File-copy from v4.4.100
This is the result of 'cp' from a linux-stable tree with the 'v4.4.100'
tag checked out (commit 26d6298789e695c9f627ce49a7bbd2286405798a) on
git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Please refer to that tree for all history prior to this point.
Change-Id: I8a9ee2aea93cd29c52c847d0ce33091a73ae6afe
diff --git a/Documentation/kbuild/00-INDEX b/Documentation/kbuild/00-INDEX
new file mode 100644
index 0000000..8c5e6aa
--- /dev/null
+++ b/Documentation/kbuild/00-INDEX
@@ -0,0 +1,14 @@
+00-INDEX
+ - this file: info on the kernel build process
+headers_install.txt
+ - how to export Linux headers for use by userspace
+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
+modules.txt
+ - how to build modules and to install them
diff --git a/Documentation/kbuild/Kconfig.recursion-issue-01 b/Documentation/kbuild/Kconfig.recursion-issue-01
new file mode 100644
index 0000000..e8877db
--- /dev/null
+++ b/Documentation/kbuild/Kconfig.recursion-issue-01
@@ -0,0 +1,57 @@
+# Simple Kconfig recursive issue
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#
+# Test with:
+#
+# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
+#
+# This Kconfig file has a simple recursive dependency issue. In order to
+# understand why this recursive dependency issue occurs lets consider what
+# Kconfig needs to address. We iterate over what Kconfig needs to address
+# by stepping through the questions it needs to address sequentially.
+#
+# * What values are possible for CORE?
+#
+# CORE_BELL_A_ADVANCED selects CORE, which means that it influences the values
+# that are possible for CORE. So for example if CORE_BELL_A_ADVANCED is 'y',
+# CORE must be 'y' too.
+#
+# * What influences CORE_BELL_A_ADVANCED ?
+#
+# As the name implies CORE_BELL_A_ADVANCED is an advanced feature of
+# CORE_BELL_A so naturally it depends on CORE_BELL_A. So if CORE_BELL_A is 'y'
+# we know CORE_BELL_A_ADVANCED can be 'y' too.
+#
+# * What influences CORE_BELL_A ?
+#
+# CORE_BELL_A depends on CORE, so CORE influences CORE_BELL_A.
+#
+# But that is a problem, because this means that in order to determine
+# what values are possible for CORE we ended up needing to address questions
+# regarding possible values of CORE itself again. Answering the original
+# question of what are the possible values of CORE would make the kconfig
+# tools run in a loop. When this happens Kconfig exits and complains about
+# the "recursive dependency detected" error.
+#
+# Reading the Documentation/kbuild/Kconfig.recursion-issue-01 file it may be
+# obvious that an easy to solution to this problem should just be the removal
+# of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already
+# since CORE_BELL_A depends on CORE. Recursive dependency issues are not always
+# so trivial to resolve, we provide another example below of practical
+# implications of this recursive issue where the solution is perhaps not so
+# easy to understand. Note that matching semantics on the dependency on
+# CORE also consist of a solution to this recursive problem.
+
+mainmenu "Simple example to demo kconfig recursive dependency issue"
+
+config CORE
+ tristate
+
+config CORE_BELL_A
+ tristate
+ depends on CORE
+
+config CORE_BELL_A_ADVANCED
+ tristate
+ depends on CORE_BELL_A
+ select CORE
diff --git a/Documentation/kbuild/Kconfig.recursion-issue-02 b/Documentation/kbuild/Kconfig.recursion-issue-02
new file mode 100644
index 0000000..b9fd56c
--- /dev/null
+++ b/Documentation/kbuild/Kconfig.recursion-issue-02
@@ -0,0 +1,63 @@
+# Cumulative Kconfig recursive issue
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#
+# Test with:
+#
+# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
+#
+# The recursive limitations with Kconfig has some non intuitive implications on
+# kconfig sematics which are documented here. One known practical implication
+# of the recursive limitation is that drivers cannot negate features from other
+# drivers if they share a common core requirement and use disjoint semantics to
+# annotate those requirements, ie, some drivers use "depends on" while others
+# use "select". For instance it means if a driver A and driver B share the same
+# core requirement, and one uses "select" while the other uses "depends on" to
+# annotate this, all features that driver A selects cannot now be negated by
+# driver B.
+#
+# A perhaps not so obvious implication of this is that, if semantics on these
+# core requirements are not carefully synced, as drivers evolve features
+# they select or depend on end up becoming shared requirements which cannot be
+# negated by other drivers.
+#
+# The example provided in Documentation/kbuild/Kconfig.recursion-issue-02
+# describes a simple driver core layout of example features a kernel might
+# have. Let's assume we have some CORE functionality, then the kernel has a
+# series of bells and whistles it desires to implement, its not so advanced so
+# it only supports bells at this time: CORE_BELL_A and CORE_BELL_B. If
+# CORE_BELL_A has some advanced feature CORE_BELL_A_ADVANCED which selects
+# CORE_BELL_A then CORE_BELL_A ends up becoming a common BELL feature which
+# other bells in the system cannot negate. The reason for this issue is
+# due to the disjoint use of semantics on expressing each bell's relationship
+# with CORE, one uses "depends on" while the other uses "select". Another
+# more important reason is that kconfig does not check for dependencies listed
+# under 'select' for a symbol, when such symbols are selected kconfig them
+# as mandatory required symbols. For more details on the heavy handed nature
+# of select refer to Documentation/kbuild/Kconfig.select-break
+#
+# To fix this the "depends on CORE" must be changed to "select CORE", or the
+# "select CORE" must be changed to "depends on CORE".
+#
+# For an example real world scenario issue refer to the attempt to remove
+# "select FW_LOADER" [0], in the end the simple alternative solution to this
+# problem consisted on matching semantics with newly introduced features.
+#
+# [0] http://lkml.kernel.org/r/1432241149-8762-1-git-send-email-mcgrof@do-not-panic.com
+
+mainmenu "Simple example to demo cumulative kconfig recursive dependency implication"
+
+config CORE
+ tristate
+
+config CORE_BELL_A
+ tristate
+ depends on CORE
+
+config CORE_BELL_A_ADVANCED
+ tristate
+ select CORE_BELL_A
+
+config CORE_BELL_B
+ tristate
+ depends on !CORE_BELL_A
+ select CORE
diff --git a/Documentation/kbuild/Kconfig.select-break b/Documentation/kbuild/Kconfig.select-break
new file mode 100644
index 0000000..365ceb3
--- /dev/null
+++ b/Documentation/kbuild/Kconfig.select-break
@@ -0,0 +1,33 @@
+# Select broken dependency issue
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#
+# Test with:
+#
+# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.select-break menuconfig
+#
+# kconfig will not complain and enable this layout for configuration. This is
+# currently a feature of kconfig, given select was designed to be heavy handed.
+# Kconfig currently does not check the list of symbols listed on a symbol's
+# "select" list, this is done on purpose to help load a set of known required
+# symbols. Because of this use of select should be used with caution. An
+# example of this issue is below.
+#
+# The option B and C are clearly contradicting with respect to A.
+# However, when A is set, C can be set as well because Kconfig does not
+# visit the dependencies of the select target (in this case B). And since
+# Kconfig does not visit the dependencies, it breaks the dependencies of B
+# (!A).
+
+mainmenu "Simple example to demo kconfig select broken dependency issue"
+
+config A
+ bool "CONFIG A"
+
+config B
+ bool "CONFIG B"
+ depends on !A
+
+config C
+ bool "CONFIG C"
+ depends on A
+ select B
diff --git a/Documentation/kbuild/headers_install.txt b/Documentation/kbuild/headers_install.txt
new file mode 100644
index 0000000..f0153ad
--- /dev/null
+++ b/Documentation/kbuild/headers_install.txt
@@ -0,0 +1,50 @@
+Exporting kernel headers for use by userspace
+=============================================
+
+The "make headers_install" command exports the kernel's header files in a
+form suitable for use by userspace programs.
+
+The linux kernel's exported header files describe the API for user space
+programs attempting to use kernel services. These kernel header files are
+used by the system's C library (such as glibc or uClibc) to define available
+system calls, as well as constants and structures to be used with these
+system calls. The C library's header files include the kernel header files
+from the "linux" subdirectory. The system's libc headers are usually
+installed at the default location /usr/include and the kernel headers in
+subdirectories under that (most notably /usr/include/linux and
+/usr/include/asm).
+
+Kernel headers are backwards compatible, but not forwards compatible. This
+means that a program built against a C library using older kernel headers
+should run on a newer kernel (although it may not have access to new
+features), but a program built against newer kernel headers may not work on an
+older kernel.
+
+The "make headers_install" command can be run in the top level directory of the
+kernel source code (or using a standard out-of-tree build). It takes two
+optional arguments:
+
+ make headers_install ARCH=i386 INSTALL_HDR_PATH=/usr
+
+ARCH indicates which architecture to produce headers for, and defaults to the
+current architecture. The linux/asm directory of the exported kernel headers
+is platform-specific, to see a complete list of supported architectures use
+the command:
+
+ ls -d include/asm-* | sed 's/.*-//'
+
+INSTALL_HDR_PATH indicates where to install the headers. It defaults to
+"./usr".
+
+An 'include' directory is automatically created inside INSTALL_HDR_PATH and
+headers are installed in 'INSTALL_HDR_PATH/include'.
+
+The command "make headers_install_all" exports headers for all architectures
+simultaneously. (This is mostly of interest to distribution maintainers,
+who create an architecture-independent tarball from the resulting include
+directory.) You also can use HDR_ARCH_LIST to specify list of architectures.
+Remember to provide the appropriate linux/asm directory via "mv" or "ln -s"
+before building a C library with headers exported this way.
+
+The kernel header export infrastructure is maintained by David Woodhouse
+<dwmw2@infradead.org>.
diff --git a/Documentation/kbuild/kbuild.txt b/Documentation/kbuild/kbuild.txt
new file mode 100644
index 0000000..0ff6a46
--- /dev/null
+++ b/Documentation/kbuild/kbuild.txt
@@ -0,0 +1,240 @@
+Output files
+
+modules.order
+--------------------------------------------------
+This file records the order in which modules appear in Makefiles. This
+is used by modprobe to deterministically resolve aliases that match
+multiple modules.
+
+modules.builtin
+--------------------------------------------------
+This file lists all modules that are built into the kernel. This is used
+by modprobe to not fail when trying to load something builtin.
+
+
+Environment variables
+
+KCPPFLAGS
+--------------------------------------------------
+Additional options to pass when preprocessing. The preprocessing options
+will be used in all cases where kbuild does preprocessing including
+building C files and assembler files.
