Update Linux to v5.4.2
Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/Documentation/kbuild/00-INDEX b/Documentation/kbuild/00-INDEX
deleted file mode 100644
index 8c5e6aa..0000000
--- a/Documentation/kbuild/00-INDEX
+++ /dev/null
@@ -1,14 +0,0 @@
-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/headers_install.txt b/Documentation/kbuild/headers_install.rst
similarity index 79%
rename from Documentation/kbuild/headers_install.txt
rename to Documentation/kbuild/headers_install.rst
index f0153ad..f6c6b74 100644
--- a/Documentation/kbuild/headers_install.txt
+++ b/Documentation/kbuild/headers_install.rst
@@ -1,3 +1,4 @@
+=============================================
Exporting kernel headers for use by userspace
=============================================
@@ -22,14 +23,14 @@
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:
+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:
+the command::
ls -d include/asm-* | sed 's/.*-//'
@@ -39,12 +40,5 @@
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/index.rst b/Documentation/kbuild/index.rst
new file mode 100644
index 0000000..0f144fa
--- /dev/null
+++ b/Documentation/kbuild/index.rst
@@ -0,0 +1,28 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+Kernel Build System
+===================
+
+.. toctree::
+ :maxdepth: 1
+
+ kconfig-language
+ kconfig-macro-language
+
+ kbuild
+ kconfig
+ makefiles
+ modules
+
+ headers_install
+
+ issues
+ reproducible-builds
+
+.. only:: subproject and html
+
+ Indices
+ =======
+
+ * :ref:`genindex`
diff --git a/Documentation/kbuild/issues.rst b/Documentation/kbuild/issues.rst
new file mode 100644
index 0000000..bdab01f
--- /dev/null
+++ b/Documentation/kbuild/issues.rst
@@ -0,0 +1,15 @@
+================
+Recursion issues
+================
+
+issue #1
+--------
+
+.. literalinclude:: Kconfig.recursion-issue-01
+ :language: kconfig
+
+issue #2
+--------
+
+.. literalinclude:: Kconfig.recursion-issue-02
+ :language: kconfig
diff --git a/Documentation/kbuild/kbuild.txt b/Documentation/kbuild/kbuild.rst
similarity index 61%
rename from Documentation/kbuild/kbuild.txt
rename to Documentation/kbuild/kbuild.rst
index 8390c36..f1e5dce 100644
--- a/Documentation/kbuild/kbuild.txt
+++ b/Documentation/kbuild/kbuild.rst
@@ -1,101 +1,121 @@
+======
+Kbuild
+======
+
+
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.
+modules.builtin.modinfo
+-----------------------
+This file contains modinfo from all modules that are built into the kernel.
+Unlike modinfo of a separate module, all fields are prefixed with module name.
+
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).
+-------------
+Additional assembler options for modules.
AFLAGS_KERNEL
---------------------------------------------------
-Additional options for $(AS) when used for assembler
-code for code that is compiled as built-in.
+-------------
+Additional assembler options for 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.
HOSTCFLAGS
---------------------------------------------------
+----------
Additional flags to be passed to $(HOSTCC) when building host programs.
HOSTCXXFLAGS
---------------------------------------------------
+------------
Additional flags to be passed to $(HOSTCXX) when building host programs.
HOSTLDFLAGS
---------------------------------------------------
+-----------
Additional flags to be passed when linking host programs.
HOSTLDLIBS
---------------------------------------------------
+----------
Additional libraries to link against when building host programs.
KBUILD_KCONFIG
---------------------------------------------------
+--------------
Set the top-level Kconfig file to the value of this environment
variable. The default name is "Kconfig".
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.
+
+Setting "M=..." takes precedence over KBUILD_EXTMOD.
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_EXTRA_WARN
+-----------------
+Specify the extra build checks. The same value can be assigned by passing
+W=... from the command line.
+
+See `make help` for the list of the supported values.
+
+Setting "W=..." takes precedence over KBUILD_EXTRA_WARN.
+
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.
@@ -103,44 +123,49 @@
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
-sh: sh for 32 bit, sh64 for 64 bit
-sparc: sparc32 for 32 bit, sparc64 for 64 bit
+
+- x86: i386 for 32 bit, x86_64 for 64 bit
+- sh: sh for 32 bit, sh64 for 64 bit
+- sparc: sparc32 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:
+
+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)
+
+ - $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.
@@ -149,32 +174,33 @@
specify a custom installer when cross compiling a kernel.
MODLIB
---------------------------------------------------
+------
Specify where to install modules.
-The default value is:
+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_HDR_PATH
---------------------------------------------------
+----------------
INSTALL_HDR_PATH specifies where to install user space headers when
executing "make headers_*".
-The default value is:
+
+The default value is::
$(objtree)/usr
@@ -183,71 +209,56 @@
The value can be overridden in which case the default value is ignored.
-KBUILD_SIGN_PIN
+KBUILD_ABS_SRCTREE
--------------------------------------------------
+Kbuild uses a relative path to point to the tree when possible. For instance,
+when building in the source tree, the source tree path is '.'
+
+Setting this flag requests Kbuild to use absolute path to the source tree.
+There are some useful cases to do so, like when generating tag files with
+absolute path entries etc.
+
+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.:
+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.:
+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_LIBS
---------------------------------------------------
-All .a "lib" files for vmlinux.
-KBUILD_VMLINUX_INIT, KBUILD_VMLINUX_MAIN, and KBUILD_VMLINUX_LIBS together
-specify all the object files used to link vmlinux.
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.rst
similarity index 84%
rename from Documentation/kbuild/kconfig-language.txt
rename to Documentation/kbuild/kconfig-language.rst
index 864e740..74bef19 100644
--- a/Documentation/kbuild/kconfig-language.txt
+++ b/Documentation/kbuild/kconfig-language.rst
@@ -1,8 +1,12 @@
+================
+Kconfig Language
+================
+
Introduction
------------
The configuration database is a collection of configuration options
-organized in a tree structure:
+organized in a tree structure::
+- Code maturity level options
| +- Prompt for development and/or incomplete code/drivers
@@ -25,9 +29,9 @@
------------
Most entries define a config option; all other entries help to organize
-them. A single configuration option is defined like this:
+them. A single configuration option is defined like this::
-config MODVERSIONS
+ config MODVERSIONS
bool "Set version information on all module symbols"
depends on MODULES
help
@@ -49,22 +53,27 @@
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:
+ are equivalent::
bool "Networking support"
- and
+
+ 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
@@ -98,25 +107,31 @@
d) Hardware or infrastructure that everybody expects, such as CONFIG_NET
or CONFIG_BLOCK. These are rare exceptions.
-- type definition + default value:
+- 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:
+ accept an "if" expression), so these two examples are equivalent::
bool "foo" if BAR
default y if BAR
- and
+
+ 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
@@ -124,6 +139,7 @@
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.
@@ -135,34 +151,38 @@
the illegal configurations all over.
- weak reverse dependencies: "imply" <symbol> ["if" <expr>]
+
This is similar to "select" as it enforces a lower limit on another
symbol except that the "implied" symbol's value may still be set to n
from a direct dependency or with a visible prompt.
