Commit acc08b51 authored by Sam Ravnborg's avatar Sam Ravnborg

kbuild: document environment variables

Add kbuild.txt to Documentation/kbuild
More stuff can be added later - at least we have
som of the varous environment variables documented now.
Signed-off-by: default avatarSam Ravnborg <sam@ravnborg.org>
parent 2af238e4
00-INDEX
- this file: info on the kernel build process
- this file: info on the kernel build process
kbuild.txt
- developer information on kbuild
kconfig.txt
- usage help for make *config
kconfig-language.txt
- specification of Config Language, the language in Kconfig files
makefiles.txt
- developer information for linux kernel makefiles
kconfig.txt
- usage help for make *config
modules.txt
- how to build modules and to install them
Environment variables
KCPPFLAGS
--------------------------------------------------
Additional options to pass when preprocessing. The preprocessing options
will be used in all cases where kbuild do preprocessing including
building C files and assembler files.
KAFLAGS
--------------------------------------------------
Additional options to the assembler.
KCFLAGS
--------------------------------------------------
Additional options to the C compiler.
KBUILD_VERBOSE
--------------------------------------------------
Set the kbuild verbosity. Can be assinged same values as "V=...".
See make help for the full list.
Setting "V=..." takes precedence over KBUILD_VERBOSE.
KBUILD_EXTMOD
--------------------------------------------------
Set the directory to look for the kernel source when building external
modules.
The directory can be specified in several ways:
1) Use "M=..." on the command line
2) Environmnet variable KBUILD_EXTMOD
3) Environmnet variable SUBDIRS
The possibilities are listed in the order they take precedence.
Using "M=..." will always override the others.
KBUILD_OUTPUT
--------------------------------------------------
Specify the output directory when building the kernel.
The output directory can also be specificed using "O=...".
Setting "O=..." takes precedence over KBUILD_OUTPUT
ARCH
--------------------------------------------------
Set ARCH to the architecture to be built.
In most cases the name of the architecture is the same as the
directory name found in the arch/ directory.
But some architectures suach as x86 and sparc has aliases.
x86: i386 for 32 bit, x86_64 for 64 bit
sparc: sparc for 32 bit, sparc64 for 64 bit
CROSS_COMPILE
--------------------------------------------------
Specify an optional fixed part of the binutils filename.
CROSS_COMPILE can be a part of the filename or the full path.
CROSS_COMPILE is also used for ccache is some setups.
CF
--------------------------------------------------
Additional options for sparse.
CF is often used on the command-line like this:
make CF=-Wbitwise C=2
INSTALL_PATH
--------------------------------------------------
INSTALL_PATH specifies where to place the updated kernel and system map
images. Default is /boot, but you can set it to other values
MODLIB
--------------------------------------------------
Specify where to install modules.
The default value is:
$(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
The value can be overridden in which case the default value is ignored.
INSTALL_MOD_PATH
--------------------------------------------------
INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
relocations required by build roots. This is not defined in the
makefile but the argument can be passed to make if needed.
INSTALL_MOD_STRIP
--------------------------------------------------
INSTALL_MOD_STRIP, if defined, will cause modules to be
stripped after they are installed. If INSTALL_MOD_STRIP is '1', then
the default option --strip-debug will be used. Otherwise,
INSTALL_MOD_STRIP will used as the options to the strip command.
INSTALL_FW_PATH
--------------------------------------------------
INSTALL_FW_PATH specify where to install the firmware blobs.
The default value is:
$(INSTALL_MOD_PATH)/lib/firmware
The value can be overridden in which case the default value is ignored.
INSTALL_HDR_PATH
--------------------------------------------------
INSTALL_HDR_PATH specify where to install user space headers when
executing "make headers_*".
The default value is:
$(objtree)/usr
$(objtree) is the directory where output files are saved.
The output directory is often set using "O=..." on the commandline.
The value can be overridden in which case the default value is ignored.
KBUILD_MODPOST_WARN
--------------------------------------------------
KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined
symbols in the final module linking stage.
KBUILD_MODPOST_FINAL
--------------------------------------------------
KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
This is solely usefull to speed up test compiles.
KBUILD_EXTRA_SYMBOLS
--------------------------------------------------
For modules use symbols from another modules.
See more details in modules.txt.
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