Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

4 files changed, 1831 insertions, 0 deletions

diff --git a/Documentation/kbuild/00-INDEX b/Documentation/kbuild/00-INDEX
new file mode 100644
index 00000000000..11464428545
--- /dev/null
+++ b/Documentation/kbuild/00-INDEX
@@ -0,0 +1,8 @@
+00-INDEX
+    	- this file: info on the kernel build process
+kconfig-language.txt
+	- specification of Config Language, the language in Kconfig files
+makefiles.txt
+	- developer information for linux kernel makefiles
+modules.txt
+	- how to build modules and to install them
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
new file mode 100644
index 00000000000..ca1967f3642
--- /dev/null
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -0,0 +1,282 @@
+Introduction
+------------
+
+The configuration database is collection of configuration options
+organized in a tree structure:
+
+	+- Code maturity level options
+	|  +- Prompt for development and/or incomplete code/drivers
+	+- General setup
+	|  +- Networking support
+	|  +- System V IPC
+	|  +- BSD Process Accounting
+	|  +- Sysctl support
+	+- Loadable module support
+	|  +- Enable loadable module support
+	|     +- Set version information on all module symbols
+	|     +- Kernel module loader
+	+- ...
+
+Every entry has its own dependencies. These dependencies are used
+to determine the visibility of an entry. Any child entry is only
+visible if its parent entry is also visible.
+
+Menu entries
+------------
+
+Most entries define a config option, all other entries help to organize
+them. A single configuration option is defined like this:
+
+config MODVERSIONS
+	bool "Set version information on all module symbols"
+	depends MODULES
+	help
+	  Usually, modules have to be recompiled whenever you switch to a new
+	  kernel.  ...
+
+Every line starts with a key word and can be followed by multiple
+arguments.  "config" starts a new config entry. The following lines
+define attributes for this config option. Attributes can be the type of
+the config option, input prompt, dependencies, help text and default
+values. A config option can be defined multiple times with the same
+name, but every definition can have only a single input prompt and the
+type must not conflict.
+
+Menu attributes
+---------------
+
+A menu entry can have a number of attributes. Not all of them are
+applicable everywhere (see syntax).
+
+- type definition: "bool"/"tristate"/"string"/"hex"/"int"
+  Every config option must have a type. There are only two basic types:
+  tristate and string, the other types are based on these two. The type
+  definition optionally accepts an input prompt, so these two examples
+  are equivalent:
+
+	bool "Networking support"
+  and
+	bool
+	prompt "Networking support"
+
+- input prompt: "prompt" <prompt> ["if" <expr>]
+  Every menu entry can have at most one prompt, which is used to display
+  to the user. Optionally dependencies only for this prompt can be added
+  with "if".
+
+- default value: "default" <expr> ["if" <expr>]
+  A config option can have any number of default values. If multiple
+  default values are visible, only the first defined one is active.
+  Default values are not limited to the menu entry, where they are
+  defined, this means the default can be defined somewhere else or be
+  overridden by an earlier definition.
+  The default value is only assigned to the config symbol if no other
+  value was set by the user (via the input prompt above). If an input
+  prompt is visible the default value is presented to the user and can
+  be overridden by him.
+  Optionally dependencies only for this default value can be added with
+  "if".
+
+- dependencies: "depends on"/"requires" <expr>
+  This defines a dependency for this menu entry. If multiple
+  dependencies are defined they are connected with '&&'. Dependencies
+  are applied to all other options within this menu entry (which also
+  accept an "if" expression), so these two examples are equivalent:
+
+	bool "foo" if BAR
+	default y if BAR
+  and
+	depends on BAR
+	bool "foo"
+	default y
+
+- reverse dependencies: "select" <symbol> ["if" <expr>]
+  While normal dependencies reduce the upper limit of a symbol (see
+  below), reverse dependencies can be used to force a lower limit of
+  another symbol. The value of the current menu symbol is used as the
+  minimal value <symbol> can be set to. If <symbol> is selected multiple
+  times, the limit is set to the largest selection.
+  Reverse dependencies can only be used with boolean or tristate
+  symbols.
+
+- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
+  This allows to limit the range of possible input values for int
+  and hex symbols. The user can only input a value which is larger than
+  or equal to the first symbol and smaller than or equal to the second
+  symbol.