- Given the following example:
+ Given the following example::
- config FOO
+ config FOO
tristate
imply BAZ
- config BAZ
+ config BAZ
tristate
depends on BAR
The following values are possible:
+ === === ============= ==============
FOO BAR BAZ's default choice for BAZ
- --- --- ------------- --------------
+ === === ============= ==============
n y n N/m/y
m y m M/y/n
y y y Y/n
y n * N
+ === === ============= ==============
This is useful e.g. with multiple drivers that want to indicate their
ability to hook into a secondary subsystem while allowing the user to
configure that subsystem out without also having to unset these drivers.
- 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
@@ -170,12 +190,14 @@
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.
@@ -184,6 +206,7 @@
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:
@@ -208,9 +231,9 @@
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:
+module state. Dependency expressions have the following syntax::
-<expr> ::= <symbol> (1)
+ <expr> ::= <symbol> (1)
<symbol> '=' <symbol> (2)
<symbol> '!=' <symbol> (3)
<symbol1> '<' <symbol2> (4)
@@ -222,7 +245,7 @@
<expr> '&&' <expr> (7)
<expr> '||' <expr> (8)
-Expressions are listed in decreasing order of precedence.
+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
@@ -255,15 +278,15 @@
--------------
The position of a menu entry in the tree is determined in two ways. First
-it can be specified explicitly:
+it can be specified explicitly::
-menu "Network device support"
+ menu "Network device support"
depends on NET
-config NETDEVICES
+ config NETDEVICES
...
-endmenu
+ endmenu
All entries within the "menu" ... "endmenu" block become a submenu of
"Network device support". All subentries inherit the dependencies from
@@ -275,17 +298,18 @@
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
+- 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
+ config MODVERSIONS
bool "Set version information on all module symbols"
depends on MODULES
-comment "module support disabled"
+ comment "module support disabled"
depends on !MODULES
MODVERSIONS directly depends on MODULES, this means it's only visible if
@@ -299,6 +323,7 @@
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
@@ -306,9 +331,10 @@
- menu/endmenu
- if/endif
- source
+
The first five also start the definition of a menu entry.
-config:
+config::
"config" <symbol>
<config options>
@@ -316,7 +342,8 @@
This defines a config symbol <symbol> and accepts any of above
attributes as options.
-menuconfig:
+menuconfig::
+
"menuconfig" <symbol>
<config options>
@@ -325,43 +352,43 @@
separate list of options. To make sure all the suboptions will really
show up under the menuconfig entry and not outside of it, every item
from the <config options> list must depend on the menuconfig symbol.
-In practice, this is achieved by using one of the next two constructs:
+In practice, this is achieved by using one of the next two constructs::
-(1):
-menuconfig M
-if M
- config C1
- config C2
-endif
+ (1):
+ menuconfig M
+ if M
+ config C1
+ config C2
+ endif
-(2):
-menuconfig M
-config C1
- depends on M
-config C2
- depends on M
+ (2):
+ menuconfig M
+ config C1
+ depends on M
+ config C2
+ depends on M
In the following examples (3) and (4), C1 and C2 still have the M
dependency, but will not appear under menuconfig M anymore, because
-of C0, which doesn't depend on M:
+of C0, which doesn't depend on M::
-(3):
-menuconfig M
- config C0
-if M
- config C1
- config C2
-endif
+ (3):
+ menuconfig M
+ config C0
+ if M
+ config C1
+ config C2
+ endif
-(4):
-menuconfig M
-config C0
-config C1
- depends on M
-config C2
- depends on M
+ (4):
+ menuconfig M
+ config C0
+ config C1
+ depends on M
+ config C2
+ depends on M
-choices:
+choices::
"choice" [symbol]
<choice options>
@@ -387,7 +414,7 @@
then you may define the same choice (i.e. with the same entries) in another
place.
-comment:
+comment::
"comment" <prompt>
<comment options>
@@ -396,7 +423,7 @@
configuration process and is also echoed to the output files. The only
possible options are dependencies.
-menu:
+menu::
"menu" <prompt>
<menu options>
@@ -407,7 +434,7 @@
information. The only possible options are dependencies and "visible"
attributes.
-if:
+if::
"if" <expr>
<if block>
@@ -416,13 +443,13 @@
This defines an if block. The dependency expression <expr> is appended
to all enclosed menu entries.
-source:
+source::
"source" <prompt>
This reads the specified configuration file. This file is always parsed.
-mainmenu:
+mainmenu::
"mainmenu" <prompt>
@@ -452,20 +479,21 @@
architectures.
An example is the generic IOMAP functionality.
-We would in lib/Kconfig see:
+We would in lib/Kconfig see::
-# Generic IOMAP is used to ...
-config HAVE_GENERIC_IOMAP
+ # Generic IOMAP is used to ...
+ config HAVE_GENERIC_IOMAP
-config GENERIC_IOMAP
+ config GENERIC_IOMAP
depends on HAVE_GENERIC_IOMAP && FOO
-And in lib/Makefile we would see:
-obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
+And in lib/Makefile we would see::
-For each architecture using the generic IOMAP functionality we would see:
+ obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
-config X86
+For each architecture using the generic IOMAP functionality we would see::
+
+ config X86
select ...
select HAVE_GENERIC_IOMAP
select ...
@@ -484,25 +512,25 @@
There are several features that need compiler support. The recommended way
to describe the dependency on the compiler feature is to use "depends on"
-followed by a test macro.
+followed by a test macro::
-config STACKPROTECTOR
+ config STACKPROTECTOR
bool "Stack Protector buffer overflow detection"
depends on $(cc-option,-fstack-protector)
...
If you need to expose a compiler capability to makefiles and/or C source files,
-CC_HAS_ is the recommended prefix for the config option.
+`CC_HAS_` is the recommended prefix for the config option::
-config CC_HAS_STACKPROTECTOR_NONE
+ config CC_HAS_STACKPROTECTOR_NONE
def_bool $(cc-option,-fno-stack-protector)
Build as module only
~~~~~~~~~~~~~~~~~~~~
To restrict a component build to module-only, qualify its config symbol
-with "depends on m". E.g.:
+with "depends on m". E.g.::
-config FOO
+ config FOO
depends on BAR && m
limits FOO to module (=m) or disabled (=n).
@@ -529,18 +557,18 @@
Read: Documentation/kbuild/Kconfig.recursion-issue-01
-Test with:
+Test with::
-make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
+ make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
Cumulative Kconfig recursive issue
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Read: Documentation/kbuild/Kconfig.recursion-issue-02
-Test with:
+Test with::
-make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
+ make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
Practical solutions to kconfig recursive issue
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -551,7 +579,9 @@
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
@@ -566,8 +596,9 @@
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
@@ -590,6 +621,7 @@
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.
@@ -616,11 +648,11 @@
~~~~~~~~~~~~~~~~~~~~
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].
+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 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
@@ -628,42 +660,42 @@
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).
+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
+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].