+
+KAFLAGS
+--------------------------------------------------
+Additional options to the assembler (for built-in and modules).
+
+AFLAGS_MODULE
+--------------------------------------------------
+Additional module specific options to use for $(AS).
+
+AFLAGS_KERNEL
+--------------------------------------------------
+Additional options for $(AS) when used for assembler
+code for code that is compiled as built-in.
+
+KCFLAGS
+--------------------------------------------------
+Additional options to the C compiler (for built-in and modules).
+
+CFLAGS_KERNEL
+--------------------------------------------------
+Additional options for $(CC) when used to compile
+code that is compiled as built-in.
+
+CFLAGS_MODULE
+--------------------------------------------------
+Additional module specific options to use for $(CC).
+
+LDFLAGS_MODULE
+--------------------------------------------------
+Additional options used for $(LD) when linking modules.
+
+LDFLAGS_vmlinux
+--------------------------------------------------
+Additional options passed to final link of vmlinux.
+
+KBUILD_VERBOSE
+--------------------------------------------------
+Set the kbuild verbosity. Can be assigned 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) Environment variable KBUILD_EXTMOD
+3) Environment 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 specified using "O=...".
+Setting "O=..." takes precedence over KBUILD_OUTPUT.
+
+KBUILD_DEBARCH
+--------------------------------------------------
+For the deb-pkg target, allows overriding the normal heuristics deployed by
+deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
+the UTS_MACHINE variable, and on some architectures also the kernel config.
+The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
+architecture.
+
+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 such as x86 and sparc have 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 in 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.
+
+INSTALLKERNEL
+--------------------------------------------------
+Install script called when using "make install".
+The default name is "installkernel".
+
+The script will be called with the following arguments:
+ $1 - kernel version
+ $2 - kernel image file
+ $3 - kernel map file
+ $4 - default install path (use root directory if blank)
+
+The implementation of "make install" is architecture specific
+and it may differ from the above.
+
+INSTALLKERNEL is provided to enable the possibility to
+specify a custom installer when cross compiling a kernel.
+
+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 value will be used as the options to the strip command.
+
+INSTALL_FW_PATH
+--------------------------------------------------
+INSTALL_FW_PATH specifies 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 specifies 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_SIGN_PIN
+--------------------------------------------------
+This variable allows a passphrase or PIN to be passed to the sign-file
+utility when signing kernel modules, if the private key requires such.
+
+KBUILD_MODPOST_WARN
+--------------------------------------------------
+KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
+symbols in the final module linking stage. It changes such errors
+into warnings.
+
+KBUILD_MODPOST_NOFINAL
+--------------------------------------------------
+KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
+This is solely useful to speed up test compiles.
+
+KBUILD_EXTRA_SYMBOLS
+--------------------------------------------------
+For modules that use symbols from other modules.
+See more details in modules.txt.
+
+ALLSOURCE_ARCHS
+--------------------------------------------------
+For tags/TAGS/cscope targets, you can specify more than one arch
+to be included in the databases, separated by blank space. E.g.:
+
+ $ make ALLSOURCE_ARCHS="x86 mips arm" tags
+
+To get all available archs you can also specify all. E.g.:
+
+ $ make ALLSOURCE_ARCHS=all tags
+
+KBUILD_ENABLE_EXTRA_GCC_CHECKS
+--------------------------------------------------
+If enabled over the make command line with "W=1", it turns on additional
+gcc -W... options for more extensive build-time checking.
+
+KBUILD_BUILD_TIMESTAMP
+--------------------------------------------------
+Setting this to a date string overrides the timestamp used in the
+UTS_VERSION definition (uname -v in the running kernel). The value has to
+be a string that can be passed to date -d. The default value
+is the output of the date command at one point during build.
+
+KBUILD_BUILD_USER, KBUILD_BUILD_HOST
+--------------------------------------------------
+These two variables allow to override the user@host string displayed during
+boot and in /proc/version. The default value is the output of the commands
+whoami and host, respectively.
+
+KBUILD_LDS
+--------------------------------------------------
+The linker script with full path. Assigned by the top-level Makefile.
+
+KBUILD_VMLINUX_INIT
+--------------------------------------------------
+All object files for the init (first) part of vmlinux.
+Files specified with KBUILD_VMLINUX_INIT are linked first.
+
+KBUILD_VMLINUX_MAIN
+--------------------------------------------------
+All object files for the main part of vmlinux.
+KBUILD_VMLINUX_INIT and KBUILD_VMLINUX_MAIN together specify
+all the object files used to link vmlinux.
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
new file mode 100644
index 0000000..c52856d
--- /dev/null
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -0,0 +1,556 @@
+Introduction
+------------
+
+The configuration database is a 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 on 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".
+
+- type definition + default value:
+ "def_bool"/"def_tristate" <expr> ["if" <expr>]
+ This is a shorthand notation for a type definition plus a value.
+ Optionally dependencies for this default value can be added with "if".
+
+- dependencies: "depends on" <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.
+ Note:
+ select should be used with care. select will force
+ a symbol to a value without visiting the dependencies.
+ By abusing select you are able to select a symbol FOO even
+ if FOO depends on BAR that is not set.
+ In general use select only for non-visible symbols
+ (no prompts anywhere) and for symbols with no dependencies.
+ That will limit the usefulness but on the other hand avoid
+ the illegal configurations all over.
+
+- limiting menu display: "visible if" <expr>
+ This attribute is only applicable to menu blocks, if the condition is
+ false, the menu block is not displayed to the user (the symbols
+ contained there can still be selected by other symbols, though). It is
+ similar to a conditional "prompt" attribute for individual menu
+ entries. Default value of "visible" is true.
+
+- 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 separate configuration logic from help within
+ the file as an aid to developers.
+
+- misc options: "option" <symbol>[=<value>]
+ Various less common options can be defined via this option syntax,
+ which can modify the behaviour of the menu entry and its config
+ symbol. These options are currently possible:
+
+ - "defconfig_list"
+ This declares a list of default entries which can be used when
+ looking for the default configuration (which is used when the main
+ .config doesn't exists yet.)
+
+ - "modules"
+ This declares the symbol to be used as the MODULES symbol, which
+ enables the third modular state for all config symbols.
+ At most one symbol may have the "modules" option set.
+
+ - "env"=<value>
+ This imports the environment variable into Kconfig. It behaves like
+ a default, except that the value comes from the environment, this
+ also means that the behaviour when mixing it with normal defaults is
+ undefined at this point. The symbol is currently not exported back
+ to the build environment (if this is desired, it can be done via
+ another symbol).
+
+ - "allnoconfig_y"
+ This declares the symbol as one that should have the value y when
+ using "allnoconfig". Used for symbols that hide other symbols.
+
+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 its
+expression evaluates to 'm' or 'y'.
+
+There are two types of symbols: constant and non-constant symbols.
+Non-constant symbols are the most common ones and are defined with the
+'config' statement. Non-constant 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 on 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 on MODULES
+
+comment "module support disabled"
+ depends on !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 similar 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" [symbol]
+ <choice options>
+ <choice block>
+ "endchoice"
+
+This defines a choice group and accepts any of the 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.
+If no [symbol] is associated with a choice, then you can not have multiple
+definitions of that choice. If a [symbol] is associated to the choice,
+then you may define the same choice (ie. with the same entries) in another
+place.
+
+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 and "visible"
+attributes.
+
+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.
+
+mainmenu:
+
+ "mainmenu" <prompt>
+
+This sets the config program's title bar if the config program chooses
+to use it. It should be placed at the top of the configuration, before any
+other statement.
+
+
+Kconfig hints
+-------------
+This is a collection of Kconfig tips, most of which aren't obvious at
+first glance and most of which have become idioms in several Kconfig
+files.
+
+Adding common features and make the usage configurable
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It is a common idiom to implement a feature/functionality that are
+relevant for some architectures but not all.
+The recommended way to do so is to use a config variable named HAVE_*
+that is defined in a common Kconfig file and selected by the relevant
+architectures.
+An example is the generic IOMAP functionality.
+
+We would in lib/Kconfig see:
+
+# Generic IOMAP is used to ...
+config HAVE_GENERIC_IOMAP
+
+config GENERIC_IOMAP
+ depends on HAVE_GENERIC_IOMAP && FOO
+
+And in lib/Makefile we would see:
+obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
+
+For each architecture using the generic IOMAP functionality we would see:
+
+config X86
+ select ...
+ select HAVE_GENERIC_IOMAP
+ select ...
+
+Note: we use the existing config option and avoid creating a new
+config variable to select HAVE_GENERIC_IOMAP.
+
+Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is
+introduced to overcome the limitation of select which will force a
+config option to 'y' no matter the dependencies.
+The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the
+situation where select forces a symbol equals to 'y'.
+
+Build as module only
+~~~~~~~~~~~~~~~~~~~~
+To restrict a component build to module-only, qualify its config symbol
+with "depends on m". E.g.:
+
+config FOO
+ depends on BAR && m
+
+limits FOO to module (=m) or disabled (=n).
+
+Kconfig recursive dependency limitations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you've hit the Kconfig error: "recursive dependency detected" you've run
+into a recursive dependency issue with Kconfig, a recursive dependency can be
+summarized as a circular dependency. The kconfig tools need to ensure that
+Kconfig files comply with specified configuration requirements. In order to do
+that kconfig must determine the values that are possible for all Kconfig
+symbols, this is currently not possible if there is a circular relation
+between two or more Kconfig symbols. For more details refer to the "Simple
+Kconfig recursive issue" subsection below. Kconfig does not do recursive
+dependency resolution; this has a few implications for Kconfig file writers.
+We'll first explain why this issues exists and then provide an example
+technical limitation which this brings upon Kconfig developers. Eager
+developers wishing to try to address this limitation should read the next
+subsections.
+
+Simple Kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Read: Documentation/kbuild/Kconfig.recursion-issue-01
+
+Test with:
+
+make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
+
+Cumulative Kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Read: Documentation/kbuild/Kconfig.recursion-issue-02
+
+Test with:
+
+make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
+
+Practical solutions to kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Developers who run into the recursive Kconfig issue have three options
+at their disposal. We document them below and also provide a list of
+historical issues resolved through these different solutions.
+
+ a) Remove any superfluous "select FOO" or "depends on FOO"
+ b) Match dependency semantics:
+ b1) Swap all "select FOO" to "depends on FOO" or,
+ b2) Swap all "depends on FOO" to "select FOO"
+
+The resolution to a) can be tested with the sample Kconfig file
+Documentation/kbuild/Kconfig.recursion-issue-01 through the removal
+of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already
+since CORE_BELL_A depends on CORE. At times it may not be possible to remove
+some dependency criteria, for such cases you can work with solution b).