+
+- help text: "help" or "---help---"
+  This defines a help text. The end of the help text is determined by
+  the indentation level, this means it ends at the first line which has
+  a smaller indentation than the first line of the help text.
+  "---help---" and "help" do not differ in behaviour, "---help---" is
+  used to help visually seperate configuration logic from help within
+  the file as an aid to developers.
+
+
+Menu dependencies
+-----------------
+
+Dependencies define the visibility of a menu entry and can also reduce
+the input range of tristate symbols. The tristate logic used in the
+expressions uses one more state than normal boolean logic to express the
+module state. Dependency expressions have the following syntax:
+
+<expr> ::= <symbol>                             (1)
+           <symbol> '=' <symbol>                (2)
+           <symbol> '!=' <symbol>               (3)
+           '(' <expr> ')'                       (4)
+           '!' <expr>                           (5)
+           <expr> '&&' <expr>                   (6)
+           <expr> '||' <expr>                   (7)
+
+Expressions are listed in decreasing order of precedence. 
+
+(1) Convert the symbol into an expression. Boolean and tristate symbols
+    are simply converted into the respective expression values. All
+    other symbol types result in 'n'.
+(2) If the values of both symbols are equal, it returns 'y',
+    otherwise 'n'.
+(3) If the values of both symbols are equal, it returns 'n',
+    otherwise 'y'.
+(4) Returns the value of the expression. Used to override precedence.
+(5) Returns the result of (2-/expr/).
+(6) Returns the result of min(/expr/, /expr/).
+(7) Returns the result of max(/expr/, /expr/).
+
+An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
+respectively for calculations). A menu entry becomes visible when it's
+expression evaluates to 'm' or 'y'.
+
+There are two types of symbols: constant and nonconstant symbols.
+Nonconstant symbols are the most common ones and are defined with the
+'config' statement. Nonconstant symbols consist entirely of alphanumeric
+characters or underscores.
+Constant symbols are only part of expressions. Constant symbols are
+always surrounded by single or double quotes. Within the quote any
+other character is allowed and the quotes can be escaped using '\'.
+
+Menu structure
+--------------
+
+The position of a menu entry in the tree is determined in two ways. First
+it can be specified explicitly:
+
+menu "Network device support"
+	depends NET
+
+config NETDEVICES
+	...
+
+endmenu
+
+All entries within the "menu" ... "endmenu" block become a submenu of
+"Network device support". All subentries inherit the dependencies from
+the menu entry, e.g. this means the dependency "NET" is added to the
+dependency list of the config option NETDEVICES.
+
+The other way to generate the menu structure is done by analyzing the
+dependencies. If a menu entry somehow depends on the previous entry, it
+can be made a submenu of it. First, the previous (parent) symbol must
+be part of the dependency list and then one of these two conditions
+must be true:
+- the child entry must become invisible, if the parent is set to 'n'
+- the child entry must only be visible, if the parent is visible
+
+config MODULES
+	bool "Enable loadable module support"
+
+config MODVERSIONS
+	bool "Set version information on all module symbols"
+	depends MODULES
+
+comment "module support disabled"
+	depends !MODULES
+
+MODVERSIONS directly depends on MODULES, this means it's only visible if
+MODULES is different from 'n'. The comment on the other hand is always
+visible when MODULES is visible (the (empty) dependency of MODULES is
+also part of the comment dependencies).
+
+
+Kconfig syntax
+--------------
+
+The configuration file describes a series of menu entries, where every
+line starts with a keyword (except help texts). The following keywords
+end a menu entry:
+- config
+- menuconfig
+- choice/endchoice
+- comment
+- menu/endmenu
+- if/endif
+- source
+The first five also start the definition of a menu entry.
+
+config:
+
+	"config" <symbol>
+	<config options>
+
+This defines a config symbol <symbol> and accepts any of above
+attributes as options.
+
+menuconfig:
+	"menuconfig" <symbol>
+	<config options>
+
+This is similiar to the simple config entry above, but it also gives a
+hint to front ends, that all suboptions should be displayed as a
+separate list of options.
+
+choices:
+
+	"choice"
+	<choice options>
+	<choice block>
+	"endchoice"
+
+This defines a choice group and accepts any of above attributes as
+options. A choice can only be of type bool or tristate, while a boolean
+choice only allows a single config entry to be selected, a tristate
+choice also allows any number of config entries to be set to 'm'. This
+can be used if multiple drivers for a single hardware exists and only a
+single driver can be compiled/loaded into the kernel, but all drivers
+can be compiled as modules.
