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
51KRUSTFLAGS
52----------
53Additional options to the Rust compiler (for built-in and modules).
54
55CFLAGS_KERNEL
56-------------
57Additional options for $(CC) when used to compile
58code that is compiled as built-in.
59
60CFLAGS_MODULE
61-------------
62Additional module specific options to use for $(CC).
63
64RUSTFLAGS_KERNEL
65----------------
66Additional options for $(RUSTC) when used to compile
67code that is compiled as built-in.
68
69RUSTFLAGS_MODULE
70----------------
71Additional module specific options to use for $(RUSTC).
72
73LDFLAGS_MODULE
74--------------
75Additional options used for $(LD) when linking modules.
76
77HOSTCFLAGS
78----------
79Additional flags to be passed to $(HOSTCC) when building host programs.
80
81HOSTCXXFLAGS
82------------
83Additional flags to be passed to $(HOSTCXX) when building host programs.
84
85HOSTRUSTFLAGS
86-------------
87Additional flags to be passed to $(HOSTRUSTC) when building host programs.
88
89HOSTLDFLAGS
90-----------
91Additional flags to be passed when linking host programs.
92
93HOSTLDLIBS
94----------
95Additional libraries to link against when building host programs.
96
97.. _userkbuildflags:
98
99USERCFLAGS
100----------
101Additional options used for $(CC) when compiling userprogs.
102
103USERLDFLAGS
104-----------
105Additional options used for $(LD) when linking userprogs. userprogs are linked
106with CC, so $(USERLDFLAGS) should include "-Wl," prefix as applicable.
107
108KBUILD_KCONFIG
109--------------
110Set the top-level Kconfig file to the value of this environment
111variable.  The default name is "Kconfig".
112
113KBUILD_VERBOSE
114--------------
115Set the kbuild verbosity. Can be assigned same values as "V=...".
116
117See make help for the full list.
118
119Setting "V=..." takes precedence over KBUILD_VERBOSE.
120
121KBUILD_EXTMOD
122-------------
123Set the directory to look for the kernel source when building external
124modules.
125
126Setting "M=..." takes precedence over KBUILD_EXTMOD.
127
128KBUILD_OUTPUT
129-------------
130Specify the output directory when building the kernel.
131
132The output directory can also be specified using "O=...".
133
134Setting "O=..." takes precedence over KBUILD_OUTPUT.
135
136KBUILD_EXTRA_WARN
137-----------------
138Specify the extra build checks. The same value can be assigned by passing
139W=... from the command line.
140
141See `make help` for the list of the supported values.
142
143Setting "W=..." takes precedence over KBUILD_EXTRA_WARN.
144
145KBUILD_DEBARCH
146--------------
147For the deb-pkg target, allows overriding the normal heuristics deployed by
148deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
149the UTS_MACHINE variable, and on some architectures also the kernel config.
150The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
151architecture.
152
153KDOCFLAGS
154---------
155Specify extra (warning/error) flags for kernel-doc checks during the build,
156see scripts/kernel-doc for which flags are supported. Note that this doesn't
157(currently) apply to documentation builds.
158
159ARCH
160----
161Set ARCH to the architecture to be built.
162
163In most cases the name of the architecture is the same as the
164directory name found in the arch/ directory.
165
166But some architectures such as x86 and sparc have aliases.
167
168- x86: i386 for 32 bit, x86_64 for 64 bit
169- parisc: parisc64 for 64 bit
170- sparc: sparc32 for 32 bit, sparc64 for 64 bit
171
172CROSS_COMPILE
173-------------
174Specify an optional fixed part of the binutils filename.
175CROSS_COMPILE can be a part of the filename or the full path.
176
177CROSS_COMPILE is also used for ccache in some setups.
178
179CF
180--
181Additional options for sparse.
182
183CF is often used on the command-line like this::
184
185    make CF=-Wbitwise C=2
186
187INSTALL_PATH
188------------
189INSTALL_PATH specifies where to place the updated kernel and system map
190images. Default is /boot, but you can set it to other values.
