]: Entering directory '/tmp/linux/foo'
    HOSTCC  scripts/basic/fixdep
  Error: kernelrelease not valid - run 'make prepare' to update it
    UPD     include/config/kernel.release
  make[1]: Leaving directory '/tmp/linux/foo'

The first command configures the source tree for x86. The next command
tries to build ARM device trees in the separate foo/ directory - this
must stop because the directory foo/ has not been configured yet.

However, due to --include-dir=$(abs_srctree), the top Makefile includes
the wrong include/config/auto.conf from the source tree and continues
building. Kbuild traverses the directory tree, but of course it does
not work correctly. The Error message is also pointless - 'make prepare'
does not help at all for fixing the issue.

This commit fixes more arch Makefile, and finally removes --include-dir
from the top Makefile.

There are more breakages under drivers/, but I do not volunteer to fix
them all. I just moved --include-dir to drivers/Makefile.

With this commit, the second command will stop with a sensible message.

  $ make -s ARCH=x86 mrproper defconfig
  $ make ARCH=arm O=foo dtbs
  make[1]: Entering directory '/tmp/linux/foo'
    SYNC    include/config/auto.conf.cmd
  ***
  *** The source tree is not clean, please run 'make ARCH=arm mrproper'
  *** in /tmp/linux
  ***
  make[2]: *** [../Makefile:646: outputmakefile] Error 1
  /tmp/linux/Makefile:770: include/config/auto.conf.cmd: No such file or directory
  make[1]: *** [/tmp/linux/Makefile:793: include/config/auto.conf.cmd] Error 2
  make[1]: Leaving directory '/tmp/linux/foo'
  make: *** [Makefile:226: __sub-make] Error 2

Signed-off-by: Masahiro Yamada

um: Add devicetree support

2021-12-22T19:35:01+00:00

Add a dtb= option to boot UML with a devicetree blob.  This
can be used for testing driver code using UML.

Signed-off-by: Vincent Whitchurch 
[rw: Add dependency on CONFIG_OF]
Signed-off-by: Richard Weinberger

um: Extract load file helper from initrd.c

2021-12-22T19:32:36+00:00

The file loading support in initrd.c can be re-used for
loading devicetrees.  Move it out of initrd.c.

Signed-off-by: Vincent Whitchurch 
Signed-off-by: Richard Weinberger

um: move amd64 variant of mmap(2) to arch/x86/um/syscalls_64.c

2021-12-21T20:30:44+00:00

Signed-off-by: Al Viro 
Signed-off-by: Richard Weinberger