+
+The two different resolutions for b) can be tested in the sample Kconfig file
+Documentation/kbuild/Kconfig.recursion-issue-02.
+
+Below is a list of examples of prior fixes for these types of recursive issues;
+all errors appear to involve one or more select's and one or more "depends on".
+
+commit fix
+====== ===
+06b718c01208 select A -> depends on A
+c22eacfe82f9 depends on A -> depends on B
+6a91e854442c select A -> depends on A
+118c565a8f2e select A -> select B
+f004e5594705 select A -> depends on A
+c7861f37b4c6 depends on A -> (null)
+80c69915e5fb select A -> (null) (1)
+c2218e26c0d0 select A -> depends on A (1)
+d6ae99d04e1c select A -> depends on A
+95ca19cf8cbf select A -> depends on A
+8f057d7bca54 depends on A -> (null)
+8f057d7bca54 depends on A -> select A
+a0701f04846e select A -> depends on A
+0c8b92f7f259 depends on A -> (null)
+e4e9e0540928 select A -> depends on A (2)
+7453ea886e87 depends on A > (null) (1)
+7b1fff7e4fdf select A -> depends on A
+86c747d2a4f0 select A -> depends on A
+d9f9ab51e55e select A -> depends on A
+0c51a4d8abd6 depends on A -> select A (3)
+e98062ed6dc4 select A -> depends on A (3)
+91e5d284a7f1 select A -> (null)
+
+(1) Partial (or no) quote of error.
+(2) That seems to be the gist of that fix.
+(3) Same error.
+
+Future kconfig work
+~~~~~~~~~~~~~~~~~~~
+
+Work on kconfig is welcomed on both areas of clarifying semantics and on
+evaluating the use of a full SAT solver for it. A full SAT solver can be
+desirable to enable more complex dependency mappings and / or queries,
+for instance on possible use case for a SAT solver could be that of handling
+the current known recursive dependency issues. It is not known if this would
+address such issues but such evaluation is desirable. If support for a full SAT
+solver proves too complex or that it cannot address recursive dependency issues
+Kconfig should have at least clear and well defined semantics which also
+addresses and documents limitations or requirements such as the ones dealing
+with recursive dependencies.
+
+Further work on both of these areas is welcomed on Kconfig. We elaborate
+on both of these in the next two subsections.
+
+Semantics of Kconfig
+~~~~~~~~~~~~~~~~~~~~
+
+The use of Kconfig is broad, Linux is now only one of Kconfig's users:
+one study has completed a broad analysis of Kconfig use in 12 projects [0].
+Despite its widespread use, and although this document does a reasonable job
+in documenting basic Kconfig syntax a more precise definition of Kconfig
+semantics is welcomed. One project deduced Kconfig semantics through
+the use of the xconfig configurator [1]. Work should be done to confirm if
+the deduced semantics matches our intended Kconfig design goals.
+
+Having well defined semantics can be useful for tools for practical
+evaluation of depenencies, for instance one such use known case was work to
+express in boolean abstraction of the inferred semantics of Kconfig to
+translate Kconfig logic into boolean formulas and run a SAT solver on this to
+find dead code / features (always inactive), 114 dead features were found in
+Linux using this methodology [1] (Section 8: Threats to validity).
+
+Confirming this could prove useful as Kconfig stands as one of the the leading
+industrial variability modeling languages [1] [2]. Its study would help
+evaluate practical uses of such languages, their use was only theoretical
+and real world requirements were not well understood. As it stands though
+only reverse engineering techniques have been used to deduce semantics from
+variability modeling languages such as Kconfig [3].
+
+[0] http://www.eng.uwaterloo.ca/~shshe/kconfig_semantics.pdf
+[1] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
+[2] http://gsd.uwaterloo.ca/sites/default/files/ase241-berger_0.pdf
+[3] http://gsd.uwaterloo.ca/sites/default/files/icse2011.pdf
+
+Full SAT solver for Kconfig
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Although SAT solvers [0] haven't yet been used by Kconfig directly, as noted in
+the previous subsection, work has been done however to express in boolean
+abstraction the inferred semantics of Kconfig to translate Kconfig logic into
+boolean formulas and run a SAT solver on it [1]. Another known related project
+is CADOS [2] (former VAMOS [3]) and the tools, mainly undertaker [4], which has
+been introduced first with [5]. The basic concept of undertaker is to exract
+variability models from Kconfig, and put them together with a propositional
+formula extracted from CPP #ifdefs and build-rules into a SAT solver in order
+to find dead code, dead files, and dead symbols. If using a SAT solver is
+desirable on Kconfig one approach would be to evaluate repurposing such efforts
+somehow on Kconfig. There is enough interest from mentors of existing projects
+to not only help advise how to integrate this work upstream but also help
+maintain it long term. Interested developers should visit:
+
+http://kernelnewbies.org/KernelProjects/kconfig-sat
+
+[0] http://www.cs.cornell.edu/~sabhar/chapters/SATSolvers-KR-Handbook.pdf
+[1] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
+[2] https://cados.cs.fau.de
+[3] https://vamos.cs.fau.de
+[4] https://undertaker.cs.fau.de
+[5] https://www4.cs.fau.de/Publications/2011/tartler_11_eurosys.pdf
diff --git a/Documentation/kbuild/kconfig.txt b/Documentation/kbuild/kconfig.txt
new file mode 100644
index 0000000..bbc99c0
--- /dev/null
+++ b/Documentation/kbuild/kconfig.txt
@@ -0,0 +1,237 @@
+This file contains some assistance for using "make *config".
+
+Use "make help" to list all of the possible configuration targets.
+
+The xconfig ('qconf') and menuconfig ('mconf') programs also
+have embedded help text. Be sure to check it for navigation,
+search, and other general help text.
+
+======================================================================
+General
+--------------------------------------------------
+
+New kernel releases often introduce new config symbols. Often more
+important, new kernel releases may rename config symbols. When
+this happens, using a previously working .config file and running
+"make oldconfig" won't necessarily produce a working new kernel
+for you, so you may find that you need to see what NEW kernel
+symbols have been introduced.
+
+To see a list of new config symbols when using "make oldconfig", use
+
+ cp user/some/old.config .config
+ make listnewconfig
+
+and the config program will list any new symbols, one per line.
+
+ scripts/diffconfig .config.old .config | less
+
+______________________________________________________________________
+Environment variables for '*config'
+
+KCONFIG_CONFIG
+--------------------------------------------------
+This environment variable can be used to specify a default kernel config
+file name to override the default name of ".config".
+
+KCONFIG_OVERWRITECONFIG
+--------------------------------------------------
+If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not
+break symlinks when .config is a symlink to somewhere else.
+
+CONFIG_
+--------------------------------------------------
+If you set CONFIG_ in the environment, Kconfig will prefix all symbols
+with its value when saving the configuration, instead of using the default,
+"CONFIG_".
+
+______________________________________________________________________
+Environment variables for '{allyes/allmod/allno/rand}config'
+
+KCONFIG_ALLCONFIG
+--------------------------------------------------
+(partially based on lkml email from/by Rob Landley, re: miniconfig)
+--------------------------------------------------
+The allyesconfig/allmodconfig/allnoconfig/randconfig variants can also
+use the environment variable KCONFIG_ALLCONFIG as a flag or a filename
+that contains config symbols that the user requires to be set to a
+specific value. If KCONFIG_ALLCONFIG is used without a filename where
+KCONFIG_ALLCONFIG == "" or KCONFIG_ALLCONFIG == "1", "make *config"
+checks for a file named "all{yes/mod/no/def/random}.config"
+(corresponding to the *config command that was used) for symbol values
+that are to be forced. If this file is not found, it checks for a
+file named "all.config" to contain forced values.
+
+This enables you to create "miniature" config (miniconfig) or custom
+config files containing just the config symbols that you are interested
+in. Then the kernel config system generates the full .config file,
+including symbols of your miniconfig file.
+
+This 'KCONFIG_ALLCONFIG' file is a config file which contains
+(usually a subset of all) preset config symbols. These variable
+settings are still subject to normal dependency checks.
+
+Examples:
+ KCONFIG_ALLCONFIG=custom-notebook.config make allnoconfig
+or
+ KCONFIG_ALLCONFIG=mini.config make allnoconfig
+or
+ make KCONFIG_ALLCONFIG=mini.config allnoconfig
+
+These examples will disable most options (allnoconfig) but enable or
+disable the options that are explicitly listed in the specified
+mini-config files.
+
+______________________________________________________________________
+Environment variables for 'randconfig'
+
+KCONFIG_SEED
+--------------------------------------------------
+You can set this to the integer value used to seed the RNG, if you want
+to somehow debug the behaviour of the kconfig parser/frontends.
+If not set, the current time will be used.
+
+KCONFIG_PROBABILITY
+--------------------------------------------------
+This variable can be used to skew the probabilities. This variable can
+be unset or empty, or set to three different formats:
+ KCONFIG_PROBABILITY y:n split y:m:n split
+ -----------------------------------------------------------------
+ unset or empty 50 : 50 33 : 33 : 34
+ N N : 100-N N/2 : N/2 : 100-N
+ [1] N:M N+M : 100-(N+M) N : M : 100-(N+M)
+ [2] N:M:L N : 100-N M : L : 100-(M+L)
+
+where N, M and L are integers (in base 10) in the range [0,100], and so
+that:
+ [1] N+M is in the range [0,100]
+ [2] M+L is in the range [0,100]
+
+Examples:
+ KCONFIG_PROBABILITY=10
+ 10% of booleans will be set to 'y', 90% to 'n'
+ 5% of tristates will be set to 'y', 5% to 'm', 90% to 'n'
+ KCONFIG_PROBABILITY=15:25
+ 40% of booleans will be set to 'y', 60% to 'n'
+ 15% of tristates will be set to 'y', 25% to 'm', 60% to 'n'
+ KCONFIG_PROBABILITY=10:15:15
+ 10% of booleans will be set to 'y', 90% to 'n'
+ 15% of tristates will be set to 'y', 15% to 'm', 70% to 'n'
+
+______________________________________________________________________
+Environment variables for 'silentoldconfig'
+
+KCONFIG_NOSILENTUPDATE
+--------------------------------------------------
+If this variable has a non-blank value, it prevents silent kernel
+config updates (requires explicit updates).