+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
+.. [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
+Although SAT solvers [4]_ 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:
+boolean formulas and run a SAT solver on it [5]_. Another known related project
+is CADOS [6]_ (former VAMOS [7]_) and the tools, mainly undertaker [8]_, which
+has been introduced first with [9]_. 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
+.. [4] http://www.cs.cornell.edu/~sabhar/chapters/SATSolvers-KR-Handbook.pdf
+.. [5] http://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
+.. [6] https://cados.cs.fau.de
+.. [7] https://vamos.cs.fau.de
+.. [8] https://undertaker.cs.fau.de
+.. [9] https://www4.cs.fau.de/Publications/2011/tartler_11_eurosys.pdf
diff --git a/Documentation/kbuild/kconfig-macro-language.txt b/Documentation/kbuild/kconfig-macro-language.rst
similarity index 93%
rename from Documentation/kbuild/kconfig-macro-language.txt
rename to Documentation/kbuild/kconfig-macro-language.rst
index 07da2ea..35b3263 100644
--- a/Documentation/kbuild/kconfig-macro-language.txt
+++ b/Documentation/kbuild/kconfig-macro-language.rst
@@ -1,3 +1,7 @@
+======================
+Kconfig macro language
+======================
+
Concept
-------
@@ -7,7 +11,7 @@
substitution.
There is clear distinction between the two language stages. For example, you
-can write a makefile like follows:
+can write a makefile like follows::
APP := foo
SRC := foo.c
@@ -17,7 +21,7 @@
$(CC) -o $(APP) $(SRC)
The macro language replaces the variable references with their expanded form,
-and handles as if the source file were input like follows:
+and handles as if the source file were input like follows::
foo: foo.c
gcc -o foo foo.c
@@ -26,7 +30,7 @@
updated.
The idea is quite similar in Kconfig - it is possible to describe a Kconfig
-file like this:
+file like this::
CC := gcc
@@ -34,7 +38,7 @@
def_bool $(shell, $(srctree)/scripts/gcc-check-foo.sh $(CC))
The macro language in Kconfig processes the source file into the following
-intermediate:
+intermediate::
config CC_HAS_FOO
def_bool y
@@ -69,7 +73,7 @@
side was originally defined as a simple variable. Otherwise, its evaluation is
deferred.
-The variable reference can take parameters, in the following form:
+The variable reference can take parameters, in the following form::
$(name,arg1,arg2,arg3)
@@ -141,7 +145,7 @@
Kconfig adopts Make-like macro language, but the function call syntax is
slightly different.
-A function call in Make looks like this:
+A function call in Make looks like this::
$(func-name arg1,arg2,arg3)
@@ -149,14 +153,14 @@
whitespace. Then, leading whitespaces are trimmed from the first argument,
while whitespaces in the other arguments are kept. You need to use a kind of
trick to start the first parameter with spaces. For example, if you want
-to make "info" function print " hello", you can write like follows:
+to make "info" function print " hello", you can write like follows::
empty :=
space := $(empty) $(empty)
$(info $(space)$(space)hello)
Kconfig uses only commas for delimiters, and keeps all whitespaces in the
-function call. Some people prefer putting a space after each comma delimiter:
+function call. Some people prefer putting a space after each comma delimiter::
$(func-name, arg1, arg2, arg3)
@@ -166,7 +170,7 @@
replaces ".c" with " .o".
In Make, a user-defined function is referenced by using a built-in function,
-'call', like this:
+'call', like this::
$(call my-func,arg1,arg2,arg3)
@@ -179,12 +183,12 @@
this is _useful_ inconsistency.
In Kconfig, for simpler implementation and grammatical consistency, commas that
-appear in the $( ) context are always delimiters. It means
+appear in the $( ) context are always delimiters. It means::
$(shell, echo hello, world)
is an error because it is passing two parameters where the 'shell' function
-accepts only one. To pass commas in arguments, you can use the following trick:
+accepts only one. To pass commas in arguments, you can use the following trick::
comma := ,
$(shell, echo hello$(comma) world)
@@ -195,7 +199,7 @@
A variable (or function) cannot be expanded across tokens. So, you cannot use
a variable as a shorthand for an expression that consists of multiple tokens.
-The following works:
+The following works::
RANGE_MIN := 1
RANGE_MAX := 3
@@ -204,7 +208,7 @@
int "foo"
range $(RANGE_MIN) $(RANGE_MAX)
-But, the following does not work:
+But, the following does not work::
RANGES := 1 3
@@ -213,7 +217,7 @@
range $(RANGES)
A variable cannot be expanded to any keyword in Kconfig. The following does
-not work:
+not work::
MY_TYPE := tristate
@@ -223,7 +227,8 @@
Obviously from the design, $(shell command) is expanded in the textual
substitution phase. You cannot pass symbols to the 'shell' function.
-The following does not work as expected.
+
+The following does not work as expected::
config ENDIAN_FLAG
string
@@ -234,7 +239,7 @@
def_bool $(shell $(srctree)/scripts/gcc-check-flag ENDIAN_FLAG)
Instead, you can do like follows so that any function call is statically
-expanded.
+expanded::
config CC_HAS_ENDIAN_FLAG
bool
diff --git a/Documentation/kbuild/kconfig.txt b/Documentation/kbuild/kconfig.rst
similarity index 74%
rename from Documentation/kbuild/kconfig.txt
rename to Documentation/kbuild/kconfig.rst
index 68c8291..a9a855f 100644
--- a/Documentation/kbuild/kconfig.txt
+++ b/Documentation/kbuild/kconfig.rst
@@ -1,4 +1,8 @@
-This file contains some assistance for using "make *config".
+===================
+Kconfig make config
+===================
+
+This file contains some assistance for using `make *config`.
Use "make help" to list all of the possible configuration targets.
@@ -6,9 +10,8 @@
programs also have embedded help text. Be sure to check that 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
@@ -17,51 +20,55 @@
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, use
+To see a list of new config symbols, use::
cp user/some/old.config .config
make listnewconfig
and the config program will list any new symbols, one per line.
-Alternatively, you can use the brute force method:
+Alternatively, you can use the brute force method::
make oldconfig
scripts/diffconfig .config.old .config | less
-______________________________________________________________________
-Environment variables for '*config'
+----------------------------------------------------------------------
+
+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
+`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_".
+`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"
+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
+(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.
@@ -74,43 +81,55 @@
(usually a subset of all) preset config symbols. These variable
settings are still subject to normal dependency checks.
-Examples:
+Examples::
+
KCONFIG_ALLCONFIG=custom-notebook.config make allnoconfig
-or
+
+or::
+
KCONFIG_ALLCONFIG=mini.config make allnoconfig
-or
+
+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:
+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'
@@ -121,34 +140,36 @@
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 'syncconfig'
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
@@ -158,7 +179,8 @@
names, so you have to know something close to what you are
looking for.
- Example:
+ Example::
+
/hotplug
This lists all config symbols that contain "hotplug",
e.g., HOTPLUG_CPU, MEMORY_HOTPLUG.
@@ -166,48 +188,55 @@
For search help, enter / followed by 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
+ 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:
+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)
+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:
+Example::
+
make MENUCONFIG_MODE=single_menu menuconfig
+----------------------------------------------------------------------
-======================================================================
nconfig
---------------------------------------------------
+-------
nconfig is an alternate text-based configurator. It lists function
keys across the bottom of the terminal (window) that execute commands.
@@ -231,16 +260,17 @@
given string or regular expression (regex).
NCONFIG_MODE
---------------------------------------------------
+------------
This mode shows all sub-menus in one large tree.
-Example:
+Example::
+
make NCONFIG_MODE=single_menu nconfig
+----------------------------------------------------------------------
-======================================================================
xconfig
---------------------------------------------------
+-------
Searching in xconfig:
@@ -248,9 +278,12 @@
names, so you have to know something close to what you are
looking for.