+A choice accepts another option "optional", which allows to set the
+choice to 'n' and no entry needs to be selected.
+
+comment:
+
+	"comment" <prompt>
+	<comment options>
+
+This defines a comment which is displayed to the user during the
+configuration process and is also echoed to the output files. The only
+possible options are dependencies.
+
+menu:
+
+	"menu" <prompt>
+	<menu options>
+	<menu block>
+	"endmenu"
+
+This defines a menu block, see "Menu structure" above for more
+information. The only possible options are dependencies.
+
+if:
+
+	"if" <expr>
+	<if block>
+	"endif"
+
+This defines an if block. The dependency expression <expr> is appended
+to all enclosed menu entries.
+
+source:
+
+	"source" <prompt>
+
+This reads the specified configuration file. This file is always parsed.
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
new file mode 100644
index 00000000000..2616a58a5a4
--- /dev/null
+++ b/Documentation/kbuild/makefiles.txt
@@ -0,0 +1,1122 @@
+Linux Kernel Makefiles
+
+This document describes the Linux kernel Makefiles.
+
+=== Table of Contents
+
+	=== 1 Overview
+	=== 2 Who does what
+	=== 3 The kbuild files
+	   --- 3.1 Goal definitions
+	   --- 3.2 Built-in object goals - obj-y
+	   --- 3.3 Loadable module goals - obj-m
+	   --- 3.4 Objects which export symbols
+	   --- 3.5 Library file goals - lib-y
+	   --- 3.6 Descending down in directories
+	   --- 3.7 Compilation flags
+	   --- 3.8 Command line dependency
+	   --- 3.9 Dependency tracking
+	   --- 3.10 Special Rules
+
+	=== 4 Host Program support
+	   --- 4.1 Simple Host Program
+	   --- 4.2 Composite Host Programs
+	   --- 4.3 Defining shared libraries  
+	   --- 4.4 Using C++ for host programs
+	   --- 4.5 Controlling compiler options for host programs
+	   --- 4.6 When host programs are actually built
+	   --- 4.7 Using hostprogs-$(CONFIG_FOO)
+
+	=== 5 Kbuild clean infrastructure
+
+	=== 6 Architecture Makefiles
+	   --- 6.1 Set variables to tweak the build to the architecture
+	   --- 6.2 Add prerequisites to prepare:
+	   --- 6.3 List directories to visit when descending
+	   --- 6.4 Architecture specific boot images
+	   --- 6.5 Building non-kbuild targets
+	   --- 6.6 Commands useful for building a boot image
+	   --- 6.7 Custom kbuild commands
+	   --- 6.8 Preprocessing linker scripts
+	   --- 6.9 $(CC) support functions
+
+	=== 7 Kbuild Variables
+	=== 8 Makefile language
+	=== 9 Credits
+	=== 10 TODO
+
+=== 1 Overview
+
+The Makefiles have five parts:
+
+	Makefile		the top Makefile.
+	.config			the kernel configuration file.
+	arch/$(ARCH)/Makefile	the arch Makefile.
+	scripts/Makefile.*	common rules etc. for all kbuild Makefiles.
+	kbuild Makefiles	there are about 500 of these.
+
+The top Makefile reads the .config file, which comes from the kernel
+configuration process.
+
+The top Makefile is responsible for building two major products: vmlinux
+(the resident kernel image) and modules (any module files).
+It builds these goals by recursively descending into the subdirectories of
+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
+architecture-specific information to the top Makefile.
+
+Each subdirectory has a kbuild Makefile which carries out the commands
+passed down from above. The kbuild Makefile uses information from the
+.config file to construct various file lists used by kbuild to build 
+any built-in or modular targets.
+
+scripts/Makefile.* contains all the definitions/rules etc. that
+are used to build the kernel based on the kbuild makefiles.
+
+
+=== 2 Who does what
+
+People have four different relationships with the kernel Makefiles.
+
+*Users* are people who build kernels.  These people type commands such as
+"make menuconfig" or "make".  They usually do not read or edit
+any kernel Makefiles (or any other source files).
+
+*Normal developers* are people who work on features such as device
+drivers, file systems, and network protocols.  These people need to
+maintain the kbuild Makefiles for the subsystem that they are
+working on.  In order to do this effectively, they need some overall
+knowledge about the kernel Makefiles, plus detailed knowledge about the
+public interface for kbuild.
