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. 333