linux.git/Documentation/kbuild, branch v5.7

Documentation: kbuild: fix the section title format

2020-04-23T01:53:19+00:00

Make it consistent with the other sections.

Signed-off-by: Masahiro Yamada

kbuild: support LLVM=1 to switch the default tools to Clang/LLVM

2020-04-08T18:18:21+00:00

As Documentation/kbuild/llvm.rst implies, building the kernel with a
full set of LLVM tools gets very verbose and unwieldy.

Provide a single switch LLVM=1 to use Clang and LLVM tools instead
of GCC and Binutils. You can pass it from the command line or as an
environment variable.

Please note LLVM=1 does not turn on the integrated assembler. You need
to pass LLVM_IAS=1 to use it. When the upstream kernel is ready for the
integrated assembler, I think we can make it default.

We discussed what we need, and we agreed to go with a simple boolean
flag that switches both target and host tools:

  https://lkml.org/lkml/2020/3/28/494
  https://lkml.org/lkml/2020/4/3/43

Some items discussed, but not adopted:

- LLVM_DIR

  When multiple versions of LLVM are installed, I just thought supporting
  LLVM_DIR=/path/to/my/llvm/bin/ might be useful.

  CC      = $(LLVM_DIR)clang
  LD      = $(LLVM_DIR)ld.lld
    ...

  However, we can handle this by modifying PATH. So, we decided to not do
  this.

- LLVM_SUFFIX

  Some distributions (e.g. Debian) package specific versions of LLVM with
  naming conventions that use the version as a suffix.

  CC      = clang$(LLVM_SUFFIX)
  LD      = ld.lld(LLVM_SUFFIX)
    ...

  will allow a user to pass LLVM_SUFFIX=-11 to use clang-11 etc.,
  but the suffixed versions in /usr/bin/ are symlinks to binaries in
  /usr/lib/llvm-#/bin/, so this can also be handled by PATH.

Signed-off-by: Masahiro Yamada 
Reviewed-by: Nathan Chancellor 
Tested-by: Nathan Chancellor  # build
Tested-by: Nick Desaulniers 
Reviewed-by: Nick Desaulniers

kbuild: replace AS=clang with LLVM_IAS=1

2020-04-08T18:18:09+00:00

The 'AS' variable is unused for building the kernel. Only the remaining
usage is to turn on the integrated assembler. A boolean flag is a better
fit for this purpose.

AS=clang was added for experts. So, I replaced it with LLVM_IAS=1,
breaking the backward compatibility.

Suggested-by: Nick Desaulniers 
Signed-off-by: Masahiro Yamada 
Reviewed-by: Nathan Chancellor 
Reviewed-by: Nick Desaulniers

Documentation/llvm: fix the name of llvm-size

2020-04-08T15:13:45+00:00

The tool is called llvm-size, not llvm-objsize.

Fixes: fcf1b6a35c16 ("Documentation/llvm: add documentation on building w/ Clang/LLVM")
Signed-off-by: Fangrui Song 
Reviewed-by: Nick Desaulniers 
Reviewed-by: Nathan Chancellor 
Signed-off-by: Masahiro Yamada

Merge tag 'kbuild-v5.7' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

2020-03-31T23:03:39+00:00

Pull Kbuild updates from Masahiro Yamada:
 "Build system:

   - add CONFIG_UNUSED_KSYMS_WHITELIST, which will be useful to define a
     fixed set of export symbols for Generic Kernel Image (GKI)

   - allow to run 'make dt_binding_check' without .config

   - use full schema for checking DT examples in *.yaml files

   - make modpost fail for missing MODULE_IMPORT_NS(), which makes more
     sense because we know the produced modules are never loadable

   - Remove unused 'AS' variable

  Kconfig:

   - sanitize DEFCONFIG_LIST, and remove ARCH_DEFCONFIG from Kconfig
     files

   - relax the 'imply' behavior so that symbols implied by 'y' can
     become 'm'

   - make 'imply' obey 'depends on' in order to make 'imply' really weak

  Misc:

   - add documentation on building the kernel with Clang/LLVM

   - revive __HAVE_ARCH_STRLEN for 32bit sparc to use optimized strlen()

   - fix warning from deb-pkg builds when CONFIG_DEBUG_INFO=n

   - various script and Makefile cleanups"

* tag 'kbuild-v5.7' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (34 commits)
  Makefile: Update kselftest help information
  kbuild: deb-pkg: fix warning when CONFIG_DEBUG_INFO is unset
  kbuild: add outputmakefile to no-dot-config-targets
  kbuild: remove AS variable
  net: wan: wanxl: refactor the firmware rebuild rule
  net: wan: wanxl: use $(M68KCC) instead of $(M68KAS) for rebuilding firmware
  net: wan: wanxl: use allow to pass CROSS_COMPILE_M68k for rebuilding firmware
  kbuild: add comment about grouped target
  kbuild: add -Wall to KBUILD_HOSTCXXFLAGS
  kconfig: remove unused variable in qconf.cc
  sparc: revive __HAVE_ARCH_STRLEN for 32bit sparc
  kbuild: refactor Makefile.dtbinst more
  kbuild: compute the dtbs_install destination more simply
  Makefile: disallow data races on gcc-10 as well
  kconfig: make 'imply' obey the direct dependency
  kconfig: allow symbols implied by y to become m
  net: drop_monitor: use IS_REACHABLE() to guard net_dm_hw_report()
  modpost: return error if module is missing ns imports and MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS=n
  modpost: rework and consolidate logging interface
  kbuild: allow to run dt_binding_check without kernel configuration
  ...