191
192INSTALLKERNEL
193-------------
194Install script called when using "make install".
195The default name is "installkernel".
196
197The script will be called with the following arguments:
198
199   - $1 - kernel version
200   - $2 - kernel image file
201   - $3 - kernel map file
202   - $4 - default install path (use root directory if blank)
203
204The implementation of "make install" is architecture specific
205and it may differ from the above.
206
207INSTALLKERNEL is provided to enable the possibility to
208specify a custom installer when cross compiling a kernel.
209
210MODLIB
211------
212Specify where to install modules.
213The default value is::
214
215     $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
216
217The value can be overridden in which case the default value is ignored.
218
219INSTALL_MOD_PATH
220----------------
221INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
222relocations required by build roots.  This is not defined in the
223makefile but the argument can be passed to make if needed.
224
225INSTALL_MOD_STRIP
226-----------------
227INSTALL_MOD_STRIP, if defined, will cause modules to be
228stripped after they are installed.  If INSTALL_MOD_STRIP is '1', then
229the default option --strip-debug will be used.  Otherwise,
230INSTALL_MOD_STRIP value will be used as the options to the strip command.
231
232INSTALL_HDR_PATH
233----------------
234INSTALL_HDR_PATH specifies where to install user space headers when
235executing "make headers_*".
236
237The default value is::
238
239    $(objtree)/usr
240
241$(objtree) is the directory where output files are saved.
242The output directory is often set using "O=..." on the commandline.
243
244The value can be overridden in which case the default value is ignored.
245
246INSTALL_DTBS_PATH
247-----------------
248INSTALL_DTBS_PATH specifies where to install device tree blobs for
249relocations required by build roots.  This is not defined in the
250makefile but the argument can be passed to make if needed.
251
252KBUILD_ABS_SRCTREE
253--------------------------------------------------
254Kbuild uses a relative path to point to the tree when possible. For instance,
255when building in the source tree, the source tree path is '.'
256
257Setting this flag requests Kbuild to use absolute path to the source tree.
258There are some useful cases to do so, like when generating tag files with
259absolute path entries etc.
260
261KBUILD_SIGN_PIN
262---------------
263This variable allows a passphrase or PIN to be passed to the sign-file
264utility when signing kernel modules, if the private key requires such.
265
266KBUILD_MODPOST_WARN
267-------------------
268KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
269symbols in the final module linking stage. It changes such errors
270into warnings.
271
272KBUILD_MODPOST_NOFINAL
273----------------------
274KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
275This is solely useful to speed up test compiles.
276
277KBUILD_EXTRA_SYMBOLS
278--------------------
279For modules that use symbols from other modules.
280See more details in modules.rst.
281
282ALLSOURCE_ARCHS
283---------------
284For tags/TAGS/cscope targets, you can specify more than one arch
285to be included in the databases, separated by blank space. E.g.::
286
287    $ make ALLSOURCE_ARCHS="x86 mips arm" tags
288
289To get all available archs you can also specify all. E.g.::
290
291    $ make ALLSOURCE_ARCHS=all tags
292
293IGNORE_DIRS
294-----------
295For tags/TAGS/cscope targets, you can choose which directories won't
296be included in the databases, separated by blank space. E.g.::
297
298    $ make IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope
299
300KBUILD_BUILD_TIMESTAMP
301----------------------
302Setting this to a date string overrides the timestamp used in the
303UTS_VERSION definition (uname -v in the running kernel). The value has to
304be a string that can be passed to date -d. The default value
305is the output of the date command at one point during build.
306
307KBUILD_BUILD_USER, KBUILD_BUILD_HOST
308------------------------------------
309These two variables allow to override the user@host string displayed during
310boot and in /proc/version. The default value is the output of the commands
311whoami and host, respectively.
312
313LLVM
314----
315If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
316of GCC and GNU binutils to build the kernel.
317