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/2020/3/28/494https://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 <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
KBUILD_ENABLE_EXTRA_GCC_CHECKS started as a switch to add extra warning
options for GCC, but now it is a historical misnomer since we use it
also for Clang, DTC, and even kernel-doc.
Rename it to more sensible, shorter KBUILD_EXTRA_WARN.
For the backward compatibility, KBUILD_ENABLE_EXTRA_GCC_CHECKS is still
supported (but not advertised in the documentation).
I also fixed up 'make help', and updated the documentation.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
These three variables are not intended to be tweaked by users.
Move them from kbuild.rst to makefiles.rst.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
- match the directory structure of the linux-libc-dev package to that of
Debian-based distributions
- fix incorrect include/config/auto.conf generation when Kconfig creates
it along with the .config file
- remove misleading $(AS) from documents
- clean up precious tag files by distclean instead of mrproper
- add a new coccinelle patch for devm_platform_ioremap_resource migration
- refactor module-related scripts to read modules.order instead of
$(MODVERDIR)/*.mod files to get the list of created modules
- remove MODVERDIR
- update list of header compile-test
- add -fcf-protection=none flag to avoid conflict with the retpoline
flags when CONFIG_RETPOLINE=y
- misc cleanups
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Merge tag 'kbuild-v5.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull more Kbuild updates from Masahiro Yamada:
- match the directory structure of the linux-libc-dev package to that
of Debian-based distributions
- fix incorrect include/config/auto.conf generation when Kconfig
creates it along with the .config file
- remove misleading $(AS) from documents
- clean up precious tag files by distclean instead of mrproper
- add a new coccinelle patch for devm_platform_ioremap_resource
migration
- refactor module-related scripts to read modules.order instead of
$(MODVERDIR)/*.mod files to get the list of created modules
- remove MODVERDIR
- update list of header compile-test
- add -fcf-protection=none flag to avoid conflict with the retpoline
flags when CONFIG_RETPOLINE=y
- misc cleanups
* tag 'kbuild-v5.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (25 commits)
kbuild: add -fcf-protection=none when using retpoline flags
kbuild: update compile-test header list for v5.3-rc1
kbuild: split out *.mod out of {single,multi}-used-m rules
kbuild: remove 'prepare1' target
kbuild: remove the first line of *.mod files
kbuild: create *.mod with full directory path and remove MODVERDIR
kbuild: export_report: read modules.order instead of .tmp_versions/*.mod
kbuild: modpost: read modules.order instead of $(MODVERDIR)/*.mod
kbuild: modsign: read modules.order instead of $(MODVERDIR)/*.mod
kbuild: modinst: read modules.order instead of $(MODVERDIR)/*.mod
scsi: remove pointless $(MODVERDIR)/$(obj)/53c700.ver
kbuild: remove duplication from modules.order in sub-directories
kbuild: get rid of kernel/ prefix from in-tree modules.{order,builtin}
kbuild: do not create empty modules.order in the prepare stage
coccinelle: api: add devm_platform_ioremap_resource script
kbuild: compile-test headers listed in header-test-m as well
kbuild: remove unused hostcc-option
kbuild: remove tag files by distclean instead of mrproper
kbuild: add --hash-style= and --build-id unconditionally
kbuild: get rid of misleading $(AS) from documents
...
The assembler files in the kernel are *.S instead of *.s, so they must
be preprocessed. Since 'as' of GNU binutils is not able to preprocess,
we always use $(CC) as an assembler driver.
$(AS) is almost unused in Kbuild. As of v5.2, there is just one place
that directly invokes $(AS).
$ git grep -e '$(AS)' -e '${AS}' -e '$AS' -e '$(AS:' -e '${AS:' -- :^Documentation
drivers/net/wan/Makefile: AS68K = $(AS)
The documentation about *_AFLAGS* sounds like the flags were passed
to $(AS). This is somewhat misleading.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
The tag ".. include" should be replaced by ".. literalinclude" at
issues.rst, otherwise it causes TeX to crash due to excessive usage
of stack with Sphinx 2.0.
While here, solve a few minor issues at the kbuild book output by
adding extra blank lines.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
- remove headers_{install,check}_all targets
- remove unreasonable 'depends on !UML' from CONFIG_SAMPLES
- re-implement 'make headers_install' more cleanly
- add new header-test-y syntax to compile-test headers
- compile-test exported headers to ensure they are compilable in
user-space
- compile-test headers under include/ to ensure they are self-contained
- remove -Waggregate-return, -Wno-uninitialized, -Wno-unused-value flags
- add -Werror=unknown-warning-option for Clang
- add 128-bit built-in types support to genksyms
- fix missed rebuild of modules.builtin
- propagate 'No space left on device' error in fixdep to Make
- allow Clang to use its integrated assembler
- improve some coccinelle scripts
- add a new flag KBUILD_ABS_SRCTREE to request Kbuild to use absolute
path for $(srctree).
- do not ignore errors when compression utility is missing
- misc cleanups
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Merge tag 'kbuild-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild updates from Masahiro Yamada:
- remove headers_{install,check}_all targets
- remove unreasonable 'depends on !UML' from CONFIG_SAMPLES
- re-implement 'make headers_install' more cleanly
- add new header-test-y syntax to compile-test headers
- compile-test exported headers to ensure they are compilable in
user-space
- compile-test headers under include/ to ensure they are self-contained
- remove -Waggregate-return, -Wno-uninitialized, -Wno-unused-value
flags
- add -Werror=unknown-warning-option for Clang
- add 128-bit built-in types support to genksyms
- fix missed rebuild of modules.builtin
- propagate 'No space left on device' error in fixdep to Make
- allow Clang to use its integrated assembler
- improve some coccinelle scripts
- add a new flag KBUILD_ABS_SRCTREE to request Kbuild to use absolute
path for $(srctree).
- do not ignore errors when compression utility is missing
- misc cleanups
* tag 'kbuild-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (49 commits)
kbuild: use -- separater intead of $(filter-out ...) for cc-cross-prefix
kbuild: Inform user to pass ARCH= for make mrproper
kbuild: fix compression errors getting ignored
kbuild: add a flag to force absolute path for srctree
kbuild: replace KBUILD_SRCTREE with boolean building_out_of_srctree
kbuild: remove src and obj from the top Makefile
scripts/tags.sh: remove unused environment variables from comments
scripts/tags.sh: drop SUBARCH support for ARM
kbuild: compile-test kernel headers to ensure they are self-contained
kheaders: include only headers into kheaders_data.tar.xz
kheaders: remove meaningless -R option of 'ls'
kbuild: support header-test-pattern-y
kbuild: do not create wrappers for header-test-y
kbuild: compile-test exported headers to ensure they are self-contained
init/Kconfig: add CONFIG_CC_CAN_LINK
kallsyms: exclude kasan local symbols on s390
kbuild: add more hints about SUBDIRS replacement
coccinelle: api/stream_open: treat all wait_.*() calls as blocking
coccinelle: put_device: Add a cast to an expression for an assignment
coccinelle: put_device: Adjust a message construction
...
The kbuild documentation clearly shows that the documents
there are written at different times: some use markdown,
some use their own peculiar logic to split sections.
Convert everything to ReST without affecting too much
the author's style and avoiding adding uneeded markups.
The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Masahiro Yamada