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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 <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>
270 lines
7.4 KiB
ReStructuredText
270 lines
7.4 KiB
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======
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Kbuild
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======
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Output files
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============
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modules.order
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-------------
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This file records the order in which modules appear in Makefiles. This
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is used by modprobe to deterministically resolve aliases that match
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multiple modules.
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modules.builtin
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---------------
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This file lists all modules that are built into the kernel. This is used
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by modprobe to not fail when trying to load something builtin.
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modules.builtin.modinfo
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-----------------------
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This file contains modinfo from all modules that are built into the kernel.
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Unlike modinfo of a separate module, all fields are prefixed with module name.
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Environment variables
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=====================
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KCPPFLAGS
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---------
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Additional options to pass when preprocessing. The preprocessing options
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will be used in all cases where kbuild does preprocessing including
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building C files and assembler files.
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KAFLAGS
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-------
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Additional options to the assembler (for built-in and modules).
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AFLAGS_MODULE
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-------------
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Additional assembler options for modules.
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AFLAGS_KERNEL
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-------------
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Additional assembler options for built-in.
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KCFLAGS
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-------
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Additional options to the C compiler (for built-in and modules).
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CFLAGS_KERNEL
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-------------
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Additional options for $(CC) when used to compile
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code that is compiled as built-in.
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CFLAGS_MODULE
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-------------
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Additional module specific options to use for $(CC).
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LDFLAGS_MODULE
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--------------
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Additional options used for $(LD) when linking modules.
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HOSTCFLAGS
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----------
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Additional flags to be passed to $(HOSTCC) when building host programs.
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HOSTCXXFLAGS
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------------
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Additional flags to be passed to $(HOSTCXX) when building host programs.
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HOSTLDFLAGS
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-----------
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Additional flags to be passed when linking host programs.
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HOSTLDLIBS
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----------
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Additional libraries to link against when building host programs.
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KBUILD_KCONFIG
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--------------
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Set the top-level Kconfig file to the value of this environment
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variable. The default name is "Kconfig".
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KBUILD_VERBOSE
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--------------
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Set the kbuild verbosity. Can be assigned same values as "V=...".
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See make help for the full list.
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Setting "V=..." takes precedence over KBUILD_VERBOSE.
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KBUILD_EXTMOD
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-------------
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Set the directory to look for the kernel source when building external
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modules.
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Setting "M=..." takes precedence over KBUILD_EXTMOD.
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KBUILD_OUTPUT
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-------------
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Specify the output directory when building the kernel.
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The output directory can also be specified using "O=...".
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Setting "O=..." takes precedence over KBUILD_OUTPUT.
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KBUILD_EXTRA_WARN
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-----------------
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Specify the extra build checks. The same value can be assigned by passing
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W=... from the command line.
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See `make help` for the list of the supported values.
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Setting "W=..." takes precedence over KBUILD_EXTRA_WARN.
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KBUILD_DEBARCH
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--------------
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For the deb-pkg target, allows overriding the normal heuristics deployed by
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deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
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the UTS_MACHINE variable, and on some architectures also the kernel config.
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The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
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architecture.
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ARCH
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----
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Set ARCH to the architecture to be built.
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In most cases the name of the architecture is the same as the
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directory name found in the arch/ directory.
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But some architectures such as x86 and sparc have aliases.
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- x86: i386 for 32 bit, x86_64 for 64 bit
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- sh: sh for 32 bit, sh64 for 64 bit
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- sparc: sparc32 for 32 bit, sparc64 for 64 bit
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CROSS_COMPILE
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-------------
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Specify an optional fixed part of the binutils filename.
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CROSS_COMPILE can be a part of the filename or the full path.
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CROSS_COMPILE is also used for ccache in some setups.
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CF
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--
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Additional options for sparse.
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CF is often used on the command-line like this::
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make CF=-Wbitwise C=2
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INSTALL_PATH
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------------
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INSTALL_PATH specifies where to place the updated kernel and system map
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images. Default is /boot, but you can set it to other values.
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INSTALLKERNEL
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-------------
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Install script called when using "make install".
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The default name is "installkernel".
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The script will be called with the following arguments:
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- $1 - kernel version
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- $2 - kernel image file
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- $3 - kernel map file
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- $4 - default install path (use root directory if blank)
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The implementation of "make install" is architecture specific
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and it may differ from the above.
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INSTALLKERNEL is provided to enable the possibility to
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specify a custom installer when cross compiling a kernel.
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MODLIB
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------
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Specify where to install modules.
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The default value is::
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$(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
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The value can be overridden in which case the default value is ignored.
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INSTALL_MOD_PATH
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----------------
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INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
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relocations required by build roots. This is not defined in the
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makefile but the argument can be passed to make if needed.
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INSTALL_MOD_STRIP
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-----------------
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INSTALL_MOD_STRIP, if defined, will cause modules to be
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stripped after they are installed. If INSTALL_MOD_STRIP is '1', then
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the default option --strip-debug will be used. Otherwise,
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INSTALL_MOD_STRIP value will be used as the options to the strip command.
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INSTALL_HDR_PATH
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----------------
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INSTALL_HDR_PATH specifies where to install user space headers when
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executing "make headers_*".
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The default value is::
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$(objtree)/usr
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$(objtree) is the directory where output files are saved.
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The output directory is often set using "O=..." on the commandline.
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The value can be overridden in which case the default value is ignored.
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KBUILD_ABS_SRCTREE
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--------------------------------------------------
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Kbuild uses a relative path to point to the tree when possible. For instance,
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when building in the source tree, the source tree path is '.'
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Setting this flag requests Kbuild to use absolute path to the source tree.
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There are some useful cases to do so, like when generating tag files with
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absolute path entries etc.
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KBUILD_SIGN_PIN
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---------------
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This variable allows a passphrase or PIN to be passed to the sign-file
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utility when signing kernel modules, if the private key requires such.
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KBUILD_MODPOST_WARN
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-------------------
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KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
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symbols in the final module linking stage. It changes such errors
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into warnings.
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KBUILD_MODPOST_NOFINAL
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----------------------
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KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
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This is solely useful to speed up test compiles.
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KBUILD_EXTRA_SYMBOLS
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--------------------
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For modules that use symbols from other modules.
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See more details in modules.rst.
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ALLSOURCE_ARCHS
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---------------
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For tags/TAGS/cscope targets, you can specify more than one arch
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to be included in the databases, separated by blank space. E.g.::
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$ make ALLSOURCE_ARCHS="x86 mips arm" tags
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To get all available archs you can also specify all. E.g.::
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$ make ALLSOURCE_ARCHS=all tags
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KBUILD_BUILD_TIMESTAMP
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----------------------
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Setting this to a date string overrides the timestamp used in the
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UTS_VERSION definition (uname -v in the running kernel). The value has to
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be a string that can be passed to date -d. The default value
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is the output of the date command at one point during build.
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KBUILD_BUILD_USER, KBUILD_BUILD_HOST
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------------------------------------
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These two variables allow to override the user@host string displayed during
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boot and in /proc/version. The default value is the output of the commands
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whoami and host, respectively.
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LLVM
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----
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If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
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of GCC and GNU binutils to build the kernel.
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