+
+*Arch developers* are people who work on an entire architecture, such
+as sparc or ia64.  Arch developers need to know about the arch Makefile
+as well as kbuild Makefiles.
+
+*Kbuild developers* are people who work on the kernel build system itself.
+These people need to know about all aspects of the kernel Makefiles.
+
+This document is aimed towards normal developers and arch developers.
+
+
+=== 3 The kbuild files
+
+Most Makefiles within the kernel are kbuild Makefiles that use the
+kbuild infrastructure. This chapter introduce the syntax used in the
+kbuild makefiles.
+The preferred name for the kbuild files is 'Kbuild' but 'Makefile' will
+continue to be supported. All new developmen is expected to use the
+Kbuild filename.
+
+Section 3.1 "Goal definitions" is a quick intro, further chapters provide
+more details, with real examples.
+
+--- 3.1 Goal definitions
+
+	Goal definitions are the main part (heart) of the kbuild Makefile.
+	These lines define the files to be built, any special compilation
+	options, and any subdirectories to be entered recursively.
+
+	The most simple kbuild makefile contains one line:
+
+	Example:
+		obj-y += foo.o
+
+	This tell kbuild that there is one object in that directory named
+	foo.o. foo.o will be built from foo.c or foo.S.
+
+	If foo.o shall be built as a module, the variable obj-m is used.
+	Therefore the following pattern is often used:
+
+	Example:
+		obj-$(CONFIG_FOO) += foo.o
+
+	$(CONFIG_FOO) evaluates to either y (for built-in) or m (for module).
+	If CONFIG_FOO is neither y nor m, then the file will not be compiled
+	nor linked.
+
+--- 3.2 Built-in object goals - obj-y
+
+	The kbuild Makefile specifies object files for vmlinux
+	in the lists $(obj-y).  These lists depend on the kernel
+	configuration.
+
+	Kbuild compiles all the $(obj-y) files.  It then calls
+	"$(LD) -r" to merge these files into one built-in.o file.
+	built-in.o is later linked into vmlinux by the parent Makefile.
+
+	The order of files in $(obj-y) is significant.  Duplicates in
+	the lists are allowed: the first instance will be linked into
+	built-in.o and succeeding instances will be ignored.
+
+	Link order is significant, because certain functions
+	(module_init() / __initcall) will be called during boot in the
+	order they appear. So keep in mind that changing the link
+	order may e.g.  change the order in which your SCSI
+	controllers are detected, and thus you disks are renumbered.
+
+	Example:
+		#drivers/isdn/i4l/Makefile
+		# Makefile for the kernel ISDN subsystem and device drivers.
+		# Each configuration option enables a list of files.
+		obj-$(CONFIG_ISDN)             += isdn.o
+		obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
+
+--- 3.3 Loadable module goals - obj-m
+
+	$(obj-m) specify object files which are built as loadable
+	kernel modules.
+
+	A module may be built from one source file or several source
+	files. In the case of one source file, the kbuild makefile
+	simply adds the file to $(obj-m).
+
+	Example:
+		#drivers/isdn/i4l/Makefile
+		obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
+
+	Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm'
+
+	If a kernel module is built from several source files, you specify
+	that you want to build a module in the same way as above.
+
+	Kbuild needs to know which the parts that you want to build your
+	module from, so you have to tell it by setting an
+	$(<module_name>-objs) variable.
+
+	Example:
+		#drivers/isdn/i4l/Makefile
+		obj-$(CONFIG_ISDN) += isdn.o
+		isdn-objs := isdn_net_lib.o isdn_v110.o isdn_common.o
+
+	In this example, the module name will be isdn.o. Kbuild will
+	compile the objects listed in $(isdn-objs) and then run
+	"$(LD) -r" on the list of these files to generate isdn.o.
+
+	Kbuild recognises objects used for composite objects by the suffix
+	-objs, and the suffix -y. This allows the Makefiles to use
+	the value of a CONFIG_ symbol to determine if an object is part
+	of a composite object.
+
+	Example:
+		#fs/ext2/Makefile
+	        obj-$(CONFIG_EXT2_FS)        += ext2.o
+	 	ext2-y                       := balloc.o bitmap.o
+	        ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
+	
+	In this example xattr.o is only part of the composite object
+	ext2.o, if $(CONFIG_EXT2_FS_XATTR) evaluates to 'y'.
