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
 25modules.builtin.ranges
 26----------------------
 27This file contains address offset ranges (per ELF section) for all modules
 28that are built into the kernel. Together with System.map, it can be used
 29to associate module names with symbols.
 30
 31Environment variables
 32=====================
 33
 34KCPPFLAGS
 35---------
 36Additional options to pass when preprocessing. The preprocessing options
 37will be used in all cases where kbuild does preprocessing including
 38building C files and assembler files.
 39
 40KAFLAGS
 41-------
 42Additional options to the assembler (for built-in and modules).
 43
 44AFLAGS_MODULE
 45-------------
 46Additional assembler options for modules.
 47
 48AFLAGS_KERNEL
 49-------------
 50Additional assembler options for built-in.
 51
 52KCFLAGS
 53-------
 54Additional options to the C compiler (for built-in and modules).
 55
 56KRUSTFLAGS
 57----------
 58Additional options to the Rust compiler (for built-in and modules).
 59
 60CFLAGS_KERNEL
 61-------------
 62Additional options for $(CC) when used to compile
 63code that is compiled as built-in.
 64
 65CFLAGS_MODULE
 66-------------
 67Additional module specific options to use for $(CC).
 68
 69RUSTFLAGS_KERNEL
 70----------------
 71Additional options for $(RUSTC) when used to compile
 72code that is compiled as built-in.
 73
 74RUSTFLAGS_MODULE
 75----------------
 76Additional module specific options to use for $(RUSTC).
 77
 78LDFLAGS_MODULE
 79--------------
 80Additional options used for $(LD) when linking modules.
 81
 82HOSTCFLAGS
 83----------
 84Additional flags to be passed to $(HOSTCC) when building host programs.
 85
 86HOSTCXXFLAGS
 87------------
 88Additional flags to be passed to $(HOSTCXX) when building host programs.
 89
 90HOSTRUSTFLAGS
 91-------------
 92Additional flags to be passed to $(HOSTRUSTC) when building host programs.
 93
 94HOSTLDFLAGS
 95-----------
 96Additional flags to be passed when linking host programs.
 97
 98HOSTLDLIBS
 99----------
100Additional libraries to link against when building host programs.
101
102.. _userkbuildflags:
103
104USERCFLAGS
105----------
106Additional options used for $(CC) when compiling userprogs.
107
108USERLDFLAGS
109-----------
110Additional options used for $(LD) when linking userprogs. userprogs are linked
111with CC, so $(USERLDFLAGS) should include "-Wl," prefix as applicable.
112
113KBUILD_KCONFIG
114--------------
115Set the top-level Kconfig file to the value of this environment
116variable.  The default name is "Kconfig".
117
118KBUILD_VERBOSE
119--------------
120Set the kbuild verbosity. Can be assigned same values as "V=...".
121
122See make help for the full list.
123
124Setting "V=..." takes precedence over KBUILD_VERBOSE.
125
126KBUILD_EXTMOD
127-------------
128Set the directory to look for the kernel source when building external
129modules.
130
131Setting "M=..." takes precedence over KBUILD_EXTMOD.
132
133KBUILD_OUTPUT
134-------------
135Specify the output directory when building the kernel.
136
137This variable can also be used to point to the kernel output directory when
138building external modules against a pre-built kernel in a separate build
139directory. Please note that this does NOT specify the output directory for the
140external modules themselves. (Use KBUILD_EXTMOD_OUTPUT for that purpose.)
141
142The output directory can also be specified using "O=...".
143
144Setting "O=..." takes precedence over KBUILD_OUTPUT.
145
146KBUILD_EXTMOD_OUTPUT
147--------------------
148Specify the output directory for external modules.
149
150Setting "MO=..." takes precedence over KBUILD_EXTMOD_OUTPUT.
151
152KBUILD_EXTRA_WARN
153-----------------
154Specify the extra build checks. The same value can be assigned by passing
155W=... from the command line.
156
157See `make help` for the list of the supported values.
158
159Setting "W=..." takes precedence over KBUILD_EXTRA_WARN.
160
161KBUILD_DEBARCH
162--------------
163For the deb-pkg target, allows overriding the normal heuristics deployed by
164deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
165the UTS_MACHINE variable, and on some architectures also the kernel config.
166The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
167architecture.
168
169KDOCFLAGS
170---------
171Specify extra (warning/error) flags for kernel-doc checks during the build,
172see scripts/kernel-doc for which flags are supported. Note that this doesn't
173(currently) apply to documentation builds.
174
175ARCH
176----
177Set ARCH to the architecture to be built.
178
179In most cases the name of the architecture is the same as the
180directory name found in the arch/ directory.
181
182But some architectures such as x86 and sparc have aliases.
183
184- x86: i386 for 32 bit, x86_64 for 64 bit
185- parisc: parisc64 for 64 bit
186- sparc: sparc32 for 32 bit, sparc64 for 64 bit
187
188CROSS_COMPILE
189-------------