+
+KCONFIG_AUTOCONFIG
+--------------------------------------------------
+This environment variable can be set to specify the path & name of the
+"auto.conf" file. Its default value is "include/config/auto.conf".
+
+KCONFIG_TRISTATE
+--------------------------------------------------
+This environment variable can be set to specify the path & name of the
+"tristate.conf" file. Its default value is "include/config/tristate.conf".
+
+KCONFIG_AUTOHEADER
+--------------------------------------------------
+This environment variable can be set to specify the path & name of the
+"autoconf.h" (header) file.
+Its default value is "include/generated/autoconf.h".
+
+
+======================================================================
+menuconfig
+--------------------------------------------------
+
+SEARCHING for CONFIG symbols
+
+Searching in menuconfig:
+
+ The Search function searches for kernel configuration symbol
+ names, so you have to know something close to what you are
+ looking for.
+
+ Example:
+ /hotplug
+ This lists all config symbols that contain "hotplug",
+ e.g., HOTPLUG_CPU, MEMORY_HOTPLUG.
+
+ For search help, enter / followed TAB-TAB-TAB (to highlight
+ <Help>) and Enter. This will tell you that you can also use
+ regular expressions (regexes) in the search string, so if you
+ are not interested in MEMORY_HOTPLUG, you could try
+
+ /^hotplug
+
+ When searching, symbols are sorted thus:
+ - first, exact matches, sorted alphabetically (an exact match
+ is when the search matches the complete symbol name);
+ - then, other matches, sorted alphabetically.
+ For example: ^ATH.K matches:
+ ATH5K ATH9K ATH5K_AHB ATH5K_DEBUG [...] ATH6KL ATH6KL_DEBUG
+ [...] ATH9K_AHB ATH9K_BTCOEX_SUPPORT ATH9K_COMMON [...]
+ of which only ATH5K and ATH9K match exactly and so are sorted
+ first (and in alphabetical order), then come all other symbols,
+ sorted in alphabetical order.
+
+______________________________________________________________________
+User interface options for 'menuconfig'
+
+MENUCONFIG_COLOR
+--------------------------------------------------
+It is possible to select different color themes using the variable
+MENUCONFIG_COLOR. To select a theme use:
+
+ make MENUCONFIG_COLOR=<theme> menuconfig
+
+Available themes are:
+ mono => selects colors suitable for monochrome displays
+ blackbg => selects a color scheme with black background
+ classic => theme with blue background. The classic look
+ bluetitle => a LCD friendly version of classic. (default)
+
+MENUCONFIG_MODE
+--------------------------------------------------
+This mode shows all sub-menus in one large tree.
+
+Example:
+ make MENUCONFIG_MODE=single_menu menuconfig
+
+
+======================================================================
+xconfig
+--------------------------------------------------
+
+Searching in xconfig:
+
+ The Search function searches for kernel configuration symbol
+ names, so you have to know something close to what you are
+ looking for.
+
+ Example:
+ Ctrl-F hotplug
+ or
+ Menu: File, Search, hotplug
+
+ lists all config symbol entries that contain "hotplug" in
+ the symbol name. In this Search dialog, you may change the
+ config setting for any of the entries that are not grayed out.
+ You can also enter a different search string without having
+ to return to the main menu.
+
+
+======================================================================
+gconfig
+--------------------------------------------------
+
+Searching in gconfig:
+
+ None (gconfig isn't maintained as well as xconfig or menuconfig);
+ however, gconfig does have a few more viewing choices than
+ xconfig does.
+
+###
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
new file mode 100644
index 0000000..13f888a
--- /dev/null
+++ b/Documentation/kbuild/makefiles.txt
@@ -0,0 +1,1418 @@
+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
+ --- 3.11 $(CC) support functions
+ --- 3.12 $(LD) support functions
+
+ === 4 Host Program support
+ --- 4.1 Simple Host Program
+ --- 4.2 Composite Host Programs
+ --- 4.3 Using C++ for host programs
+ --- 4.4 Controlling compiler options for host programs
+ --- 4.5 When host programs are actually built
+ --- 4.6 Using hostprogs-$(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 archheaders:
+ --- 6.3 Add prerequisites to archprepare:
+ --- 6.4 List directories to visit when descending
+ --- 6.5 Architecture-specific boot images
+ --- 6.6 Building non-kbuild targets
+ --- 6.7 Commands useful for building a boot image
+ --- 6.8 Custom kbuild commands
+ --- 6.9 Preprocessing linker scripts
+ --- 6.10 Generic header files
+
+ === 7 Kbuild syntax for exported headers
+ --- 7.1 header-y
+ --- 7.2 genhdr-y
+ --- 7.3 destination-y
+ --- 7.4 generic-y
+
+ === 8 Kbuild Variables
+ === 9 Makefile language
+ === 10 Credits
+ === 11 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 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 introduces the syntax used in the
+kbuild makefiles.
+The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can
+be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild'
+file will be used.
+
+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 tells 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 $(obj-y) lists. 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 $(obj-y) is significant. Duplicates in
+ the lists are allowed: the first instance will be linked into
+ built-in.o and succeeding instances will be ignored.
+
+ Link order is significant, because certain functions
+ (module_init() / __initcall) will be called during boot in the
+ order they appear. So keep in mind that changing the link
+ order may e.g. change the order in which your SCSI
+ controllers are detected, and thus your disks are renumbered.
+
+ Example:
+ #drivers/isdn/i4l/Makefile
+ # Makefile for the kernel ISDN subsystem and device drivers.
+ # Each configuration option enables a list of files.
+ obj-$(CONFIG_ISDN_I4L) += isdn.o
+ obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
+
+--- 3.3 Loadable module goals - obj-m
+
+ $(obj-m) specifies 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; however,
+ kbuild needs to know which object files you want to build your
+ module from, so you have to tell it by setting a $(<module_name>-y)
+ variable.
+
+ Example:
+ #drivers/isdn/i4l/Makefile
+ obj-$(CONFIG_ISDN_I4L) += isdn.o
+ isdn-y := 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 $(isdn-y) and then run
+ "$(LD) -r" on the list of these files to generate isdn.o.
+
+ Due to kbuild recognizing $(<module_name>-y) for composite objects,
+ you can use the value of a CONFIG_ symbol to optionally include an
+ object file as part of a composite object.
+
+ Example:
+ #fs/ext2/Makefile
+ obj-$(CONFIG_EXT2_FS) += ext2.o
+ ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \
+ namei.o super.o symlink.o
+ ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \
+ xattr_trusted.o
+
+ In this example, xattr.o, xattr_user.o and xattr_trusted.o are 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 additionally listed in
+ lib-y will not be included in the library, since they will
+ be accessible anyway.
+ 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/x86/lib/Makefile
+ lib-y := delay.o
+
+ This will create a library lib.a based on delay.o. For kbuild to
+ actually recognize that there is a lib.a being built, the directory
+ shall be listed in libs-y.
+ See also "6.4 List directories to visit when descending".
+
+ Use 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 modular 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
+
+ ccflags-y, asflags-y and ldflags-y
+ These three flags apply only to the kbuild makefile in which they
+ are assigned. They are used for all the normal cc, as and ld
+ invocations happening during a recursive build.
+ Note: Flags with the same behaviour were previously named:
+ EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS.
+ They are still supported but their usage is deprecated.
+
+ ccflags-y specifies options for compiling with $(CC).
+
+ Example:
+ # drivers/acpi/Makefile
+ ccflags-y := -Os
+ ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT
+
+ This variable is necessary because the top Makefile owns the
+ variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
+ entire tree.
+
+ asflags-y specifies options for assembling with $(AS).
+
+ Example:
+ #arch/sparc/kernel/Makefile
+ asflags-y := -ansi
+
+ ldflags-y specifies options for linking with $(LD).
+
+ Example:
+ #arch/cris/boot/compressed/Makefile
+ ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds
+
+ subdir-ccflags-y, subdir-asflags-y
+ The two flags listed above are similar to ccflags-y and asflags-y.
+ The difference is that the subdir- variants have effect for the kbuild
+ file where they are present and all subdirectories.
+ Options specified using subdir-* are added to the commandline before
+ the options specified using the non-subdir variants.
+
+ Example:
+ subdir-ccflags-y := -Werror
+
+ CFLAGS_$@, 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
+
+ These two lines specify compilation flags for aha152x.o and gdth.o.
+
+ $(AFLAGS_$@) is a similar feature for source files in assembly
+ languages.
+
+ Example:
+ # arch/arm/kernel/Makefile
+ AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
+ AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312
+ AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt
+
+
+--- 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 are the architecture-specific Makefiles which
+ need 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).
+
+ $(kecho)
+ echoing information to user in a rule is often a good practice
+ but when execution "make -s" one does not expect to see any output
+ except for warnings/errors.
+ To support this kbuild defines $(kecho) which will echo out the
+ text following $(kecho) to stdout except if "make -s" is used.
+
+ Example:
+ #arch/blackfin/boot/Makefile
+ $(obj)/vmImage: $(obj)/vmlinux.gz
+ $(call if_changed,uimage)
+ @$(kecho) 'Kernel: $@ is ready'
+
+
+--- 3.11 $(CC) support functions
+
+ The kernel may be built with several different versions of
+ $(CC), each supporting a unique set of features and options.
+ kbuild provides basic support to check for valid options for $(CC).
+ $(CC) is usually the gcc compiler, but other alternatives are
+ available.
+
+ as-option
+ as-option is used to check if $(CC) -- when used to compile
+ assembler (*.S) files -- supports the given option. An optional
+ second option may be specified if the first option is not supported.
+
+ Example:
+ #arch/sh/Makefile
+ cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),)
+
+ In the above example, cflags-y will be assigned the option
+ -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC).
+ The second argument is optional, and if supplied will be used
+ if first argument is not supported.
+
+ cc-ldoption
+ cc-ldoption is used to check if $(CC) when used to link object files
+ supports the given option. An optional second option may be
+ specified if first option are not supported.
+
+ Example:
+ #arch/x86/kernel/Makefile
+ vsyscall-flags += $(call cc-ldoption, -Wl$(comma)--hash-style=sysv)
+
+ In the above example, vsyscall-flags will be assigned the option
+ -Wl$(comma)--hash-style=sysv if it is supported by $(CC).
+ The second argument is optional, and if supplied will be used
+ if first argument is not supported.
+
+ as-instr
+ as-instr checks if the assembler reports a specific instruction
+ and then outputs either option1 or option2
+ C escapes are supported in the test instruction
+ Note: as-instr-option uses KBUILD_AFLAGS for $(AS) options
+
+ cc-option
+ cc-option is used to check if $(CC) supports a given option, and if
+ not supported to use an optional second option.