+
+	Note: Of course, when you are building objects into the kernel,
+	the syntax above will also work. So, if you have CONFIG_EXT2_FS=y,
+	kbuild will build an ext2.o file for you out of the individual
+	parts and then link this into built-in.o, as you would expect.
+
+--- 3.4 Objects which export symbols
+
+	No special notation is required in the makefiles for
+	modules exporting symbols.
+
+--- 3.5 Library file goals - lib-y
+
+	Objects listed with obj-* are used for modules or
+	combined in a built-in.o for that specific directory.
+	There is also the possibility to list objects that will
+	be included in a library, lib.a.
+	All objects listed with lib-y are combined in a single
+	library for that directory.
+	Objects that are listed in obj-y and additional listed in
+	lib-y will not be included in the library, since they will anyway
+	be accessible.
+	For consistency objects listed in lib-m will be included in lib.a. 
+
+	Note that the same kbuild makefile may list files to be built-in
+	and to be part of a library. Therefore the same directory
+	may contain both a built-in.o and a lib.a file.
+
+	Example:
+		#arch/i386/lib/Makefile
+		lib-y    := checksum.o delay.o
+
+	This will create a library lib.a based on checksum.o and delay.o.
+	For kbuild to actually recognize that there is a lib.a being build
+	the directory shall be listed in libs-y.
+	See also "6.3 List directories to visit when descending".
+ 
+	Usage of lib-y is normally restricted to lib/ and arch/*/lib.
+
+--- 3.6 Descending down in directories
+
+	A Makefile is only responsible for building objects in its own
+	directory. Files in subdirectories should be taken care of by
+	Makefiles in these subdirs. The build system will automatically
+	invoke make recursively in subdirectories, provided you let it know of
+	them.
+
+	To do so obj-y and obj-m are used.
+	ext2 lives in a separate directory, and the Makefile present in fs/
+	tells kbuild to descend down using the following assignment.
+
+	Example:
+		#fs/Makefile
+		obj-$(CONFIG_EXT2_FS) += ext2/
+
+	If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular)
+	the corresponding obj- variable will be set, and kbuild will descend
+	down in the ext2 directory.
+	Kbuild only uses this information to decide that it needs to visit
+	the directory, it is the Makefile in the subdirectory that
+	specifies what is modules and what is built-in.
+
+	It is good practice to use a CONFIG_ variable when assigning directory
+	names. This allows kbuild to totally skip the directory if the
+	corresponding CONFIG_ option is neither 'y' nor 'm'.
+
+--- 3.7 Compilation flags
+
+    EXTRA_CFLAGS, EXTRA_AFLAGS, EXTRA_LDFLAGS, EXTRA_ARFLAGS
+
+	All the EXTRA_ variables apply only to the kbuild makefile
+	where they are assigned. The EXTRA_ variables apply to all
+	commands executed in the kbuild makefile.
+
+	$(EXTRA_CFLAGS) specifies options for compiling C files with
+	$(CC).
+
+	Example:
+		# drivers/sound/emu10k1/Makefile
+		EXTRA_CFLAGS += -I$(obj)
+		ifdef DEBUG
+		    EXTRA_CFLAGS += -DEMU10K1_DEBUG
+		endif
+
+
+	This variable is necessary because the top Makefile owns the
+	variable $(CFLAGS) and uses it for compilation flags for the
+	entire tree.
+
+	$(EXTRA_AFLAGS) is a similar string for per-directory options
+	when compiling assembly language source.
+
+	Example:
+		#arch/x86_64/kernel/Makefile
+		EXTRA_AFLAGS := -traditional
+
+
+	$(EXTRA_LDFLAGS) and $(EXTRA_ARFLAGS) are similar strings for
+	per-directory options to $(LD) and $(AR).
+
+	Example:
+		#arch/m68k/fpsp040/Makefile
+		EXTRA_LDFLAGS := -x
+
+    CFLAGS_$@, AFLAGS_$@
+
+	CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
+	kbuild makefile.
+
+	$(CFLAGS_$@) specifies per-file options for $(CC).  The $@
+	part has a literal value which specifies the file that it is for.
