kbuild: doc: replace arch/$(ARCH)/ with arch/$(SRCARCH)/

	Makefile                    the top Makefile.

	.config                     the kernel configuration file.

	arch/$(ARCH)/Makefile	the arch Makefile.

	arch/$(SRCARCH)/Makefile    the arch Makefile.

	scripts/Makefile.*          common rules etc. for all kbuild Makefiles.

	kbuild Makefiles            exist in every subdirectory

the kernel source tree.

The list of subdirectories which are visited depends upon the kernel

configuration. The top Makefile textually includes an arch Makefile

with the name arch/$(ARCH)/Makefile. The arch Makefile supplies

with the name arch/$(SRCARCH)/Makefile. The arch Makefile supplies

architecture-specific information to the top Makefile.

Each subdirectory has a kbuild Makefile which carries out the commands

and clean as usual. The Makefile located in arch/x86/boot/ may use

the subdir- trick to descend further down.

Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is

Note 1: arch/$(SRCARCH)/Makefile cannot use "subdir-", because that file is

included in the top level makefile, and the kbuild infrastructure

is not operational at that point.

The top level Makefile sets up the environment and does the preparation,

before starting to descend down in the individual directories.

The top level makefile contains the generic part, whereas

arch/$(ARCH)/Makefile contains what is required to set up kbuild

arch/$(SRCARCH)/Makefile contains what is required to set up kbuild

for said architecture.

To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines

To do so, arch/$(SRCARCH)/Makefile sets up a number of variables and defines

a few targets.

When kbuild executes, the following steps are followed (roughly):

1) Configuration of the kernel => produce .config

2) Store kernel version in include/linux/version.h

3) Updating all other prerequisites to the target prepare:

   - Additional prerequisites are specified in arch/$(ARCH)/Makefile

   - Additional prerequisites are specified in arch/$(SRCARCH)/Makefile

4) Recursively descend down in all directories listed in

   init-* core* drivers-* net-* libs-* and build all targets.

   - The values of the above variables are expanded in arch/$(ARCH)/Makefile.

   - The values of the above variables are expanded in arch/$(SRCARCH)/Makefile.

5) All object files are then linked and the resulting file vmlinux is

   located at the root of the obj tree.

   The very first objects linked are listed in head-y, assigned by

   arch/$(ARCH)/Makefile.

   arch/$(SRCARCH)/Makefile.

6) Finally, the architecture-specific part does any required post processing

   and builds the final bootimage.

   - This includes building boot records

		$(core-y), $(libs-y), $(drivers-y) and $(net-y).

	    The top level Makefile defines values for all generic directories,

	    and arch/$(ARCH)/Makefile only adds architecture-specific

	    and arch/$(SRCARCH)/Makefile only adds architecture-specific

	    directories.

	    Example::

	The actual goals are not standardized across architectures.

	It is common to locate any additional processing in a boot/

	directory below arch/$(ARCH)/.

	directory below arch/$(SRCARCH)/.

	Kbuild does not provide any smart way to support building a

	target specified in boot/. Therefore arch/$(ARCH)/Makefile shall

	target specified in boot/. Therefore arch/$(SRCARCH)/Makefile shall

	call make manually to build a target in boot/.

	The recommended approach is to include shortcuts in

	arch/$(ARCH)/Makefile, and use the full path when calling down

	into the arch/$(ARCH)/boot/Makefile.

	arch/$(SRCARCH)/Makefile, and use the full path when calling down

	into the arch/$(SRCARCH)/boot/Makefile.

	Example::

		#arch/x86/Makefile

		define archhelp

		  echo  '* bzImage      - Image (arch/$(ARCH)/boot/bzImage)'

		  echo  '* bzImage      - Compressed kernel image (arch/x86/boot/bzImage)'

		endif

	When make is executed without arguments, the first goal encountered

    objcopy

	Copy binary. Uses OBJCOPYFLAGS usually specified in

	arch/$(ARCH)/Makefile.

	arch/$(SRCARCH)/Makefile.

	OBJCOPYFLAGS_$@ may be used to set additional options.

    gzip

--------------------------------

	When the vmlinux image is built, the linker script

	arch/$(ARCH)/kernel/vmlinux.lds is used.

	arch/$(SRCARCH)/kernel/vmlinux.lds is used.

	The script is a preprocessed variant of the file vmlinux.lds.S

	located in the same directory.

	kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`.

		#arch/x86/kernel/Makefile

		extra-y := vmlinux.lds

		#Makefile

		export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)

	The assignment to extra-y is used to tell kbuild to build the

	target vmlinux.lds.

	The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the

	If an architecture uses a verbatim copy of a header from

	include/asm-generic then this is listed in the file

	arch/$(ARCH)/include/asm/Kbuild like this:

	arch/$(SRCARCH)/include/asm/Kbuild like this:

		Example::

	During the prepare phase of the build a wrapper include

	file is generated in the directory::

		arch/$(ARCH)/include/generated/asm

		arch/$(SRCARCH)/include/generated/asm

	When a header is exported where the architecture uses

	the generic header a similar wrapper is generated as part

	to define the minimum set of ASM headers that all architectures must have.

	This works like optional generic-y. If a mandatory header is missing

	in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate

	a wrapper of the asm-generic one.

	in arch/$(SRCARCH)/include/(uapi/)/asm, Kbuild will automatically

	generate a wrapper of the asm-generic one.

9 Kbuild Variables

==================

	    make ARCH=m68k ...

    SRCARCH

	This variable specifies the directory in arch/ to build.

	ARCH and SRCARCH may not necessarily match. A couple of arch

	directories are biarch, that is, a single `arch/*/` directory supports

	both 32-bit and 64-bit.

	For example, you can pass in ARCH=i386, ARCH=x86_64, or ARCH=x86.

	For all of them, SRCARCH=x86 because arch/x86/ supports	both i386 and

	x86_64.

    INSTALL_PATH

	This variable defines a place for the arch Makefiles to install

	      There are two notable exceptions to this rule: larger

	      subsystems have their own directory under include/, such as

	      include/scsi; and architecture specific headers are located

	      under arch/$(ARCH)/include/.

	      under arch/$(SRCARCH)/include/.

4.1 Kernel Includes

-------------------