+
+ Example:
+ #arch/x86/Makefile
+ cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
+
+ In the above example, cflags-y will be assigned the option
+ -march=pentium-mmx if supported by $(CC), otherwise -march=i586.
+ The second argument to cc-option is optional, and if omitted,
+ cflags-y will be assigned no value if first option is not supported.
+ Note: cc-option uses KBUILD_CFLAGS for $(CC) options
+
+ cc-option-yn
+ cc-option-yn is used to check if gcc supports a given option
+ and return 'y' if supported, otherwise 'n'.
+
+ Example:
+ #arch/ppc/Makefile
+ biarch := $(call cc-option-yn, -m32)
+ aflags-$(biarch) += -a32
+ cflags-$(biarch) += -m32
+
+ In the above example, $(biarch) is set to y if $(CC) supports the -m32
+ option. When $(biarch) equals 'y', the expanded variables $(aflags-y)
+ and $(cflags-y) will be assigned the values -a32 and -m32,
+ respectively.
+ Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options
+
+ cc-option-align
+ gcc versions >= 3.0 changed the type of options used to specify
+ alignment of functions, loops etc. $(cc-option-align), when used
+ as prefix to the align options, will select the right prefix:
+ gcc < 3.00
+ cc-option-align = -malign
+ gcc >= 3.00
+ cc-option-align = -falign
+
+ Example:
+ KBUILD_CFLAGS += $(cc-option-align)-functions=4
+
+ In the above example, the option -falign-functions=4 is used for
+ gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used.
+ Note: cc-option-align uses KBUILD_CFLAGS for $(CC) options
+
+ cc-disable-warning
+ cc-disable-warning checks if gcc supports a given warning and returns
+ the commandline switch to disable it. This special function is needed,
+ because gcc 4.4 and later accept any unknown -Wno-* option and only
+ warn about it if there is another warning in the source file.
+
+ Example:
+ KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
+
+ In the above example, -Wno-unused-but-set-variable will be added to
+ KBUILD_CFLAGS only if gcc really accepts it.
+
+ cc-version
+ cc-version returns a numerical version of the $(CC) compiler version.
+ The format is <major><minor> where both are two digits. So for example
+ gcc 3.41 would return 0341.
+ cc-version is useful when a specific $(CC) version is faulty in one
+ area, for example -mregparm=3 was broken in some gcc versions
+ even though the option was accepted by gcc.
+
+ Example:
+ #arch/x86/Makefile
+ cflags-y += $(shell \
+ if [ $(cc-version) -ge 0300 ] ; then \
+ echo "-mregparm=3"; fi ;)
+
+ In the above example, -mregparm=3 is only used for gcc version greater
+ than or equal to gcc 3.0.
+
+ cc-ifversion
+ cc-ifversion tests the version of $(CC) and equals the fourth parameter
+ if version expression is true, or the fifth (if given) if the version
+ expression is false.
+
+ Example:
+ #fs/reiserfs/Makefile
+ ccflags-y := $(call cc-ifversion, -lt, 0402, -O1)
+
+ In this example, ccflags-y will be assigned the value -O1 if the
+ $(CC) version is less than 4.2.
+ cc-ifversion takes all the shell operators:
+ -eq, -ne, -lt, -le, -gt, and -ge
+ The third parameter may be a text as in this example, but it may also
+ be an expanded variable or a macro.
+
+ cc-fullversion
+ cc-fullversion is useful when the exact version of gcc is needed.
+ One typical use-case is when a specific GCC version is broken.
+ cc-fullversion points out a more specific version than cc-version does.
+
+ Example:
+ #arch/powerpc/Makefile
+ $(Q)if test "$(cc-fullversion)" = "040200" ; then \
+ echo -n '*** GCC-4.2.0 cannot compile the 64-bit powerpc ' ; \
+ false ; \
+ fi
+
+ In this example for a specific GCC version the build will error out
+ explaining to the user why it stops.
+
+ cc-cross-prefix
+ cc-cross-prefix is used to check if there exists a $(CC) in path with
+ one of the listed prefixes. The first prefix where there exist a
+ prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found
+ then nothing is returned.
+ Additional prefixes are separated by a single space in the
+ call of cc-cross-prefix.
+ This functionality is useful for architecture Makefiles that try
+ to set CROSS_COMPILE to well-known values but may have several
+ values to select between.
+ It is recommended only to try to set CROSS_COMPILE if it is a cross
+ build (host arch is different from target arch). And if CROSS_COMPILE
+ is already set then leave it with the old value.
+
+ Example:
+ #arch/m68k/Makefile
+ ifneq ($(SUBARCH),$(ARCH))
+ ifeq ($(CROSS_COMPILE),)
+ CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-)
+ endif
+ endif
+
+--- 3.12 $(LD) support functions
+
+ ld-option
+ ld-option is used to check if $(LD) supports the supplied option.
+ ld-option takes two options as arguments.
+ The second argument is an optional option that can be used if the
+ first option is not supported by $(LD).
+
+ Example:
+ #Makefile
+ LDFLAGS_vmlinux += $(call ld-option, -X)
+
+
+=== 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.
+ $(<executable>-objs) lists 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 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 of 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
+
+--- 4.4 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".
+
+--- 4.5 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 := $(hostprogs-y)
+
+ This will tell kbuild to build lxdialog even if not referenced in
+ any rule.
+
+--- 4.6 Using hostprogs-$(CONFIG_FOO)
+
+ A typical pattern in a Kbuild file looks 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 evaluates to 'm', kbuild will still build
+ the binary. In other words, Kbuild handles hostprogs-m exactly
+ like hostprogs-y. But only hostprogs-y is recommended to be used
+ when no CONFIG symbols are involved.
+
+=== 5 Kbuild clean infrastructure
+
+"make clean" deletes most generated files in the obj 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:
+ #lib/Makefile
+ clean-files := crc32table.h
+
+When executing "make clean", the file "crc32table.h" will be deleted.
+Kbuild will assume files to be in the same relative directory as the
+Makefile, except if prefixed with $(objtree).
+
+To delete a directory hierarchy use:
+
+ Example:
+ #scripts/package/Makefile
+ clean-dirs := $(objtree)/debian/
+
+This will delete the directory debian in the toplevel directory, including all
+subdirectories.
+
+To exclude certain files from make clean, use the $(no-clean-files) variable.
+This is only a special case used in the top level Kbuild file:
+
+ Example:
+ #Kbuild
+ no-clean-files := $(bounds-file) $(offsets-file)
+
+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/x86/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 build the
+final bootimage there is an optional target named archclean:
+
+ Example:
+ #arch/x86/Makefile
+ archclean:
+ $(Q)$(MAKE) $(clean)=arch/x86/boot
+
+When "make clean" is executed, make will descend down in arch/x86/boot,
+and clean as usual. The Makefile located in arch/x86/boot/ may use
+the subdir- trick to descend further down.
+
+Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is
+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
+arch/$(ARCH)/Makefile contains what is required to set up kbuild
+for said architecture.
+To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines
+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/$(ARCH)/Makefile
+4) Recursively descend down in all directories listed in
+ init-* core* drivers-* net-* libs-* and build all targets.
+ - The values of the above variables are expanded in arch/$(ARCH)/Makefile.
+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.
+6) 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: ldflags-y can be used to further customise
+ the flags used. See chapter 3.7.
+
+ 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 $(LD) when linking vmlinux
+
+ LDFLAGS_vmlinux is used to specify additional flags to pass to
+ the linker when linking the final vmlinux image.
+ LDFLAGS_vmlinux uses the LDFLAGS_$@ support.
+
+ Example:
+ #arch/x86/Makefile
+ LDFLAGS_vmlinux := -e stext
+
+ OBJCOPYFLAGS objcopy flags
+
+ When $(call if_changed,objcopy) is used to translate a .o file,
+ 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.
+
+ KBUILD_AFLAGS $(AS) assembler flags
+
+ Default value - see top level Makefile
+ Append or modify as required per architecture.
+
+ Example:
+ #arch/sparc64/Makefile
+ KBUILD_AFLAGS += -m64 -mcpu=ultrasparc
+
+ KBUILD_CFLAGS $(CC) compiler flags
+
+ Default value - see top level Makefile
+ Append or modify as required per architecture.
+
+ Often, the KBUILD_CFLAGS variable depends on the configuration.
+
+ Example:
+ #arch/x86/boot/compressed/Makefile
+ cflags-$(CONFIG_X86_32) := -march=i386
+ cflags-$(CONFIG_X86_64) := -mcmodel=small
+ KBUILD_CFLAGS += $(cflags-y)
+
+ Many arch Makefiles dynamically run the target C compiler to
+ probe supported options:
+
+ #arch/x86/Makefile
+
+ ...
+ cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\
+ -march=pentium2,-march=i686)
+ ...
+ # Disable unit-at-a-time mode ...
+ KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time)
+ ...
+
+
+ The first example utilises the trick that a config option expands
+ to 'y' when selected.
+
+ KBUILD_AFLAGS_KERNEL $(AS) options specific for built-in
+
+ $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile
+ resident kernel code.
+
+ KBUILD_AFLAGS_MODULE Options for $(AS) when building modules
+
+ $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that
+ are used for $(AS).
+ From commandline AFLAGS_MODULE shall be used (see kbuild.txt).
+
+ KBUILD_CFLAGS_KERNEL $(CC) options specific for built-in
+
+ $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile
+ resident kernel code.
+
+ KBUILD_CFLAGS_MODULE Options for $(CC) when building modules
+
+ $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that
+ are used for $(CC).
+ From commandline CFLAGS_MODULE shall be used (see kbuild.txt).
+
+ KBUILD_LDFLAGS_MODULE Options for $(LD) when linking modules
+
+ $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options
+ used when linking modules. This is often a linker script.
+ From commandline LDFLAGS_MODULE shall be used (see kbuild.txt).
+
+ KBUILD_ARFLAGS Options for $(AR) when creating archives
+
+ $(KBUILD_ARFLAGS) set by the top level Makefile to "D" (deterministic
+ mode) if this option is supported by $(AR).
+
+ ARCH_CPPFLAGS, ARCH_AFLAGS, ARCH_CFLAGS Overrides the kbuild defaults
+
+ These variables are appended to the KBUILD_CPPFLAGS,
+ KBUILD_AFLAGS, and KBUILD_CFLAGS, respectively, after the
+ top-level Makefile has set any other flags. This provides a
+ means for an architecture to override the defaults.