+
+	Example:
+		# drivers/scsi/Makefile
+		CFLAGS_aha152x.o =   -DAHA152X_STAT -DAUTOCONF
+		CFLAGS_gdth.o    = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \
+				     -DGDTH_STATISTICS
+		CFLAGS_seagate.o =   -DARBITRATE -DPARITY -DSEAGATE_USE_ASM
+
+	These three lines specify compilation flags for aha152x.o,
+	gdth.o, and seagate.o
+
+	$(AFLAGS_$@) is a similar feature for source files in assembly
+	languages.
+
+	Example:
+		# arch/arm/kernel/Makefile
+		AFLAGS_head-armv.o := -DTEXTADDR=$(TEXTADDR) -traditional
+		AFLAGS_head-armo.o := -DTEXTADDR=$(TEXTADDR) -traditional
+
+--- 3.9 Dependency tracking
+
+	Kbuild tracks dependencies on the following:
+	1) All prerequisite files (both *.c and *.h)
+	2) CONFIG_ options used in all prerequisite files
+	3) Command-line used to compile target
+
+	Thus, if you change an option to $(CC) all affected files will
+	be re-compiled.
+
+--- 3.10 Special Rules
+
+	Special rules are used when the kbuild infrastructure does
+	not provide the required support. A typical example is
+	header files generated during the build process.
+	Another example is the architecture specific Makefiles which
+	needs special rules to prepare boot images etc.
+
+	Special rules are written as normal Make rules.
+	Kbuild is not executing in the directory where the Makefile is
+	located, so all special rules shall provide a relative
+	path to prerequisite files and target files.
+
+	Two variables are used when defining special rules:
+
+    $(src)
+	$(src) is a relative path which points to the directory
+	where the Makefile is located. Always use $(src) when
+	referring to files located in the src tree.
+
+    $(obj)
+	$(obj) is a relative path which points to the directory
+	where the target is saved. Always use $(obj) when
+	referring to generated files.
+
+	Example:
+		#drivers/scsi/Makefile
+		$(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl
+			$(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl
+
+	This is a special rule, following the normal syntax
+	required by make.
+	The target file depends on two prerequisite files. References
+	to the target file are prefixed with $(obj), references
+	to prerequisites are referenced with $(src) (because they are not
+	generated files).
+
+
+=== 4 Host Program support
+
+Kbuild supports building executables on the host for use during the
+compilation stage.
+Two steps are required in order to use a host executable.
+
+The first step is to tell kbuild that a host program exists. This is
+done utilising the variable hostprogs-y.
+
+The second step is to add an explicit dependency to the executable.
+This can be done in two ways. Either add the dependency in a rule, 
+or utilise the variable $(always).
+Both possibilities are described in the following.
+
+--- 4.1 Simple Host Program
+
+	In some cases there is a need to compile and run a program on the
+	computer where the build is running.
+	The following line tells kbuild that the program bin2hex shall be
+	built on the build host.
+
+	Example:
+		hostprogs-y := bin2hex
+
+	Kbuild assumes in the above example that bin2hex is made from a single
+	c-source file named bin2hex.c located in the same directory as
+	the Makefile.
+  
+--- 4.2 Composite Host Programs
+
+	Host programs can be made up based on composite objects.
+	The syntax used to define composite objects for host programs is
+	similar to the syntax used for kernel objects.
+	$(<executeable>-objs) list all objects used to link the final
+	executable.
+
+	Example:
+		#scripts/lxdialog/Makefile
+		hostprogs-y   := lxdialog  
+		lxdialog-objs := checklist.o lxdialog.o
+
+	Objects with extension .o are compiled from the corresponding .c
+	files. In the above example checklist.c is compiled to checklist.o
+	and lxdialog.c is compiled to lxdialog.o.
+	Finally the two .o files are linked to the executable, lxdialog.
+	Note: The syntax <executable>-y is not permitted for host-programs.
+
+--- 4.3 Defining shared libraries  
+  
+	Objects with extension .so are considered shared libraries, and
+	will be compiled as position independent objects.
+	Kbuild provides support for shared libraries, but the usage
+	shall be restricted.
+	In the following example the libkconfig.so shared library is used
+	to link the executable conf.
+
+	Example:
+		#scripts/kconfig/Makefile
+		hostprogs-y     := conf
+		conf-objs       := conf.o libkconfig.so
+		libkconfig-objs := expr.o type.o
+  
+	Shared libraries always require a corresponding -objs line, and
+	in the example above the shared library libkconfig is composed by
+	the two objects expr.o and type.o.