190Specify an optional fixed part of the binutils filename.
191CROSS_COMPILE can be a part of the filename or the full path.
192
193CROSS_COMPILE is also used for ccache in some setups.
194
195CF
196--
197Additional options for sparse.
198
199CF is often used on the command-line like this::
200
201    make CF=-Wbitwise C=2
202
203INSTALL_PATH
204------------
205INSTALL_PATH specifies where to place the updated kernel and system map
206images. Default is /boot, but you can set it to other values.
207
208INSTALLKERNEL
209-------------
210Install script called when using "make install".
211The default name is "installkernel".
212
213The script will be called with the following arguments:
214
215   - $1 - kernel version
216   - $2 - kernel image file
217   - $3 - kernel map file
218   - $4 - default install path (use root directory if blank)
219
220The implementation of "make install" is architecture specific
221and it may differ from the above.
222
223INSTALLKERNEL is provided to enable the possibility to
224specify a custom installer when cross compiling a kernel.
225
226MODLIB
227------
228Specify where to install modules.
229The default value is::
230
231     $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
232
233The value can be overridden in which case the default value is ignored.
234
235INSTALL_MOD_PATH
236----------------
237INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
238relocations required by build roots.  This is not defined in the
239makefile but the argument can be passed to make if needed.
240
241INSTALL_MOD_STRIP
242-----------------
243INSTALL_MOD_STRIP, if defined, will cause modules to be
244stripped after they are installed.  If INSTALL_MOD_STRIP is '1', then
245the default option --strip-debug will be used.  Otherwise,
246INSTALL_MOD_STRIP value will be used as the options to the strip command.
247
248INSTALL_HDR_PATH
249----------------
250INSTALL_HDR_PATH specifies where to install user space headers when
251executing "make headers_*".
252
253The default value is::
254
255    $(objtree)/usr
256
257$(objtree) is the directory where output files are saved.
258The output directory is often set using "O=..." on the commandline.
259
260The value can be overridden in which case the default value is ignored.
261
262INSTALL_DTBS_PATH
263-----------------
264INSTALL_DTBS_PATH specifies where to install device tree blobs for
265relocations required by build roots.  This is not defined in the
266makefile but the argument can be passed to make if needed.
267
268KBUILD_ABS_SRCTREE
269--------------------------------------------------
270Kbuild uses a relative path to point to the tree when possible. For instance,
271when building in the source tree, the source tree path is '.'
272
273Setting this flag requests Kbuild to use absolute path to the source tree.
274There are some useful cases to do so, like when generating tag files with
275absolute path entries etc.
276
277KBUILD_SIGN_PIN
278---------------
279This variable allows a passphrase or PIN to be passed to the sign-file
280utility when signing kernel modules, if the private key requires such.
281
282KBUILD_MODPOST_WARN
283-------------------
284KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
285symbols in the final module linking stage. It changes such errors
286into warnings.
287
288KBUILD_MODPOST_NOFINAL
289----------------------
290KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
291This is solely useful to speed up test compiles.
292
293KBUILD_EXTRA_SYMBOLS
294--------------------
295For modules that use symbols from other modules.
296See more details in modules.rst.
297
298ALLSOURCE_ARCHS
299---------------
300For tags/TAGS/cscope targets, you can specify more than one arch
301to be included in the databases, separated by blank space. E.g.::
302
303    $ make ALLSOURCE_ARCHS="x86 mips arm" tags
304
305To get all available archs you can also specify all. E.g.::
306
307    $ make ALLSOURCE_ARCHS=all tags
308
309IGNORE_DIRS
310-----------
311For tags/TAGS/cscope targets, you can choose which directories won't
312be included in the databases, separated by blank space. E.g.::
313
314    $ make IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope
315
316KBUILD_BUILD_TIMESTAMP
317----------------------
318Setting this to a date string overrides the timestamp used in the
319UTS_VERSION definition (uname -v in the running kernel). The value has to
320be a string that can be passed to date -d. The default value
321is the output of the date command at one point during build.
322
323KBUILD_BUILD_USER, KBUILD_BUILD_HOST
324------------------------------------
325These two variables allow to override the user@host string displayed during
326boot and in /proc/version. The default value is the output of the commands
327whoami and host, respectively.
328
329LLVM
330----
331If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
332of GCC and GNU binutils to build the kernel.