- Example:
+ Example::
+
Ctrl-F hotplug
- or
+
+ or::
+
Menu: File, Search, hotplug
lists all config symbol entries that contain "hotplug" in
@@ -260,13 +293,12 @@
to return to the main menu.
-======================================================================
+----------------------------------------------------------------------
+
gconfig
---------------------------------------------------
+-------
Searching in gconfig:
There is no search command in gconfig. However, gconfig does
have several different viewing choices, modes, and options.
-
-###
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.rst
similarity index 80%
rename from Documentation/kbuild/makefiles.txt
rename to Documentation/kbuild/makefiles.rst
index 7b6a2b2..b89c881 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.rst
@@ -1,8 +1,10 @@
+======================
Linux Kernel Makefiles
+======================
This document describes the Linux kernel Makefiles.
-=== Table of Contents
+.. Table of Contents
=== 1 Overview
=== 2 Who does what
@@ -54,9 +56,10 @@
=== 10 Credits
=== 11 TODO
-=== 1 Overview
+1 Overview
+==========
-The Makefiles have five parts:
+The Makefiles have five parts::
Makefile the top Makefile.
.config the kernel configuration file.
@@ -85,7 +88,8 @@
are used to build the kernel based on the kbuild makefiles.
-=== 2 Who does what
+2 Who does what
+===============
People have four different relationships with the kernel Makefiles.
@@ -110,7 +114,8 @@
This document is aimed towards normal developers and arch developers.
-=== 3 The kbuild files
+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
@@ -122,7 +127,8 @@
Section 3.1 "Goal definitions" is a quick intro, further chapters provide
more details, with real examples.
---- 3.1 Goal definitions
+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
@@ -130,7 +136,8 @@
The most simple kbuild makefile contains one line:
- Example:
+ Example::
+
obj-y += foo.o
This tells kbuild that there is one object in that directory, named
@@ -139,14 +146,16 @@
If foo.o shall be built as a module, the variable obj-m is used.
Therefore the following pattern is often used:
- Example:
+ 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
+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
@@ -154,13 +163,8 @@
Kbuild compiles all the $(obj-y) files. It then calls
"$(AR) rcSTP" to merge these files into one built-in.a file.
- This is a thin archive without a symbol table, which makes it
- unsuitable as a linker input.
-
- The scripts/link-vmlinux.sh script later makes an aggregate
- built-in.a with "${AR} rcsTP", which creates the thin archive
- with a symbol table and an index, making it a valid input for
- the final vmlinux link passes.
+ This is a thin archive without a symbol table. It will be later
+ linked into vmlinux by scripts/link-vmlinux.sh
The order of files in $(obj-y) is significant. Duplicates in
the lists are allowed: the first instance will be linked into
@@ -172,14 +176,16 @@
order may e.g. change the order in which your SCSI
controllers are detected, and thus your disks are renumbered.
- Example:
+ Example::
+
#drivers/isdn/i4l/Makefile
# Makefile for the kernel ISDN subsystem and device drivers.
# Each configuration option enables a list of files.
obj-$(CONFIG_ISDN_I4L) += isdn.o
obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
---- 3.3 Loadable module goals - obj-m
+3.3 Loadable module goals - obj-m
+---------------------------------
$(obj-m) specifies object files which are built as loadable
kernel modules.
@@ -188,7 +194,8 @@
files. In the case of one source file, the kbuild makefile
simply adds the file to $(obj-m).
- Example:
+ Example::
+
#drivers/isdn/i4l/Makefile
obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
@@ -200,7 +207,8 @@
module from, so you have to tell it by setting a $(<module_name>-y)
variable.
- Example:
+ Example::
+
#drivers/isdn/i4l/Makefile
obj-$(CONFIG_ISDN_I4L) += isdn.o
isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o
@@ -210,10 +218,11 @@
"$(LD) -r" on the list of these files to generate isdn.o.
Due to kbuild recognizing $(<module_name>-y) for composite objects,
- you can use the value of a CONFIG_ symbol to optionally include an
+ you can use the value of a `CONFIG_` symbol to optionally include an
object file as part of a composite object.
- Example:
+ Example::
+
#fs/ext2/Makefile
obj-$(CONFIG_EXT2_FS) += ext2.o
ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \
@@ -230,12 +239,14 @@
kbuild will build an ext2.o file for you out of the individual
parts and then link this into built-in.a, as you would expect.
---- 3.4 Objects which export symbols
+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
+3.5 Library file goals - lib-y
+------------------------------
Objects listed with obj-* are used for modules, or
combined in a built-in.a for that specific directory.
@@ -252,18 +263,21 @@
and to be part of a library. Therefore the same directory
may contain both a built-in.a and a lib.a file.
- Example:
+ 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.
+ Use of lib-y is normally restricted to `lib/` and `arch/*/lib`.
---- 3.6 Descending down in directories
+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
@@ -275,7 +289,8 @@
ext2 lives in a separate directory, and the Makefile present in fs/
tells kbuild to descend down using the following assignment.
- Example:
+ Example::
+
#fs/Makefile
obj-$(CONFIG_EXT2_FS) += ext2/
@@ -286,11 +301,12 @@
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
+ 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'.
+ corresponding `CONFIG_` option is neither 'y' nor 'm'.
---- 3.7 Compilation flags
+3.7 Compilation flags
+---------------------
ccflags-y, asflags-y and ldflags-y
These three flags apply only to the kbuild makefile in which they
@@ -302,7 +318,8 @@
ccflags-y specifies options for compiling with $(CC).
- Example:
+ Example::
+
# drivers/acpi/acpica/Makefile
ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA
ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT
@@ -311,15 +328,17 @@
variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
entire tree.
- asflags-y specifies options for assembling with $(AS).
+ asflags-y specifies assembler options.
- Example:
+ Example::
+
#arch/sparc/kernel/Makefile
asflags-y := -ansi
ldflags-y specifies options for linking with $(LD).
- Example:
+ Example::
+
#arch/cris/boot/compressed/Makefile
ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds
@@ -330,18 +349,19 @@
Options specified using subdir-* are added to the commandline before
the options specified using the non-subdir variants.
- Example:
+ Example::
+
subdir-ccflags-y := -Werror
CFLAGS_$@, 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:
+ Example::
+
# drivers/scsi/Makefile
CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF
CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \
@@ -352,24 +372,28 @@
$(AFLAGS_$@) is a similar feature for source files in assembly
languages.
- Example:
+ 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
+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
+
+ 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
+3.10 Special Rules
+------------------
Special rules are used when the kbuild infrastructure does
not provide the required support. A typical example is
@@ -384,43 +408,47 @@
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.
+ $(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.
+ $(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:
+ 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).
+ This is a special rule, following the normal syntax
+ required by make.
- $(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.
+ 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).
- Example:
+ $(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
+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.
@@ -430,10 +458,11 @@
as-option
as-option is used to check if $(CC) -- when used to compile
- assembler (*.S) files -- supports the given option. An optional
+ assembler (`*.S`) files -- supports the given option. An optional
second option may be specified if the first option is not supported.