+
+
+--- 6.2 Add prerequisites to archheaders:
+
+ The archheaders: rule is used to generate header files that
+ may be installed into user space by "make header_install" or
+ "make headers_install_all". In order to support
+ "make headers_install_all", this target has to be able to run
+ on an unconfigured tree, or a tree configured for another
+ architecture.
+
+ It is run before "make archprepare" when run on the
+ architecture itself.
+
+
+--- 6.3 Add prerequisites to archprepare:
+
+ The archprepare: rule is used to list prerequisites that need to be
+ built before starting to descend down in the subdirectories.
+ This is usually used for header files containing assembler constants.
+
+ Example:
+ #arch/arm/Makefile
+ archprepare: maketools
+
+ In this example, the file target maketools will be processed
+ before descending down in the subdirectories.
+ See also chapter XXX-TODO that describe how kbuild supports
+ generating offset header files.
+
+
+--- 6.4 List directories to visit when descending
+
+ An arch Makefile cooperates with the top Makefile to define variables
+ which specify how to build the vmlinux file. Note that there is no
+ corresponding arch-specific section for modules; the module-building
+ machinery is all architecture-independent.
+
+
+ head-y, init-y, core-y, libs-y, drivers-y, net-y
+
+ $(head-y) lists objects to be linked first in vmlinux.
+ $(libs-y) lists directories where a lib.a archive can be located.
+ The rest list directories where a built-in.o object file can be
+ located.
+
+ $(init-y) objects will be located after $(head-y).
+ Then the rest follows in this order:
+ $(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 directories.
+
+ Example:
+ #arch/sparc64/Makefile
+ core-y += arch/sparc64/kernel/
+ libs-y += arch/sparc64/prom/ arch/sparc64/lib/
+ drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/
+
+
+--- 6.5 Architecture-specific boot images
+
+ An arch Makefile specifies goals that take the vmlinux file, compress
+ it, wrap it in bootstrapping code, and copy the resulting files
+ somewhere. This includes various kinds of installation commands.
+ The actual goals are not standardized across architectures.
+
+ It is common to locate any additional processing in a boot/
+ directory below arch/$(ARCH)/.
+
+ Kbuild does not provide any smart way to support building a
+ target specified in boot/. Therefore arch/$(ARCH)/Makefile shall
+ call make manually to build a target in boot/.
+
+ The recommended approach is to include shortcuts in
+ arch/$(ARCH)/Makefile, and use the full path when calling down
+ into the arch/$(ARCH)/boot/Makefile.
+
+ Example:
+ #arch/x86/Makefile
+ boot := arch/x86/boot
+ bzImage: vmlinux
+ $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
+
+ "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke
+ make in a subdirectory.
+
+ There are no rules for naming architecture-specific targets,
+ but executing "make help" will list all relevant targets.
+ To support this, $(archhelp) must be defined.
+
+ Example:
+ #arch/x86/Makefile
+ define archhelp
+ echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)'
+ endif
+
+ When make is executed without arguments, the first goal encountered
+ will be built. In the top level Makefile the first goal present
+ is all:.
+ An architecture shall always, per default, build a bootable image.
+ In "make help", the default goal is highlighted with a '*'.
+ Add a new prerequisite to all: to select a default goal different
+ from vmlinux.
+
+ Example:
+ #arch/x86/Makefile
+ all: bzImage
+
+ When "make" is executed without arguments, bzImage will be built.
+
+--- 6.6 Building non-kbuild targets
+
+ extra-y
+
+ extra-y specifies additional targets created in the current
+ directory, in addition to any targets specified by obj-*.
+
+ Listing all targets in extra-y is required for two purposes:
+ 1) Enable kbuild to check changes in command lines
+ - When $(call if_changed,xxx) is used
+ 2) kbuild knows what files to delete during "make clean"
+
+ Example:
+ #arch/x86/kernel/Makefile
+ extra-y := head.o init_task.o
+
+ In this example, extra-y is used to list object files that
+ shall be built, but shall not be linked as part of built-in.o.
+
+
+--- 6.7 Commands useful for building a boot image
+
+ Kbuild provides a few macros that are useful when building a
+ boot image.
+
+ if_changed
+
+ if_changed is the infrastructure used for the following commands.
+
+ Usage:
+ target: source(s) FORCE
+ $(call if_changed,ld/objcopy/gzip/...)
+
+ When the rule is evaluated, it is checked to see if any files
+ need an update, or the command line has changed since the last
+ invocation. The latter will force a rebuild if any options
+ to the executable have changed.
+ Any target that utilises if_changed must be listed in $(targets),
+ otherwise the command line check will fail, and the target will
+ always be built.
+ Assignments to $(targets) are without $(obj)/ prefix.
+ if_changed may be used in conjunction with custom commands as
+ defined in 6.8 "Custom kbuild commands".
+
+ Note: It is a typical mistake to forget the FORCE prerequisite.
+ Another common pitfall is that whitespace is sometimes
+ significant; for instance, the below will fail (note the extra space
+ after the comma):
+ target: source(s) FORCE
+ #WRONG!# $(call if_changed, ld/objcopy/gzip/...)
+
+ ld
+ Link target. Often, LDFLAGS_$@ is used to set specific options to ld.
+
+ objcopy
+ Copy binary. Uses OBJCOPYFLAGS usually specified in
+ arch/$(ARCH)/Makefile.
+ OBJCOPYFLAGS_$@ may be used to set additional options.
+
+ gzip
+ Compress target. Use maximum compression to compress target.
+
+ Example:
+ #arch/x86/boot/Makefile
+ LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary
+ LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext
+
+ targets += setup setup.o bootsect bootsect.o
+ $(obj)/setup $(obj)/bootsect: %: %.o FORCE
+ $(call if_changed,ld)
+
+ In this example, there are two possible targets, requiring different
+ options to the linker. The linker options are specified using the
+ LDFLAGS_$@ syntax - one for each potential target.
+ $(targets) are assigned all potential targets, by which kbuild knows
+ the targets and will:
+ 1) check for commandline changes
+ 2) delete target during make clean
+
+ The ": %: %.o" part of the prerequisite is a shorthand that
+ frees us from listing the setup.o and bootsect.o files.
+ Note: It is a common mistake to forget the "targets :=" assignment,
+ resulting in the target file being recompiled for no
+ obvious reason.
+
+ dtc
+ Create flattened device tree blob object suitable for linking
+ into vmlinux. Device tree blobs linked into vmlinux are placed
+ in an init section in the image. Platform code *must* copy the
+ blob to non-init memory prior to calling unflatten_device_tree().
+
+ To use this command, simply add *.dtb into obj-y or targets, or make
+ some other target depend on %.dtb
+
+ A central rule exists to create $(obj)/%.dtb from $(src)/%.dts;
+ architecture Makefiles do no need to explicitly write out that rule.
+
+ Example:
+ targets += $(dtb-y)
+ clean-files += *.dtb
+ DTC_FLAGS ?= -p 1024
+
+--- 6.8 Custom kbuild commands
+
+ When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand
+ of a command is normally displayed.
+ To enable this behaviour for custom commands kbuild requires
+ two variables to be set:
+ quiet_cmd_<command> - what shall be echoed
+ cmd_<command> - the command to execute
+
+ Example:
+ #
+ quiet_cmd_image = BUILD $@
+ cmd_image = $(obj)/tools/build $(BUILDFLAGS) \
+ $(obj)/vmlinux.bin > $@
+
+ targets += bzImage
+ $(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE
+ $(call if_changed,image)
+ @echo 'Kernel: $@ is ready'
+
+ When updating the $(obj)/bzImage target, the line
+
+ BUILD arch/x86/boot/bzImage
+
+ will be displayed with "make KBUILD_VERBOSE=0".
+
+
+--- 6.9 Preprocessing linker scripts
+
+ When the vmlinux image is built, the linker script
+ arch/$(ARCH)/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.
+
+ Example:
+ #arch/x86/kernel/Makefile
+ always := vmlinux.lds
+
+ #Makefile
+ export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
+
+ The assignment to $(always) is used to tell kbuild to build the
+ target vmlinux.lds.
+ The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the
+ specified options when building the target vmlinux.lds.
+
+ When building the *.lds target, kbuild uses the variables:
+ KBUILD_CPPFLAGS : Set in top-level Makefile
+ cppflags-y : May be set in the kbuild makefile
+ CPPFLAGS_$(@F) : Target-specific flags.
+ Note that the full filename is used in this
+ assignment.
+
+ The kbuild infrastructure for *lds files is used in several
+ architecture-specific files.
+
+--- 6.10 Generic header files
+
+ The directory include/asm-generic contains the header files
+ that may be shared between individual architectures.
+ The recommended approach how to use a generic header file is
+ to list the file in the Kbuild file.
+ See "7.4 generic-y" for further info on syntax etc.
+
+=== 7 Kbuild syntax for exported headers
+
+The kernel includes a set of headers that is exported to userspace.
+Many headers can be exported as-is but other headers require a
+minimal pre-processing before they are ready for user-space.
+The pre-processing does:
+- drop kernel-specific annotations
+- drop include of compiler.h
+- drop all sections that are kernel internal (guarded by ifdef __KERNEL__)
+
+Each relevant directory contains a file name "Kbuild" which specifies the
+headers to be exported.
+See subsequent chapter for the syntax of the Kbuild file.
+
+ --- 7.1 header-y
+
+ header-y specifies header files to be exported.
+
+ Example:
+ #include/linux/Kbuild
+ header-y += usb/
+ header-y += aio_abi.h
+
+ The convention is to list one file per line and
+ preferably in alphabetic order.
+
+ header-y also specifies which subdirectories to visit.
+ A subdirectory is identified by a trailing '/' which
+ can be seen in the example above for the usb subdirectory.
+
+ Subdirectories are visited before their parent directories.
+
+ --- 7.2 genhdr-y
+
+ genhdr-y specifies generated files to be exported.
+ Generated files are special as they need to be looked
+ up in another directory when doing 'make O=...' builds.
+
+ Example:
+ #include/linux/Kbuild
+ genhdr-y += version.h
+
+ --- 7.3 destination-y
+
+ When an architecture has a set of exported headers that needs to be
+ exported to a different directory destination-y is used.
+ destination-y specifies the destination directory for all exported
+ headers in the file where it is present.
+
+ Example:
+ #arch/xtensa/platforms/s6105/include/platform/Kbuild
+ destination-y := include/linux
+
+ In the example above all exported headers in the Kbuild file
+ will be located in the directory "include/linux" when exported.