+	expr.o and type.o will be built as position independent code and
+	linked as a shared library libkconfig.so. C++ is not supported for
+	shared libraries.
+
+--- 4.4 Using C++ for host programs
+
+	kbuild offers support for host programs written in C++. This was
+	introduced solely to support kconfig, and is not recommended
+	for general use.
+
+	Example:
+		#scripts/kconfig/Makefile
+		hostprogs-y   := qconf
+		qconf-cxxobjs := qconf.o
+
+	In the example above the executable is composed of the C++ file
+	qconf.cc - identified by $(qconf-cxxobjs).
+	
+	If qconf is composed by a mixture of .c and .cc files, then an
+	additional line can be used to identify this.
+
+	Example:
+		#scripts/kconfig/Makefile
+		hostprogs-y   := qconf
+		qconf-cxxobjs := qconf.o
+		qconf-objs    := check.o
+	
+--- 4.5 Controlling compiler options for host programs
+
+	When compiling host programs, it is possible to set specific flags.
+	The programs will always be compiled utilising $(HOSTCC) passed
+	the options specified in $(HOSTCFLAGS).
+	To set flags that will take effect for all host programs created
+	in that Makefile use the variable HOST_EXTRACFLAGS.
+
+	Example:
+		#scripts/lxdialog/Makefile
+		HOST_EXTRACFLAGS += -I/usr/include/ncurses
+  
+	To set specific flags for a single file the following construction
+	is used:
+
+	Example:
+		#arch/ppc64/boot/Makefile
+		HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE)
+  
+	It is also possible to specify additional options to the linker.
+  
+	Example:
+		#scripts/kconfig/Makefile
+		HOSTLOADLIBES_qconf := -L$(QTDIR)/lib
+
+	When linking qconf it will be passed the extra option "-L$(QTDIR)/lib".
+ 
+--- 4.6 When host programs are actually built
+
+	Kbuild will only build host-programs when they are referenced
+	as a prerequisite.
+	This is possible in two ways:
+
+	(1) List the prerequisite explicitly in a special rule.
+
+	Example:
+		#drivers/pci/Makefile
+		hostprogs-y := gen-devlist
+		$(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist
+			( cd $(obj); ./gen-devlist ) < $<
+
+	The target $(obj)/devlist.h will not be built before 
+	$(obj)/gen-devlist is updated. Note that references to
+	the host programs in special rules must be prefixed with $(obj).
+
+	(2) Use $(always)
+	When there is no suitable special rule, and the host program
+	shall be built when a makefile is entered, the $(always)
+	variable shall be used.
+
+	Example:
+		#scripts/lxdialog/Makefile
+		hostprogs-y   := lxdialog
+		always        := $(hostprogs-y)
+
+	This will tell kbuild to build lxdialog even if not referenced in
+	any rule.
+
+--- 4.7 Using hostprogs-$(CONFIG_FOO)
+
+	A typcal pattern in a Kbuild file lok like this:
+
+	Example:
+		#scripts/Makefile
+		hostprogs-$(CONFIG_KALLSYMS) += kallsyms
+
+	Kbuild knows about both 'y' for built-in and 'm' for module.
+	So if a config symbol evaluate to 'm', kbuild will still build
+	the binary. In other words Kbuild handle hostprogs-m exactly
+	like hostprogs-y. But only hostprogs-y is recommend used
+	when no CONFIG symbol are involved.
+
+=== 5 Kbuild clean infrastructure
+
+"make clean" deletes most generated files in the src tree where the kernel
+is compiled. This includes generated files such as host programs.
+Kbuild knows targets listed in $(hostprogs-y), $(hostprogs-m), $(always),
+$(extra-y) and $(targets). They are all deleted during "make clean".
+Files matching the patterns "*.[oas]", "*.ko", plus some additional files
+generated by kbuild are deleted all over the kernel src tree when
+"make clean" is executed.
+
+Additional files can be specified in kbuild makefiles by use of $(clean-files).
+
+	Example:
+		#drivers/pci/Makefile
+		clean-files := devlist.h classlist.h
+
+When executing "make clean", the two files "devlist.h classlist.h" will
+be deleted. Kbuild will assume files to be in same relative directory as the
+Makefile except if an absolute path is specified (path starting with '/').