- Example:
+ Example::
+
#arch/sh/Makefile
cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),)
@@ -442,31 +471,18 @@
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
+ Note: as-instr-option uses KBUILD_AFLAGS for assembler 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:
+ Example::
+
#arch/x86/Makefile
cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
@@ -480,7 +496,8 @@
cc-option-yn is used to check if gcc supports a given option
and return 'y' if supported, otherwise 'n'.
- Example:
+ Example::
+
#arch/ppc/Makefile
biarch := $(call cc-option-yn, -m32)
aflags-$(biarch) += -a32
@@ -498,35 +515,20 @@
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:
+ 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:
+ Example::
+
#fs/reiserfs/Makefile
ccflags-y := $(call cc-ifversion, -lt, 0402, -O1)
@@ -537,21 +539,6 @@
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 $(CC) in path with
one of the listed prefixes. The first prefix where there exist a
@@ -566,7 +553,8 @@
build (host arch is different from target arch). And if CROSS_COMPILE
is already set then leave it with the old value.
- Example:
+ Example::
+
#arch/m68k/Makefile
ifneq ($(SUBARCH),$(ARCH))
ifeq ($(CROSS_COMPILE),)
@@ -574,7 +562,8 @@
endif
endif
---- 3.12 $(LD) support functions
+3.12 $(LD) support functions
+----------------------------
ld-option
ld-option is used to check if $(LD) supports the supplied option.
@@ -582,12 +571,14 @@
The second argument is an optional option that can be used if the
first option is not supported by $(LD).
- Example:
+ Example::
+
#Makefile
LDFLAGS_vmlinux += $(call ld-option, -X)
-=== 4 Host Program support
+4 Host Program support
+======================
Kbuild supports building executables on the host for use during the
compilation stage.
@@ -601,21 +592,24 @@
or utilise the variable $(always).
Both possibilities are described in the following.
---- 4.1 Simple Host Program
+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:
+ 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
+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
@@ -623,7 +617,8 @@
$(<executable>-objs) lists all objects used to link the final
executable.
- Example:
+ Example::
+
#scripts/lxdialog/Makefile
hostprogs-y := lxdialog
lxdialog-objs := checklist.o lxdialog.o
@@ -631,16 +626,19 @@
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
+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:
+ Example::
+
#scripts/kconfig/Makefile
hostprogs-y := qconf
qconf-cxxobjs := qconf.o
@@ -651,13 +649,15 @@
If qconf is composed of a mixture of .c and .cc files, then an
additional line can be used to identify this.
- Example:
+ Example::
+
#scripts/kconfig/Makefile
hostprogs-y := qconf
qconf-cxxobjs := qconf.o
qconf-objs := check.o
---- 4.4 Controlling compiler options for host programs
+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 $(HOSTCC) passed
@@ -665,27 +665,31 @@
To set flags that will take effect for all host programs created
in that Makefile, use the variable HOST_EXTRACFLAGS.
- Example:
+ Example::
+
#scripts/lxdialog/Makefile
HOST_EXTRACFLAGS += -I/usr/include/ncurses
To set specific flags for a single file the following construction
is used:
- Example:
+ Example::
+
#arch/ppc64/boot/Makefile
HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE)
It is also possible to specify additional options to the linker.
- Example:
+ Example::
+
#scripts/kconfig/Makefile
HOSTLDLIBS_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
+4.5 When host programs are actually built
+-----------------------------------------
Kbuild will only build host-programs when they are referenced
as a prerequisite.
@@ -693,7 +697,8 @@
(1) List the prerequisite explicitly in a special rule.
- Example:
+ Example::
+
#drivers/pci/Makefile
hostprogs-y := gen-devlist
$(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist
@@ -704,11 +709,13 @@
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:
+ Example::
+
#scripts/lxdialog/Makefile
hostprogs-y := lxdialog
always := $(hostprogs-y)
@@ -716,11 +723,13 @@
This will tell kbuild to build lxdialog even if not referenced in
any rule.
---- 4.6 Using hostprogs-$(CONFIG_FOO)
+4.6 Using hostprogs-$(CONFIG_FOO)
+---------------------------------
A typical pattern in a Kbuild file looks like this:
- Example:
+ Example::
+
#scripts/Makefile
hostprogs-$(CONFIG_KALLSYMS) += kallsyms
@@ -730,7 +739,8 @@
like hostprogs-y. But only hostprogs-y is recommended to be used
when no CONFIG symbols are involved.
-=== 5 Kbuild clean infrastructure
+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.
@@ -740,9 +750,11 @@
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 $(clean-files).
+Additional files or directories can be specified in kbuild makefiles by use of
+$(clean-files).
- Example:
+ Example::
+
#lib/Makefile
clean-files := crc32table.h
@@ -750,27 +762,15 @@
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) $(offsets-file)
+To exclude certain files or directories from make clean, use the
+$(no-clean-files) variable.
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:
+ Example::
+
#arch/x86/boot/Makefile
subdir- := compressed/
@@ -780,7 +780,8 @@
To support the clean infrastructure in the Makefiles that build the
final bootimage there is an optional target named archclean:
- Example:
+ Example::
+
#arch/x86/Makefile
archclean:
$(Q)$(MAKE) $(clean)=arch/x86/boot
@@ -796,7 +797,8 @@
Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will
be visited during "make clean".
-=== 6 Architecture Makefiles
+6 Architecture Makefiles
+========================
The top level Makefile sets up the environment and does the preparation,
before starting to descend down in the individual directories.
@@ -807,6 +809,7 @@
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:
@@ -824,37 +827,45 @@
- Preparing initrd images and the like
---- 6.1 Set variables to tweak the build to the architecture
+6.1 Set variables to tweak the build to the architecture
+--------------------------------------------------------
- LDFLAGS Generic $(LD) options
+ LDFLAGS
+ Generic $(LD) options
Flags used for all invocations of the linker.
Often specifying the emulation is sufficient.
- Example:
+ 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_vmlinux Options for $(LD) when linking vmlinux
+ 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:
+ Example::
+
#arch/x86/Makefile
LDFLAGS_vmlinux := -e stext
- OBJCOPYFLAGS objcopy flags
+ 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:
+ Example::
+
#arch/s390/Makefile
OBJCOPYFLAGS := -O binary
@@ -865,30 +876,34 @@
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
+ KBUILD_AFLAGS
+ Assembler flags
Default value - see top level Makefile
Append or modify as required per architecture.
- Example:
+ Example::
+
#arch/sparc64/Makefile
KBUILD_AFLAGS += -m64 -mcpu=ultrasparc
- KBUILD_CFLAGS $(CC) compiler flags
+ KBUILD_CFLAGS
+ $(CC) compiler flags
Default value - see top level Makefile
Append or modify as required per architecture.
Often, the KBUILD_CFLAGS variable depends on the configuration.
- Example:
+ Example::
+
#arch/x86/boot/compressed/Makefile
cflags-$(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:
+ probe supported options::
#arch/x86/Makefile
@@ -904,67 +919,80 @@
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
+ Assembler 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
+ Assembler options specific for modules
$(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that
- are used for $(AS).
+ are used for assembler.
+
From commandline AFLAGS_MODULE shall be used (see kbuild.txt).
- KBUILD_CFLAGS_KERNEL $(CC) options specific for built-in
+ 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
+ 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
+ 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_LDS
- $(KBUILD_ARFLAGS) set by the top level Makefile to "D" (deterministic
- mode) if this option is supported by $(AR).