Merge tag 'docs-5.7' of git://git.lwn.net/linux

2020-03-30T19:45:23+00:00

Pull documentation updates from Jonathan Corbet:
 "This has been a busy cycle for documentation work.

  Highlights include:

   - Lots of RST conversion work by Mauro, Daniel ALmeida, and others.
     Maybe someday we'll get to the end of this stuff...maybe...

   - Some organizational work to bring some order to the core-api
     manual.

   - Various new docs and additions to the existing documentation.

   - Typo fixes, warning fixes, ..."

* tag 'docs-5.7' of git://git.lwn.net/linux: (123 commits)
  Documentation: x86: exception-tables: document CONFIG_BUILDTIME_TABLE_SORT
  MAINTAINERS: adjust to filesystem doc ReST conversion
  docs: deprecated.rst: Add BUG()-family
  doc: zh_CN: add translation for virtiofs
  doc: zh_CN: index files in filesystems subdirectory
  docs: locking: Drop :c:func: throughout
  docs: locking: Add 'need' to hardirq section
  docs: conf.py: avoid thousands of duplicate label warning on Sphinx
  docs: prevent warnings due to autosectionlabel
  docs: fix reference to core-api/namespaces.rst
  docs: fix pointers to io-mapping.rst and io_ordering.rst files
  Documentation: Better document the softlockup_panic sysctl
  docs: hw-vuln: tsx_async_abort.rst: get rid of an unused ref
  docs: perf: imx-ddr.rst: get rid of a warning
  docs: filesystems: fuse.rst: supress a Sphinx warning
  docs: translations: it: avoid duplicate refs at programming-language.rst
  docs: driver.rst: supress two ReSt warnings
  docs: trace: events.rst: convert some new stuff to ReST format
  Documentation: Add io_ordering.rst to driver-api manual
  Documentation: Add io-mapping.rst to driver-api manual
  ...

modpost: move the namespace field in Module.symvers last

2020-03-16T23:59:03+00:00

In order to preserve backwards compatability with kmod tools, we have to
move the namespace field in Module.symvers last, as the depmod -e -E
option looks at the first three fields in Module.symvers to check symbol
versions (and it's expected they stay in the original order of crc,
symbol, module).

In addition, update an ancient comment above read_dump() in modpost that
suggested that the export type field in Module.symvers was optional. I
suspect that there were historical reasons behind that comment that are
no longer accurate. We have been unconditionally printing the export
type since 2.6.18 (commit bd5cbcedf44), which is over a decade ago now.

Fix up read_dump() to treat each field as non-optional. I suspect the
original read_dump() code treated the export field as optional in order
to support pre <= 2.6.18 Module.symvers (which did not have the export
type field). Note that although symbol namespaces are optional, the
field will not be omitted from Module.symvers if a symbol does not have
a namespace. In this case, the field will simply be empty and the next
delimiter or end of line will follow.

Cc: stable@vger.kernel.org
Fixes: cb9b55d21fe0 ("modpost: add support for symbol namespaces")
Tested-by: Matthias Maennich 
Reviewed-by: Matthias Maennich 
Reviewed-by: Lucas De Marchi 
Signed-off-by: Jessica Yu 
Signed-off-by: Masahiro Yamada

kconfig: make 'imply' obey the direct dependency

2020-03-13T01:05:34+00:00

The 'imply' statement may create unmet direct dependency when the
implied symbol depends on m.

[Test Code]

  config FOO
          tristate "foo"
          imply BAZ

  config BAZ
          tristate "baz"
          depends on BAR

  config BAR
          def_tristate m

  config MODULES
          def_bool y
          option modules

If you set FOO=y, BAZ is also promoted to y, which results in the
following .config file:

  CONFIG_FOO=y
  CONFIG_BAZ=y
  CONFIG_BAR=m
  CONFIG_MODULES=y

This does not meet the dependency 'BAZ depends on BAR'.

Unlike 'select', what is worse, Kconfig never shows the
'WARNING: unmet direct dependencies detected for ...' for this case.

Because 'imply' is considered to be weaker than 'depends on', Kconfig
should take the direct dependency into account.

For clarification, describe this case in kconfig-language.rst too.

Signed-off-by: Masahiro Yamada 
Acked-by: Nicolas Pitre 
Tested-by: Geert Uytterhoeven

kconfig: allow symbols implied by y to become m

2020-03-13T01:05:34+00:00

The 'imply' keyword restricts a symbol to y or n, excluding m
when it is implied by y. This is the original behavior since
commit 237e3ad0f195 ("Kconfig: Introduce the "imply" keyword").

However, the author of this feature, Nicolas Pitre, stated that
the 'imply' keyword should not impose any restrictions.
(https://lkml.org/lkml/2020/2/19/714)

I agree, and want to get rid of this tricky behavior.

Suggested-by: Nicolas Pitre 
Signed-off-by: Masahiro Yamada 
Acked-by: Nicolas Pitre

kbuild: doc: fix references to other documents

2020-03-13T01:02:27+00:00

All the files in Documentation/kbuild/ were converted to reST.

Signed-off-by: Masahiro Yamada