+
+ --- 7.4 generic-y
+
+ If an architecture uses a verbatim copy of a header from
+ include/asm-generic then this is listed in the file
+ arch/$(ARCH)/include/asm/Kbuild like this:
+
+ Example:
+ #arch/x86/include/asm/Kbuild
+ generic-y += termios.h
+ generic-y += rtc.h
+
+ During the prepare phase of the build a wrapper include
+ file is generated in the directory:
+
+ arch/$(ARCH)/include/generated/asm
+
+ When a header is exported where the architecture uses
+ the generic header a similar wrapper is generated as part
+ of the set of exported headers in the directory:
+
+ usr/include/asm
+
+ The generated wrapper will in both cases look like the following:
+
+ Example: termios.h
+ #include <asm-generic/termios.h>
+
+=== 8 Kbuild Variables
+
+The top Makefile exports the following variables:
+
+ VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION
+
+ These variables define the current kernel version. A few arch
+ Makefiles actually use these values directly; they should use
+ $(KERNELRELEASE) instead.
+
+ $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic
+ three-part version number, such as "2", "4", and "0". These three
+ values are always numeric.
+
+ $(EXTRAVERSION) defines an even tinier sublevel for pre-patches
+ or additional patches. It is usually some non-numeric string
+ such as "-pre4", and is often blank.
+
+ KERNELRELEASE
+
+ $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable
+ for constructing installation directory names or showing in
+ version strings. Some arch Makefiles use it for this purpose.
+
+ ARCH
+
+ This variable defines the target architecture, such as "i386",
+ "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to
+ determine which files to compile.
+
+ By default, the top Makefile sets $(ARCH) to be the same as the
+ host system architecture. For a cross build, a user may
+ override the value of $(ARCH) on the command line:
+
+ make ARCH=m68k ...
+
+
+ INSTALL_PATH
+
+ This variable defines a place for the arch Makefiles to install
+ the resident kernel image and System.map file.
+ Use this for architecture-specific install targets.
+
+ INSTALL_MOD_PATH, MODLIB
+
+ $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module
+ installation. This variable is not defined in the Makefile but
+ may be passed in by the user if desired.
+
+ $(MODLIB) specifies the directory for module installation.
+ The top Makefile defines $(MODLIB) to
+ $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may
+ override this value on the command line if desired.
+
+ INSTALL_MOD_STRIP
+
+ If this variable is specified, it 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, the
+ INSTALL_MOD_STRIP value will be used as the option(s) to the strip
+ command.
+
+
+=== 9 Makefile language
+
+The kernel Makefiles are designed to be run with GNU Make. The Makefiles
+use only the documented features of GNU Make, but they do use many
+GNU extensions.
+
+GNU Make supports elementary list-processing functions. The kernel
+Makefiles use a novel style of list building and manipulation with few
+"if" statements.
+
+GNU Make has two assignment operators, ":=" and "=". ":=" performs
+immediate evaluation of the right-hand side and stores an actual string
+into the left-hand side. "=" is like a formula definition; it stores the
+right-hand side in an unevaluated form and then evaluates this form each
+time the left-hand side is used.
+
+There are some cases where "=" is appropriate. Usually, though, ":="
+is the right choice.
+
+=== 10 Credits
+
+Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net>
+Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
+Updates by Sam Ravnborg <sam@ravnborg.org>
+Language QA by Jan Engelhardt <jengelh@gmx.de>
+
+=== 11 TODO
+
+- Describe how kbuild supports shipped files with _shipped.
+- Generating offset header files.
+- Add more variables to section 7?
+
+
+
diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt
new file mode 100644
index 0000000..3fb39e0
--- /dev/null
+++ b/Documentation/kbuild/modules.txt
@@ -0,0 +1,541 @@
+Building External Modules
+
+This document describes how to build an out-of-tree kernel module.
+
+=== Table of Contents
+
+ === 1 Introduction
+ === 2 How to Build External Modules
+ --- 2.1 Command Syntax
+ --- 2.2 Options
+ --- 2.3 Targets
+ --- 2.4 Building Separate Files
+ === 3. Creating a Kbuild File for an External Module
+ --- 3.1 Shared Makefile
+ --- 3.2 Separate Kbuild file and Makefile
+ --- 3.3 Binary Blobs
+ --- 3.4 Building Multiple Modules
+ === 4. Include Files
+ --- 4.1 Kernel Includes
+ --- 4.2 Single Subdirectory
+ --- 4.3 Several Subdirectories
+ === 5. Module Installation
+ --- 5.1 INSTALL_MOD_PATH
+ --- 5.2 INSTALL_MOD_DIR
+ === 6. Module Versioning
+ --- 6.1 Symbols From the Kernel (vmlinux + modules)
+ --- 6.2 Symbols and External Modules
+ --- 6.3 Symbols From Another External Module
+ === 7. Tips & Tricks
+ --- 7.1 Testing for CONFIG_FOO_BAR
+
+
+
+=== 1. Introduction
+
+"kbuild" is the build system used by the Linux kernel. Modules must use
+kbuild to stay compatible with changes in the build infrastructure and
+to pick up the right flags to "gcc." Functionality for building modules
+both in-tree and out-of-tree is provided. The method for building
+either is similar, and all modules are initially developed and built
+out-of-tree.
+
+Covered in this document is information aimed at developers interested
+in building out-of-tree (or "external") modules. The author of an
+external module should supply a makefile that hides most of the
+complexity, so one only has to type "make" to build the module. This is
+easily accomplished, and a complete example will be presented in
+section 3.
+
+
+=== 2. How to Build External Modules
+
+To build external modules, you must have a prebuilt kernel available
+that contains the configuration and header files used in the build.
+Also, the kernel must have been built with modules enabled. If you are
+using a distribution kernel, there will be a package for the kernel you
+are running provided by your distribution.
+
+An alternative is to use the "make" target "modules_prepare." This will
+make sure the kernel contains the information required. The target
+exists solely as a simple way to prepare a kernel source tree for
+building external modules.
+
+NOTE: "modules_prepare" will not build Module.symvers even if
+CONFIG_MODVERSIONS is set; therefore, a full kernel build needs to be
+executed to make module versioning work.
+
+--- 2.1 Command Syntax
+
+ The command to build an external module is:
+
+ $ make -C <path_to_kernel_src> M=$PWD
+
+ The kbuild system knows that an external module is being built
+ due to the "M=<dir>" option given in the command.
+
+ To build against the running kernel use:
+
+ $ make -C /lib/modules/`uname -r`/build M=$PWD
+
+ Then to install the module(s) just built, add the target
+ "modules_install" to the command:
+
+ $ make -C /lib/modules/`uname -r`/build M=$PWD modules_install
+
+--- 2.2 Options
+
+ ($KDIR refers to the path of the kernel source directory.)
+
+ make -C $KDIR M=$PWD
+
+ -C $KDIR
+ The directory where the kernel source is located.
+ "make" will actually change to the specified directory
+ when executing and will change back when finished.
+
+ M=$PWD
+ Informs kbuild that an external module is being built.
+ The value given to "M" is the absolute path of the
+ directory where the external module (kbuild file) is
+ located.
+
+--- 2.3 Targets
+
+ When building an external module, only a subset of the "make"
+ targets are available.
+
+ make -C $KDIR M=$PWD [target]
+
+ The default will build the module(s) located in the current
+ directory, so a target does not need to be specified. All
+ output files will also be generated in this directory. No
+ attempts are made to update the kernel source, and it is a
+ precondition that a successful "make" has been executed for the
+ kernel.
+
+ modules
+ The default target for external modules. It has the
+ same functionality as if no target was specified. See
+ description above.
+
+ modules_install
+ Install the external module(s). The default location is
+ /lib/modules/<kernel_release>/extra/, but a prefix may
+ be added with INSTALL_MOD_PATH (discussed in section 5).
+
+ clean
+ Remove all generated files in the module directory only.
+
+ help
+ List the available targets for external modules.
+
+--- 2.4 Building Separate Files
+
+ It is possible to build single files that are part of a module.
+ This works equally well for the kernel, a module, and even for
+ external modules.
+
+ Example (The module foo.ko, consist of bar.o and baz.o):
+ make -C $KDIR M=$PWD bar.lst
+ make -C $KDIR M=$PWD baz.o
+ make -C $KDIR M=$PWD foo.ko
+ make -C $KDIR M=$PWD /
+
+
+=== 3. Creating a Kbuild File for an External Module
+
+In the last section we saw the command to build a module for the
+running kernel. The module is not actually built, however, because a
+build file is required. Contained in this file will be the name of
+the module(s) being built, along with the list of requisite source
+files. The file may be as simple as a single line:
+
+ obj-m := <module_name>.o
+
+The kbuild system will build <module_name>.o from <module_name>.c,
+and, after linking, will result in the kernel module <module_name>.ko.
+The above line can be put in either a "Kbuild" file or a "Makefile."
+When the module is built from multiple sources, an additional line is
+needed listing the files:
+
+ <module_name>-y := <src1>.o <src2>.o ...
+
+NOTE: Further documentation describing the syntax used by kbuild is
+located in Documentation/kbuild/makefiles.txt.
+
+The examples below demonstrate how to create a build file for the
+module 8123.ko, which is built from the following files:
+
+ 8123_if.c
+ 8123_if.h
+ 8123_pci.c
+ 8123_bin.o_shipped <= Binary blob
+
+--- 3.1 Shared Makefile
+
+ An external module always includes a wrapper makefile that
+ supports building the module using "make" with no arguments.
+ This target is not used by kbuild; it is only for convenience.
+ Additional functionality, such as test targets, can be included
+ but should be filtered out from kbuild due to possible name
+ clashes.
+
+ Example 1:
+ --> filename: Makefile
+ ifneq ($(KERNELRELEASE),)
+ # kbuild part of makefile
+ obj-m := 8123.o
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ else
+ # normal makefile
+ KDIR ?= /lib/modules/`uname -r`/build
+
+ default:
+ $(MAKE) -C $(KDIR) M=$$PWD
+
+ # Module specific targets
+ genbin:
+ echo "X" > 8123_bin.o_shipped
+
+ endif
+
+ The check for KERNELRELEASE is used to separate the two parts
+ of the makefile. In the example, kbuild will only see the two
+ assignments, whereas "make" will see everything except these
+ two assignments. This is due to two passes made on the file:
+ the first pass is by the "make" instance run on the command
+ line; the second pass is by the kbuild system, which is
+ initiated by the parameterized "make" in the default target.