+ The linker script with full path. Assigned by the top-level Makefile.
- ARCH_CPPFLAGS, ARCH_AFLAGS, ARCH_CFLAGS Overrides the kbuild defaults
+ KBUILD_LDS_MODULE
- 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.
+ The module linker script with full path. Assigned by the top-level
+ Makefile and additionally by the arch Makefile.
+ KBUILD_VMLINUX_OBJS
---- 6.2 Add prerequisites to archheaders:
+ All object files for vmlinux. They are linked to vmlinux in the same
+ order as listed in KBUILD_VMLINUX_OBJS.
+
+ KBUILD_VMLINUX_LIBS
+
+ All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and
+ KBUILD_VMLINUX_LIBS together specify all the object files used to
+ link vmlinux.
+
+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.
+ may be installed into user space by "make header_install".
It is run before "make archprepare" when run on the
architecture itself.
---- 6.3 Add prerequisites to archprepare:
+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:
+ Example::
+
#arch/arm/Makefile
archprepare: maketools
@@ -974,7 +1002,8 @@
generating offset header files.
---- 6.4 List directories to visit when descending
+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
@@ -982,28 +1011,34 @@
machinery is all architecture-independent.
- head-y, init-y, core-y, libs-y, drivers-y, net-y
+ head-y, init-y, core-y, libs-y, drivers-y, net-y
+ $(head-y) lists objects to be linked first in vmlinux.
- $(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.a object file can be
- located.
+ $(libs-y) lists directories where a lib.a archive 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 $(net-y).
+ The rest list directories where a built-in.a object file can be
+ located.
- The top level Makefile defines values for all generic directories,
- and arch/$(ARCH)/Makefile only adds architecture-specific directories.
+ $(init-y) objects will be located after $(head-y).
- Example:
+ 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-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/
---- 6.5 Architecture-specific boot images
+6.5 Architecture-specific boot images
+-------------------------------------
An arch Makefile specifies goals that take the vmlinux file, compress
it, wrap it in bootstrapping code, and copy the resulting files
@@ -1021,7 +1056,8 @@
arch/$(ARCH)/Makefile, and use the full path when calling down
into the arch/$(ARCH)/boot/Makefile.
- Example:
+ Example::
+
#arch/x86/Makefile
boot := arch/x86/boot
bzImage: vmlinux
@@ -1034,7 +1070,8 @@
but executing "make help" will list all relevant targets.
To support this, $(archhelp) must be defined.
- Example:
+ Example::
+
#arch/x86/Makefile
define archhelp
echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)'
@@ -1048,42 +1085,64 @@
Add a new prerequisite to all: to select a default goal different
from vmlinux.
- Example:
+ Example::
+
#arch/x86/Makefile
all: bzImage
When "make" is executed without arguments, bzImage will be built.
---- 6.6 Building non-kbuild targets
+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-*.
+ 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:
+ 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.a.
+ header-test-y
---- 6.7 Commands useful for building a boot image
+ header-test-y specifies headers (`*.h`) in the current directory that
+ should be compile tested to ensure they are self-contained,
+ i.e. compilable as standalone units. If CONFIG_HEADER_TEST is enabled,
+ this builds them as part of extra-y.
- Kbuild provides a few macros that are useful when building a
- boot image.
+ header-test-pattern-y
+
+ This works as a weaker version of header-test-y, and accepts wildcard
+ patterns. The typical usage is::
+
+ header-test-pattern-y += *.h
+
+ This specifies all the files that matches to `*.h` in the current
+ directory, but the files in 'header-test-' are excluded.
+
+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:
+ Usage::
+
target: source(s) FORCE
$(call if_changed,ld/objcopy/gzip/...)
@@ -1101,12 +1160,16 @@
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/...)
+ after the comma)::
- Note: if_changed should not be used more than once per target.
+ target: source(s) FORCE
+
+ **WRONG!** $(call if_changed, ld/objcopy/gzip/...)
+
+ Note:
+ if_changed should not be used more than once per target.
It stores the executed command in a corresponding .cmd
+
file and multiple calls would result in overwrites and
unwanted results when the target is up to date and only the
tests on changed commands trigger execution of commands.
@@ -1114,7 +1177,8 @@
ld
Link target. Often, LDFLAGS_$@ is used to set specific options to ld.
- Example:
+ Example::
+
#arch/x86/boot/Makefile
LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary
LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext
@@ -1128,12 +1192,15 @@
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,
+
+ Note:
+ It is a common mistake to forget the "targets :=" assignment,
resulting in the target file being recompiled for no
obvious reason.
@@ -1145,7 +1212,8 @@
gzip
Compress target. Use maximum compression to compress target.
- Example:
+ Example::
+
#arch/x86/boot/compressed/Makefile
$(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE
$(call if_changed,gzip)
@@ -1156,26 +1224,30 @@
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
+ 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 $(src)/%.dts;
+ A central rule exists to create `$(obj)/%.dtb` from `$(src)/%.dts`;
architecture Makefiles do no need to explicitly write out that rule.
- Example:
+ Example::
+
targets += $(dtb-y)
DTC_FLAGS ?= -p 1024
---- 6.8 Custom kbuild commands
+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
+ two variables to be set::
- Example:
+ quiet_cmd_<command> - what shall be echoed
+ cmd_<command> - the command to execute
+
+ Example::
+
#
quiet_cmd_image = BUILD $@
cmd_image = $(obj)/tools/build $(BUILDFLAGS) \
@@ -1186,9 +1258,9 @@
$(call if_changed,image)
@echo 'Kernel: $@ is ready'
- When updating the $(obj)/bzImage target, the line
+ When updating the $(obj)/bzImage target, the line:
- BUILD arch/x86/boot/bzImage
+ BUILD arch/x86/boot/bzImage
will be displayed with "make KBUILD_VERBOSE=0".
@@ -1199,9 +1271,10 @@
arch/$(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.
+ kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`.
- Example:
+ Example::
+
#arch/x86/kernel/Makefile
always := vmlinux.lds
@@ -1213,17 +1286,19 @@
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.
+ When building the `*.lds` target, kbuild uses the variables::
- The kbuild infrastructure for *lds files is used in several
+ 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
+6.10 Generic header files
+-------------------------
The directory include/asm-generic contains the header files
that may be shared between individual architectures.
@@ -1231,7 +1306,8 @@
to list the file in the Kbuild file.
See "7.2 generic-y" for further info on syntax etc.
---- 6.11 Post-link pass
+6.11 Post-link pass
+-------------------
If the file arch/xxx/Makefile.postlink exists, this makefile
will be invoked for post-link objects (vmlinux and modules.ko)
@@ -1246,15 +1322,17 @@
For example, powerpc uses this to check relocation sanity of
the linked vmlinux file.
-=== 7 Kbuild syntax for exported headers
+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__)
+- drop all sections that are kernel internal (guarded by `ifdef __KERNEL__`)
All headers under include/uapi/, include/generated/uapi/,
arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/
@@ -1264,40 +1342,45 @@
arch/<arch>/include/asm/ to list asm files coming from asm-generic.
See subsequent chapter for the syntax of the Kbuild file.
---- 7.1 no-export-headers
+7.1 no-export-headers
+---------------------
no-export-headers is essentially used by include/uapi/linux/Kbuild to
avoid exporting specific headers (e.g. kvm.h) on architectures that do
not support it. It should be avoided as much as possible.