  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
 
 
 
 
 
 
153ARCH
154----
155Set ARCH to the architecture to be built.
156
157In most cases the name of the architecture is the same as the
158directory name found in the arch/ directory.
159
160But some architectures such as x86 and sparc have aliases.
161
162- x86: i386 for 32 bit, x86_64 for 64 bit
163- sh: sh for 32 bit, sh64 for 64 bit
164- sparc: sparc32 for 32 bit, sparc64 for 64 bit
165
166CROSS_COMPILE
167-------------
168Specify an optional fixed part of the binutils filename.
169CROSS_COMPILE can be a part of the filename or the full path.
170
171CROSS_COMPILE is also used for ccache in some setups.
172
173CF
174--
175Additional options for sparse.
176
177CF is often used on the command-line like this::
178
179    make CF=-Wbitwise C=2
180
181INSTALL_PATH
182------------
183INSTALL_PATH specifies where to place the updated kernel and system map
184images. Default is /boot, but you can set it to other values.
185
186INSTALLKERNEL
187-------------
188Install script called when using "make install".
189The default name is "installkernel".
190
191The script will be called with the following arguments:
192
193   - $1 - kernel version
194   - $2 - kernel image file
195   - $3 - kernel map file
196   - $4 - default install path (use root directory if blank)
197
198The implementation of "make install" is architecture specific
199and it may differ from the above.
200
201INSTALLKERNEL is provided to enable the possibility to
202specify a custom installer when cross compiling a kernel.
203
204MODLIB
205------
206Specify where to install modules.
207The default value is::
208
209     $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
210
211The value can be overridden in which case the default value is ignored.
212
213INSTALL_MOD_PATH
214----------------
215INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
216relocations required by build roots.  This is not defined in the
217makefile but the argument can be passed to make if needed.
218
219INSTALL_MOD_STRIP
220-----------------
221INSTALL_MOD_STRIP, if defined, will cause modules to be
222stripped after they are installed.  If INSTALL_MOD_STRIP is '1', then
223the default option --strip-debug will be used.  Otherwise,
224INSTALL_MOD_STRIP value will be used as the options to the strip command.
225
226INSTALL_HDR_PATH
227----------------
228INSTALL_HDR_PATH specifies where to install user space headers when
229executing "make headers_*".
230
231The default value is::
232
233    $(objtree)/usr
234
235$(objtree) is the directory where output files are saved.
236The output directory is often set using "O=..." on the commandline.
237
238The value can be overridden in which case the default value is ignored.
239
 
 
 
 
 
 
240KBUILD_ABS_SRCTREE
241--------------------------------------------------
242Kbuild uses a relative path to point to the tree when possible. For instance,
243when building in the source tree, the source tree path is '.'
244
245Setting this flag requests Kbuild to use absolute path to the source tree.
246There are some useful cases to do so, like when generating tag files with
247absolute path entries etc.
248
249KBUILD_SIGN_PIN
250---------------
251This variable allows a passphrase or PIN to be passed to the sign-file
252utility when signing kernel modules, if the private key requires such.
253
254KBUILD_MODPOST_WARN
255-------------------
256KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
257symbols in the final module linking stage. It changes such errors
258into warnings.
259
260KBUILD_MODPOST_NOFINAL
261----------------------
262KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
263This is solely useful to speed up test compiles.
264
265KBUILD_EXTRA_SYMBOLS
266--------------------
267For modules that use symbols from other modules.
268See more details in modules.rst.
269
270ALLSOURCE_ARCHS
271---------------
272For tags/TAGS/cscope targets, you can specify more than one arch
273to be included in the databases, separated by blank space. E.g.::
274
275    $ make ALLSOURCE_ARCHS="x86 mips arm" tags
276
277To get all available archs you can also specify all. E.g.::
278
279    $ make ALLSOURCE_ARCHS=all tags
 
 
 
 
 
 
 
280
281KBUILD_BUILD_TIMESTAMP
282----------------------
283Setting this to a date string overrides the timestamp used in the
284UTS_VERSION definition (uname -v in the running kernel). The value has to
285be a string that can be passed to date -d. The default value
286is the output of the date command at one point during build.
287
288KBUILD_BUILD_USER, KBUILD_BUILD_HOST
289------------------------------------
290These two variables allow to override the user@host string displayed during
291boot and in /proc/version. The default value is the output of the commands
292whoami and host, respectively.
293
294LLVM
295----
296If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
297of GCC and GNU binutils to build the kernel.