kbuild: document environment variables

00-INDEX

	- 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.