---- 7.2 generic-y
+7.2 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:
+ 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:
+ file is generated in the directory::
arch/$(ARCH)/include/generated/asm
When a header is exported where the architecture uses
the generic header a similar wrapper is generated as part
- of the set of exported headers in the directory:
+ of the set of exported headers in the directory::
usr/include/asm
The generated wrapper will in both cases look like the following:
- Example: termios.h
+ Example: termios.h::
+
#include <asm-generic/termios.h>
---- 7.3 generated-y
+7.3 generated-y
+---------------
If an architecture generates other header files alongside generic-y
wrappers, generated-y specifies them.
@@ -1305,25 +1388,30 @@
This prevents them being treated as stale asm-generic wrappers and
removed.
- Example:
+ Example::
+
#arch/x86/include/asm/Kbuild
generated-y += syscalls_32.h
---- 7.4 mandatory-y
+7.4 mandatory-y
+---------------
- mandatory-y is essentially used by include/uapi/asm-generic/Kbuild.asm
- to define the minimum set of headers that must be exported in
- include/asm.
+ mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild
+ to define the minimum set of ASM headers that all architectures must have.
+
+ This works like optional generic-y. If a mandatory header is missing
+ in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate
+ a wrapper of the asm-generic one.
The convention is to list one subdir per line and
preferably in alphabetic order.
-=== 8 Kbuild Variables
+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.
@@ -1337,32 +1425,28 @@
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:
+ 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.
@@ -1373,7 +1457,6 @@
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
@@ -1381,7 +1464,8 @@
command.
-=== 9 Makefile language
+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
@@ -1400,18 +1484,17 @@
There are some cases where "=" is appropriate. Usually, though, ":="
is the right choice.
-=== 10 Credits
+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>
+- 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
+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.rst
similarity index 82%
rename from Documentation/kbuild/modules.txt
rename to Documentation/kbuild/modules.rst
index 3fb39e0..774a998 100644
--- a/Documentation/kbuild/modules.txt
+++ b/Documentation/kbuild/modules.rst
@@ -1,8 +1,10 @@
+=========================
Building External Modules
+=========================
This document describes how to build an out-of-tree kernel module.
-=== Table of Contents
+.. Table of Contents
=== 1 Introduction
=== 2 How to Build External Modules
@@ -31,7 +33,8 @@
-=== 1. Introduction
+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
@@ -48,7 +51,8 @@
section 3.
-=== 2. How to Build External Modules
+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.
@@ -65,25 +69,27 @@
CONFIG_MODVERSIONS is set; therefore, a full kernel build needs to be
executed to make module versioning work.
---- 2.1 Command Syntax
+2.1 Command Syntax
+==================
- The command to build an external module is:
+ 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:
+ 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:
+ "modules_install" to the command::
$ make -C /lib/modules/`uname -r`/build M=$PWD modules_install
---- 2.2 Options
+2.2 Options
+===========
($KDIR refers to the path of the kernel source directory.)
@@ -100,7 +106,8 @@
directory where the external module (kbuild file) is
located.
---- 2.3 Targets
+2.3 Targets
+===========
When building an external module, only a subset of the "make"
targets are available.
@@ -130,26 +137,29 @@
help
List the available targets for external modules.
---- 2.4 Building Separate Files
+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):
+ 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 /
+ make -C $KDIR M=$PWD ./
-=== 3. Creating a Kbuild File for an External Module
+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:
+files. The file may be as simple as a single line::
obj-m := <module_name>.o
@@ -157,15 +167,15 @@
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:
+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.
+located in Documentation/kbuild/makefiles.rst.
The examples below demonstrate how to create a build file for the
-module 8123.ko, which is built from the following files:
+module 8123.ko, which is built from the following files::
8123_if.c
8123_if.h
@@ -181,7 +191,8 @@
but should be filtered out from kbuild due to possible name
clashes.
- Example 1:
+ Example 1::
+
--> filename: Makefile
ifneq ($(KERNELRELEASE),)
# kbuild part of makefile
@@ -209,14 +220,16 @@
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
+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:
+ Example 2::
+
--> filename: Kbuild
obj-m := 8123.o
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
@@ -238,7 +251,8 @@
The next example shows a backward compatible version.
- Example 3:
+ Example 3::
+
--> filename: Kbuild
obj-m := 8123.o
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
@@ -266,7 +280,8 @@
makefiles, to be used when the "make" and kbuild parts are
split into separate files.
---- 3.3 Binary Blobs
+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
@@ -277,7 +292,7 @@
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_bin.o::
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
@@ -285,11 +300,12 @@
files and the binary file, kbuild will pick up different rules
when creating the object file for the module.
---- 3.4 Building Multiple Modules
+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:
+ and bar.ko, the kbuild lines would be::
obj-m := foo.o bar.o
foo-y := <foo_srcs>
@@ -298,7 +314,8 @@
It is that simple!
-=== 4. Include Files
+4. Include Files
+================
Within the kernel, header files are kept in standard locations
according to the following rule:
@@ -310,22 +327,25 @@
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/.
+ 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/$(ARCH)/include/.
---- 4.1 Kernel Includes
+4.1 Kernel Includes
+-------------------
To include a header file located under include/linux/, simply
- use:
+ use::
#include <linux/module.h>
kbuild will add options to "gcc" so the relevant directories
are searched.
---- 4.2 Single Subdirectory
+4.2 Single Subdirectory
+-----------------------
External modules tend to place header files in a separate
include/ directory where their source is located, although this
@@ -334,7 +354,7 @@
Using the example from section 3, if we moved 8123_if.h to a
subdirectory named include, the resulting kbuild file would
- look like:
+ look like::
--> filename: Kbuild
obj-m := 8123.o
@@ -346,23 +366,24 @@
the path. This is a limitation of kbuild: there must be no
space present.
---- 4.3 Several Subdirectories
+4.3 Several Subdirectories
+--------------------------
kbuild can handle files that are spread over several directories.
- Consider the following example:
+ Consider the following example::
- .
- |__ src
- | |__ complex_main.c
- | |__ hal
- | |__ hardwareif.c
- | |__ include
- | |__ hardwareif.h
- |__ include
- |__ complex.h
+ .
+ |__ src
+ | |__ complex_main.c
+ | |__ hal
+ | |__ hardwareif.c
+ | |__ include
+ | |__ hardwareif.h
+ |__ include
+ |__ complex.h
To build the module complex.ko, we then need the following
- kbuild file:
+ kbuild file::
--> filename: Kbuild
obj-m := complex.o
@@ -385,7 +406,8 @@
file is located.
-=== 5. Module Installation
+5. Module Installation
+======================
Modules which are included in the kernel are installed in the
directory:
@@ -396,11 +418,12 @@
/lib/modules/$(KERNELRELEASE)/extra/
---- 5.1 INSTALL_MOD_PATH
+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:
+ installation path using the variable INSTALL_MOD_PATH::
$ make INSTALL_MOD_PATH=/frodo modules_install
=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel/
@@ -410,20 +433,22 @@
calling "make." This has effect when installing both in-tree
and out-of-tree modules.
---- 5.2 INSTALL_MOD_DIR
+5.2 INSTALL_MOD_DIR
+-------------------
External modules are by default installed to a directory under
/lib/modules/$(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."