+
+--- 3.2 Separate Kbuild File and Makefile
+
+ In newer versions of the kernel, kbuild will first look for a
+ file named "Kbuild," and only if that is not found, will it
+ then look for a makefile. Utilizing a "Kbuild" file allows us
+ to split up the makefile from example 1 into two files:
+
+ Example 2:
+ --> filename: Kbuild
+ obj-m := 8123.o
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ --> filename: Makefile
+ KDIR ?= /lib/modules/`uname -r`/build
+
+ default:
+ $(MAKE) -C $(KDIR) M=$$PWD
+
+ # Module specific targets
+ genbin:
+ echo "X" > 8123_bin.o_shipped
+
+ The split in example 2 is questionable due to the simplicity of
+ each file; however, some external modules use makefiles
+ consisting of several hundred lines, and here it really pays
+ off to separate the kbuild part from the rest.
+
+ The next example shows a backward compatible version.
+
+ Example 3:
+ --> filename: Kbuild
+ obj-m := 8123.o
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ --> filename: Makefile
+ ifneq ($(KERNELRELEASE),)
+ # kbuild part of makefile
+ include Kbuild
+
+ else
+ # normal makefile
+ KDIR ?= /lib/modules/`uname -r`/build
+
+ default:
+ $(MAKE) -C $(KDIR) M=$$PWD
+
+ # Module specific targets
+ genbin:
+ echo "X" > 8123_bin.o_shipped
+
+ endif
+
+ Here the "Kbuild" file is included from the makefile. This
+ allows an older version of kbuild, which only knows of
+ makefiles, to be used when the "make" and kbuild parts are
+ split into separate files.
+
+--- 3.3 Binary Blobs
+
+ Some external modules need to include an object file as a blob.
+ kbuild has support for this, but requires the blob file to be
+ named <filename>_shipped. When the kbuild rules kick in, a copy
+ of <filename>_shipped is created with _shipped stripped off,
+ giving us <filename>. This shortened filename can be used in
+ the assignment to the module.
+
+ Throughout this section, 8123_bin.o_shipped has been used to
+ build the kernel module 8123.ko; it has been included as
+ 8123_bin.o.
+
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ Although there is no distinction between the ordinary source
+ files and the binary file, kbuild will pick up different rules
+ when creating the object file for the module.
+
+--- 3.4 Building Multiple Modules
+
+ kbuild supports building multiple modules with a single build
+ file. For example, if you wanted to build two modules, foo.ko
+ and bar.ko, the kbuild lines would be:
+
+ obj-m := foo.o bar.o
+ foo-y := <foo_srcs>
+ bar-y := <bar_srcs>
+
+ It is that simple!
+
+
+=== 4. Include Files
+
+Within the kernel, header files are kept in standard locations
+according to the following rule:
+
+ * If the header file only describes the internal interface of a
+ module, then the file is placed in the same directory as the
+ source files.
+ * If the header file describes an interface used by other parts
+ of the kernel that are located in different directories, then
+ the file is placed in include/linux/.
+
+ NOTE: 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/$(ARCH)/include/.
+
+--- 4.1 Kernel Includes
+
+ To include a header file located under include/linux/, simply
+ use:
+
+ #include <linux/module.h>
+
+ kbuild will add options to "gcc" so the relevant directories
+ are searched.
+
+--- 4.2 Single Subdirectory
+
+ External modules tend to place header files in a separate
+ include/ directory where their source is located, although this
+ is not the usual kernel style. To inform kbuild of the
+ directory, use either ccflags-y or CFLAGS_<filename>.o.
+
+ Using the example from section 3, if we moved 8123_if.h to a
+ subdirectory named include, the resulting kbuild file would
+ look like:
+
+ --> filename: Kbuild
+ obj-m := 8123.o
+
+ ccflags-y := -Iinclude
+ 8123-y := 8123_if.o 8123_pci.o 8123_bin.o
+
+ Note that in the assignment there is no space between -I and
+ the path. This is a limitation of kbuild: there must be no
+ space present.
+
+--- 4.3 Several Subdirectories
+
+ kbuild can handle files that are spread over several directories.
+ Consider the following example:
+
+ .
+ |__ src
+ | |__ complex_main.c
+ | |__ hal
+ | |__ hardwareif.c
+ | |__ include
+ | |__ hardwareif.h
+ |__ include
+ |__ complex.h
+
+ To build the module complex.ko, we then need the following
+ kbuild file:
+
+ --> filename: Kbuild
+ obj-m := complex.o
+ complex-y := src/complex_main.o
+ complex-y += src/hal/hardwareif.o
+
+ ccflags-y := -I$(src)/include
+ ccflags-y += -I$(src)/src/hal/include
+
+ As you can see, kbuild knows how to handle object files located
+ in other directories. The trick is to specify the directory
+ relative to the kbuild file's location. That being said, this
+ is NOT recommended practice.
+
+ For the header files, kbuild must be explicitly told where to
+ look. When kbuild executes, the current directory is always the
+ root of the kernel tree (the argument to "-C") and therefore an
+ absolute path is needed. $(src) provides the absolute path by
+ pointing to the directory where the currently executing kbuild
+ file is located.
+
+
+=== 5. Module Installation
+
+Modules which are included in the kernel are installed in the
+directory:
+
+ /lib/modules/$(KERNELRELEASE)/kernel/
+
+And external modules are installed in:
+
+ /lib/modules/$(KERNELRELEASE)/extra/
+
+--- 5.1 INSTALL_MOD_PATH
+
+ Above are the default directories but as always some level of
+ customization is possible. A prefix can be added to the
+ installation path using the variable INSTALL_MOD_PATH:
+
+ $ make INSTALL_MOD_PATH=/frodo modules_install
+ => Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel/
+
+ INSTALL_MOD_PATH may be set as an ordinary shell variable or,
+ as shown above, can be specified on the command line when
+ calling "make." This has effect when installing both in-tree
+ and out-of-tree modules.
+
+--- 5.2 INSTALL_MOD_DIR
+
+ External modules are by default installed to a directory under
+ /lib/modules/$(KERNELRELEASE)/extra/, but you may wish to
+ locate modules for a specific functionality in a separate
+ directory. For this purpose, use INSTALL_MOD_DIR to specify an
+ alternative name to "extra."
+
+ $ make INSTALL_MOD_DIR=gandalf -C $KDIR \
+ M=$PWD modules_install
+ => Install dir: /lib/modules/$(KERNELRELEASE)/gandalf/
+
+
+=== 6. Module Versioning
+
+Module versioning is enabled by the CONFIG_MODVERSIONS tag, and is used
+as a simple ABI consistency check. A CRC value of the full prototype
+for an exported symbol is created. When a module is loaded/used, the
+CRC values contained in the kernel are compared with similar values in
+the module; if they are not equal, the kernel refuses to load the
+module.
+
+Module.symvers contains a list of all exported symbols from a kernel
+build.
+
+--- 6.1 Symbols From the Kernel (vmlinux + modules)
+
+ During a kernel build, a file named Module.symvers will be
+ generated. Module.symvers contains all exported symbols from
+ the kernel and compiled modules. For each symbol, the
+ corresponding CRC value is also stored.
+
+ The syntax of the Module.symvers file is:
+ <CRC> <Symbol> <module>
+
+ 0x2d036834 scsi_remove_host drivers/scsi/scsi_mod
+
+ For a kernel build without CONFIG_MODVERSIONS enabled, the CRC
+ would read 0x00000000.
+
+ Module.symvers serves two purposes:
+ 1) It lists all exported symbols from vmlinux and all modules.
+ 2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
+
+--- 6.2 Symbols and External Modules
+
+ When building an external module, the build system needs access
+ to the symbols from the kernel to check if all external symbols
+ are defined. This is done in the MODPOST step. modpost obtains
+ the symbols by reading Module.symvers from the kernel source
+ tree. If a Module.symvers file is present in the directory
+ where the external module is being built, this file will be
+ read too. During the MODPOST step, a new Module.symvers file
+ will be written containing all exported symbols that were not
+ defined in the kernel.
+
+--- 6.3 Symbols From Another External Module
+
+ Sometimes, an external module uses exported symbols from
+ another external module. kbuild needs to have full knowledge of
+ all symbols to avoid spitting out warnings about undefined
+ symbols. Three solutions exist for this situation.
+
+ NOTE: The method with a top-level kbuild file is recommended
+ but may be impractical in certain situations.
+
+ Use a top-level kbuild file
+ If you have two modules, foo.ko and bar.ko, where
+ foo.ko needs symbols from bar.ko, you can use a
+ common top-level kbuild file so both modules are
+ compiled in the same build. Consider the following
+ directory layout:
+
+ ./foo/ <= contains foo.ko
+ ./bar/ <= contains bar.ko
+
+ The top-level kbuild file would then look like:
+
+ #./Kbuild (or ./Makefile):
+ obj-y := foo/ bar/
+
+ And executing
+
+ $ make -C $KDIR M=$PWD
+
+ will then do the expected and compile both modules with
+ full knowledge of symbols from either module.
+
+ Use an extra Module.symvers file
+ When an external module is built, a Module.symvers file
+ is generated containing all exported symbols which are
+ not defined in the kernel. To get access to symbols
+ from bar.ko, copy the Module.symvers file from the
+ compilation of bar.ko to the directory where foo.ko is
+ built. During the module build, kbuild will read the
+ Module.symvers file in the directory of the external
+ module, and when the build is finished, a new
+ Module.symvers file is created containing the sum of
+ all symbols defined and not part of the kernel.
+
+ Use "make" variable KBUILD_EXTRA_SYMBOLS
+ If it is impractical to copy Module.symvers from
+ another module, you can assign a space separated list
+ of files to KBUILD_EXTRA_SYMBOLS in your build file.
+ These files will be loaded by modpost during the
+ initialization of its symbol tables.
+
+
+=== 7. Tips & Tricks
+
+--- 7.1 Testing for CONFIG_FOO_BAR
+
+ Modules often need to check for certain CONFIG_ options to
+ decide if a specific feature is included in the module. In
+ kbuild this is done by referencing the CONFIG_ variable
+ directly.
+
+ #fs/ext2/Makefile
+ obj-$(CONFIG_EXT2_FS) += ext2.o
+
+ ext2-y := balloc.o bitmap.o dir.o
+ ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
+
+ External modules have traditionally used "grep" to check for
+ specific CONFIG_ settings directly in .config. This usage is
+ broken. As introduced before, external modules should use
+ kbuild for building and can therefore use the same methods as
+ in-tree modules when testing for CONFIG_ definitions.
+