+
+To delete a directory hirachy use:
+	Example:
+		#scripts/package/Makefile
+		clean-dirs := $(objtree)/debian/
+
+This will delete the directory debian, including all subdirectories.
+Kbuild will assume the directories to be in the same relative path as the
+Makefile if no absolute path is specified (path does not start with '/').
+
+Usually kbuild descends down in subdirectories due to "obj-* := dir/",
+but in the architecture makefiles where the kbuild infrastructure
+is not sufficient this sometimes needs to be explicit.
+
+	Example:
+		#arch/i386/boot/Makefile
+		subdir- := compressed/
+
+The above assignment instructs kbuild to descend down in the
+directory compressed/ when "make clean" is executed.
+
+To support the clean infrastructure in the Makefiles that builds the
+final bootimage there is an optional target named archclean:
+
+	Example:
+		#arch/i386/Makefile
+		archclean:
+			$(Q)$(MAKE) $(clean)=arch/i386/boot
+
+When "make clean" is executed, make will descend down in arch/i386/boot,
+and clean as usual. The Makefile located in arch/i386/boot/ may use
+the subdir- trick to descend further down.
+
+Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is
+included in the top level makefile, and the kbuild infrastructure
+is not operational at that point.
+
+Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will
+be visited during "make clean".
+
+=== 6 Architecture Makefiles
+
+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 the
+arch/$(ARCH)/Makefile contains what is required to set-up kbuild
+to the said architecture.
+To do so arch/$(ARCH)/Makefile sets a number of variables, and defines
+a few targets.
+
+When kbuild executes the following steps are followed (roughly):
+1) Configuration of the kernel => produced .config
+2) Store kernel version in include/linux/version.h
+3) Symlink include/asm to include/asm-$(ARCH)
+4) Updating all other prerequisites to the target prepare:
+   - Additional prerequisites are specified in arch/$(ARCH)/Makefile
+5) Recursively descend down in all directories listed in
+   init-* core* drivers-* net-* libs-* and build all targets.
+   - The value of the above variables are extended in arch/$(ARCH)/Makefile.
+6) All object files are then linked and the resulting file vmlinux is 
+   located at the root of the src tree.
+   The very first objects linked are listed in head-y, assigned by
+   arch/$(ARCH)/Makefile.
+7) Finally the architecture specific part does any required post processing
+   and builds the final bootimage.
+   - This includes building boot records
+   - Preparing initrd images and the like
+
+
+--- 6.1 Set variables to tweak the build to the architecture
+
+    LDFLAGS		Generic $(LD) options
+
+	Flags used for all invocations of the linker.
+	Often specifying the emulation is sufficient.
+
+	Example:
+		#arch/s390/Makefile
+		LDFLAGS         := -m elf_s390
+	Note: EXTRA_LDFLAGS and LDFLAGS_$@ can be used to further customise
+	the flags used. See chapter 7.
+	
+    LDFLAGS_MODULE	Options for $(LD) when linking modules
+
+	LDFLAGS_MODULE is used to set specific flags for $(LD) when
+	linking the .ko files used for modules.
+	Default is "-r", for relocatable output.
+
+    LDFLAGS_vmlinux	Options for $(LD) when linking vmlinux
+
+	LDFLAGS_vmlinux is used to specify additional flags to pass to
+	the linker when linking the final vmlinux.
+	LDFLAGS_vmlinux uses the LDFLAGS_$@ support.
+
+	Example:
+		#arch/i386/Makefile
+		LDFLAGS_vmlinux := -e stext
+
+    OBJCOPYFLAGS	objcopy flags
+
+	When $(call if_changed,objcopy) is used to translate a .o file,
+	then the flags specified in OBJCOPYFLAGS will be used.
+	$(call if_changed,objcopy) is often used to generate raw binaries on
+	vmlinux.
+
+	Example:
+		#arch/s390/Makefile
+		OBJCOPYFLAGS := -O binary
+
+		#arch/s390/boot/Makefile
+		$(obj)/image: vmlinux FORCE
+			$(call if_changed,objcopy)
+
+	In this example the binary $(obj)/image is a binary version of
+	vmlinux. The usage of $(call if_changed,xxx) will be described later.
+
+    AFLAGS		$(AS) assembler flags
+
+	Default value - see top level Makefile
+	Append or modify as required per architecture.