1======
2Kbuild
3======
4
5
6Output files
7============
8
9modules.order
10-------------
11This file records the order in which modules appear in Makefiles. This
12is used by modprobe to deterministically resolve aliases that match
13multiple modules.
14
15modules.builtin
16---------------
17This file lists all modules that are built into the kernel. This is used
18by modprobe to not fail when trying to load something builtin.
19
20modules.builtin.modinfo
21-----------------------
22This file contains modinfo from all modules that are built into the kernel.
23Unlike modinfo of a separate module, all fields are prefixed with module name.
24
25
26Environment variables
27=====================
28
29KCPPFLAGS
30---------
31Additional options to pass when preprocessing. The preprocessing options
32will be used in all cases where kbuild does preprocessing including
33building C files and assembler files.
34
35KAFLAGS
36-------
37Additional options to the assembler (for built-in and modules).
38
39AFLAGS_MODULE
40-------------
41Additional assembler options for modules.
42
43AFLAGS_KERNEL
44-------------
45Additional assembler options for built-in.
46
47KCFLAGS
48-------
49Additional options to the C compiler (for built-in and modules).
50
51CFLAGS_KERNEL
52-------------
53Additional options for $(CC) when used to compile
54code that is compiled as built-in.
55
56CFLAGS_MODULE
57-------------
58Additional module specific options to use for $(CC).
59
60LDFLAGS_MODULE
61--------------
62Additional options used for $(LD) when linking modules.
63
64HOSTCFLAGS
65----------
66Additional flags to be passed to $(HOSTCC) when building host programs.
67
68HOSTCXXFLAGS
69------------
70Additional flags to be passed to $(HOSTCXX) when building host programs.
71
72HOSTLDFLAGS
73-----------
74Additional flags to be passed when linking host programs.
75
76HOSTLDLIBS
77----------
78Additional libraries to link against when building host programs.
79
80KBUILD_KCONFIG
81--------------
82Set the top-level Kconfig file to the value of this environment
83variable.  The default name is "Kconfig".
84
85KBUILD_VERBOSE
86--------------
87Set the kbuild verbosity. Can be assigned same values as "V=...".
88
89See make help for the full list.
90
91Setting "V=..." takes precedence over KBUILD_VERBOSE.
92
93KBUILD_EXTMOD
94-------------
95Set the directory to look for the kernel source when building external
96modules.
97
98Setting "M=..." takes precedence over KBUILD_EXTMOD.
99
100KBUILD_OUTPUT
101-------------
102Specify the output directory when building the kernel.
103
104The output directory can also be specified using "O=...".
105
106Setting "O=..." takes precedence over KBUILD_OUTPUT.
107
108KBUILD_EXTRA_WARN
109-----------------
110Specify the extra build checks. The same value can be assigned by passing
111W=... from the command line.
112
113See `make help` for the list of the supported values.
114
115Setting "W=..." takes precedence over KBUILD_EXTRA_WARN.
116
117KBUILD_DEBARCH
118--------------
119For the deb-pkg target, allows overriding the normal heuristics deployed by
120deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
121the UTS_MACHINE variable, and on some architectures also the kernel config.
122The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
123architecture.
124
125ARCH
126----
127Set ARCH to the architecture to be built.
128
129In most cases the name of the architecture is the same as the
130directory name found in the arch/ directory.
131
132But some architectures such as x86 and sparc have aliases.
133
134- x86: i386 for 32 bit, x86_64 for 64 bit
135- sh: sh for 32 bit, sh64 for 64 bit
136- sparc: sparc32 for 32 bit, sparc64 for 64 bit
137
138CROSS_COMPILE
139-------------
140Specify an optional fixed part of the binutils filename.
141CROSS_COMPILE can be a part of the filename or the full path.
142
143CROSS_COMPILE is also used for ccache in some setups.
144
145CF
146--
147Additional options for sparse.
148
149CF is often used on the command-line like this::
150
151    make CF=-Wbitwise C=2
152
153INSTALL_PATH
154------------
155INSTALL_PATH specifies where to place the updated kernel and system map
156images. Default is /boot, but you can set it to other values.
157
158INSTALLKERNEL
159-------------
160Install script called when using "make install".
161The default name is "installkernel".
162
163The script will be called with the following arguments:
164
165   - $1 - kernel version
166   - $2 - kernel image file
167   - $3 - kernel map file
168   - $4 - default install path (use root directory if blank)
169
170The implementation of "make install" is architecture specific
171and it may differ from the above.
172
173INSTALLKERNEL is provided to enable the possibility to
174specify a custom installer when cross compiling a kernel.
175
176MODLIB
177------
178Specify where to install modules.
179The default value is::
180
181     $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
182
183The value can be overridden in which case the default value is ignored.
184
185INSTALL_MOD_PATH
186----------------
187INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
188relocations required by build roots.  This is not defined in the
189makefile but the argument can be passed to make if needed.
190
191INSTALL_MOD_STRIP
192-----------------
193INSTALL_MOD_STRIP, if defined, will cause modules to be
194stripped after they are installed.  If INSTALL_MOD_STRIP is '1', then
195the default option --strip-debug will be used.  Otherwise,
196INSTALL_MOD_STRIP value will be used as the options to the strip command.
197
198INSTALL_HDR_PATH
199----------------
200INSTALL_HDR_PATH specifies where to install user space headers when
201executing "make headers_*".
202
203The default value is::
204
205    $(objtree)/usr
206
207$(objtree) is the directory where output files are saved.
208The output directory is often set using "O=..." on the commandline.
209
210The value can be overridden in which case the default value is ignored.
211
212KBUILD_ABS_SRCTREE
213--------------------------------------------------
214Kbuild uses a relative path to point to the tree when possible. For instance,
215when building in the source tree, the source tree path is '.'
216
217Setting this flag requests Kbuild to use absolute path to the source tree.
218There are some useful cases to do so, like when generating tag files with
219absolute path entries etc.
220
221KBUILD_SIGN_PIN
222---------------
223This variable allows a passphrase or PIN to be passed to the sign-file
224utility when signing kernel modules, if the private key requires such.
225
226KBUILD_MODPOST_WARN
227-------------------
228KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
229symbols in the final module linking stage. It changes such errors
230into warnings.
231
232KBUILD_MODPOST_NOFINAL
233----------------------
234KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
235This is solely useful to speed up test compiles.
236
237KBUILD_EXTRA_SYMBOLS
238--------------------
239For modules that use symbols from other modules.
240See more details in modules.rst.
241
242ALLSOURCE_ARCHS
243---------------
244For tags/TAGS/cscope targets, you can specify more than one arch
245to be included in the databases, separated by blank space. E.g.::
246
247    $ make ALLSOURCE_ARCHS="x86 mips arm" tags
248
249To get all available archs you can also specify all. E.g.::
250
251    $ make ALLSOURCE_ARCHS=all tags
252
253KBUILD_BUILD_TIMESTAMP
254----------------------
255Setting this to a date string overrides the timestamp used in the
256UTS_VERSION definition (uname -v in the running kernel). The value has to
257be a string that can be passed to date -d. The default value
258is the output of the date command at one point during build.
259
260KBUILD_BUILD_USER, KBUILD_BUILD_HOST
261------------------------------------
262These two variables allow to override the user@host string displayed during
263boot and in /proc/version. The default value is the output of the commands
264whoami and host, respectively.
265
266LLVM
267----
268If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
269of GCC and GNU binutils to build the kernel.
270