+ alternative name to "extra."::
$ make INSTALL_MOD_DIR=gandalf -C $KDIR \
M=$PWD modules_install
=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf/
-=== 6. Module Versioning
+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
@@ -435,26 +460,33 @@
Module.symvers contains a list of all exported symbols from a kernel
build.
---- 6.1 Symbols From the Kernel (vmlinux + modules)
+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>
+ The syntax of the Module.symvers file is::
- 0x2d036834 scsi_remove_host drivers/scsi/scsi_mod
+ <CRC> <Symbol> <Namespace> <Module> <Export Type>
+
+ 0xe1cc2a05 usb_stor_suspend USB_STORAGE drivers/usb/storage/usb-storage EXPORT_SYMBOL_GPL
+
+ The fields are separated by tabs and values may be empty (e.g.
+ if no namespace is defined for an exported symbol).
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
+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
@@ -466,10 +498,11 @@
will be written containing all exported symbols that were not
defined in the kernel.
---- 6.3 Symbols From Another External Module
+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
+ 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.
@@ -481,17 +514,17 @@
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:
+ directory layout::
- ./foo/ <= contains foo.ko
- ./bar/ <= contains bar.ko
+ ./foo/ <= contains foo.ko
+ ./bar/ <= contains bar.ko
- The top-level kbuild file would then look like:
+ The top-level kbuild file would then look like::
- #./Kbuild (or ./Makefile):
- obj-y := foo/ bar/
+ #./Kbuild (or ./Makefile):
+ obj-m := foo/ bar/
- And executing
+ And executing::
$ make -C $KDIR M=$PWD
@@ -518,14 +551,16 @@
initialization of its symbol tables.
-=== 7. Tips & Tricks
+7. Tips & Tricks
+================
---- 7.1 Testing for CONFIG_FOO_BAR
+7.1 Testing for CONFIG_FOO_BAR
+------------------------------
- Modules often need to check for certain CONFIG_ options to
+ 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.
+ kbuild this is done by referencing the `CONFIG_` variable
+ directly::
#fs/ext2/Makefile
obj-$(CONFIG_EXT2_FS) += ext2.o
@@ -534,8 +569,7 @@
ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
External modules have traditionally used "grep" to check for
- specific CONFIG_ settings directly in .config. This usage is
+ 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.
-
+ in-tree modules when testing for `CONFIG_` definitions.
diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst
new file mode 100644
index 0000000..5033938
--- /dev/null
+++ b/Documentation/kbuild/reproducible-builds.rst
@@ -0,0 +1,127 @@
+===================
+Reproducible builds
+===================
+
+It is generally desirable that building the same source code with
+the same set of tools is reproducible, i.e. the output is always
+exactly the same. This makes it possible to verify that the build
+infrastructure for a binary distribution or embedded system has not
+been subverted. This can also make it easier to verify that a source
+or tool change does not make any difference to the resulting binaries.
+
+The `Reproducible Builds project`_ has more information about this
+general topic. This document covers the various reasons why building
+the kernel may be unreproducible, and how to avoid them.
+
+Timestamps
+----------
+
+The kernel embeds timestamps in three places:
+
+* The version string exposed by ``uname()`` and included in
+ ``/proc/version``
+
+* File timestamps in the embedded initramfs
+
+* If enabled via ``CONFIG_IKHEADERS``, file timestamps of kernel
+ headers embedded in the kernel or respective module,
+ exposed via ``/sys/kernel/kheaders.tar.xz``
+
+By default the timestamp is the current time and in the case of
+``kheaders`` the various files' modification times. This must
+be overridden using the `KBUILD_BUILD_TIMESTAMP`_ variable.
+If you are building from a git commit, you could use its commit date.
+
+The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,
+and enables warnings if they are used. If you incorporate external
+code that does use these, you must override the timestamp they
+correspond to by setting the `SOURCE_DATE_EPOCH`_ environment
+variable.
+
+User, host
+----------
+
+The kernel embeds the building user and host names in
+``/proc/version``. These must be overridden using the
+`KBUILD_BUILD_USER and KBUILD_BUILD_HOST`_ variables. If you are
+building from a git commit, you could use its committer address.
+
+Absolute filenames
+------------------
+
+When the kernel is built out-of-tree, debug information may include
+absolute filenames for the source files. This must be overridden by
+including the ``-fdebug-prefix-map`` option in the `KCFLAGS`_ variable.
+
+Depending on the compiler used, the ``__FILE__`` macro may also expand
+to an absolute filename in an out-of-tree build. Kbuild automatically
+uses the ``-fmacro-prefix-map`` option to prevent this, if it is
+supported.
+
+The Reproducible Builds web site has more information about these
+`prefix-map options`_.
+
+Generated files in source packages
+----------------------------------
+
+The build processes for some programs under the ``tools/``
+subdirectory do not completely support out-of-tree builds. This may
+cause a later source package build using e.g. ``make rpm-pkg`` to
+include generated files. You should ensure the source tree is
+pristine by running ``make mrproper`` or ``git clean -d -f -x`` before
+building a source package.
+
+Module signing
+--------------
+
+If you enable ``CONFIG_MODULE_SIG_ALL``, the default behaviour is to
+generate a different temporary key for each build, resulting in the
+modules being unreproducible. However, including a signing key with
+your source would presumably defeat the purpose of signing modules.
+
+One approach to this is to divide up the build process so that the
+unreproducible parts can be treated as sources:
+
+1. Generate a persistent signing key. Add the certificate for the key
+ to the kernel source.
+
+2. Set the ``CONFIG_SYSTEM_TRUSTED_KEYS`` symbol to include the
+ signing key's certificate, set ``CONFIG_MODULE_SIG_KEY`` to an
+ empty string, and disable ``CONFIG_MODULE_SIG_ALL``.
+ Build the kernel and modules.
+
+3. Create detached signatures for the modules, and publish them as
+ sources.
+
+4. Perform a second build that attaches the module signatures. It
+ can either rebuild the modules or use the output of step 2.
+
+Structure randomisation
+-----------------------
+
+If you enable ``CONFIG_GCC_PLUGIN_RANDSTRUCT``, you will need to
+pre-generate the random seed in
+``scripts/gcc-plgins/randomize_layout_seed.h`` so the same value
+is used in rebuilds.
+
+Debug info conflicts
+--------------------
+
+This is not a problem of unreproducibility, but of generated files
+being *too* reproducible.
+
+Once you set all the necessary variables for a reproducible build, a
+vDSO's debug information may be identical even for different kernel
+versions. This can result in file conflicts between debug information
+packages for the different kernel versions.
+
+To avoid this, you can make the vDSO different for different
+kernel versions by including an arbitrary string of "salt" in it.
+This is specified by the Kconfig symbol ``CONFIG_BUILD_SALT``.
+
+.. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp
+.. _KBUILD_BUILD_USER and KBUILD_BUILD_HOST: kbuild.html#kbuild-build-user-kbuild-build-host
+.. _KCFLAGS: kbuild.html#kcflags
+.. _prefix-map options: https://reproducible-builds.org/docs/build-path/
+.. _Reproducible Builds project: https://reproducible-builds.org/
+.. _SOURCE_DATE_EPOCH: https://reproducible-builds.org/docs/source-date-epoch/