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 94PROCMACROLDFLAGS 95---------------- 96Flags to be passed when linking Rust proc macros. Since proc macros are loaded 97by rustc at build time, they must be linked in a way that is compatible with 98the rustc toolchain being used. 99 100For instance, it can be useful when rustc uses a different C library than 101the one the user wants to use for host programs. 102 103If unset, it defaults to the flags passed when linking host programs. 104 105HOSTLDFLAGS 106----------- 107Additional flags to be passed when linking host programs. 108 109HOSTLDLIBS 110---------- 111Additional libraries to link against when building host programs. 112 113.. _userkbuildflags: 114 115USERCFLAGS 116---------- 117Additional options used for $(CC) when compiling userprogs. 118 119USERLDFLAGS 120----------- 121Additional options used for $(LD) when linking userprogs. userprogs are linked 122with CC, so $(USERLDFLAGS) should include "-Wl," prefix as applicable. 123 124KBUILD_KCONFIG 125-------------- 126Set the top-level Kconfig file to the value of this environment 127variable. The default name is "Kconfig". 128 129KBUILD_VERBOSE 130-------------- 131Set the kbuild verbosity. Can be assigned same values as "V=...". 132 133See make help for the full list. 134 135Setting "V=..." takes precedence over KBUILD_VERBOSE. 136 137KBUILD_EXTMOD 138------------- 139Set the directory to look for the kernel source when building external 140modules. 141 142Setting "M=..." takes precedence over KBUILD_EXTMOD. 143 144KBUILD_OUTPUT 145------------- 146Specify the output directory when building the kernel. 147 148This variable can also be used to point to the kernel output directory when 149building external modules against a pre-built kernel in a separate build 150directory. Please note that this does NOT specify the output directory for the 151external modules themselves. (Use KBUILD_EXTMOD_OUTPUT for that purpose.) 152 153The output directory can also be specified using "O=...". 154 155Setting "O=..." takes precedence over KBUILD_OUTPUT. 156 157KBUILD_EXTMOD_OUTPUT 158-------------------- 159Specify the output directory for external modules. 160 161Setting "MO=..." takes precedence over KBUILD_EXTMOD_OUTPUT. 162 163KBUILD_EXTRA_WARN 164----------------- 165Specify the extra build checks. The same value can be assigned by passing 166W=... from the command line. 167 168See `make help` for the list of the supported values. 169 170Setting "W=..." takes precedence over KBUILD_EXTRA_WARN. 171 172KBUILD_DEBARCH 173-------------- 174For the deb-pkg target, allows overriding the normal heuristics deployed by 175deb-pkg. Normally deb-pkg attempts to guess the right architecture based on 176the UTS_MACHINE variable, and on some architectures also the kernel config. 177The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian 178architecture. 179 180KDOCFLAGS 181--------- 182Specify extra (warning/error) flags for kernel-doc checks during the build, 183see scripts/kernel-doc for which flags are supported. Note that this doesn't 184(currently) apply to documentation builds. 185 186ARCH 187---- 188Set ARCH to the architecture to be built. 189 190In most cases the name of the architecture is the same as the 191directory name found in the arch/ directory. 192 193But some architectures such as x86 and sparc have aliases. 194 195- x86: i386 for 32 bit, x86_64 for 64 bit 196- parisc: parisc64 for 64 bit 197- sparc: sparc32 for 32 bit, sparc64 for 64 bit 198 199CROSS_COMPILE 200------------- 201Specify an optional fixed part of the binutils filename. 202CROSS_COMPILE can be a part of the filename or the full path. 203 204CROSS_COMPILE is also used for ccache in some setups. 205 206CF 207-- 208Additional options for sparse. 209 210CF is often used on the command-line like this:: 211 212 make CF=-Wbitwise C=2 213 214INSTALL_PATH 215------------ 216INSTALL_PATH specifies where to place the updated kernel and system map 217images. Default is /boot, but you can set it to other values. 218 219INSTALLKERNEL 220------------- 221Install script called when using "make install". 222The default name is "installkernel". 223 224The script will be called with the following arguments: 225 226 - $1 - kernel version 227 - $2 - kernel image file 228 - $3 - kernel map file 229 - $4 - default install path (use root directory if blank) 230 231The implementation of "make install" is architecture specific 232and it may differ from the above. 233 234INSTALLKERNEL is provided to enable the possibility to 235specify a custom installer when cross compiling a kernel. 236 237MODLIB 238------ 239Specify where to install modules. 240The default value is:: 241 242 $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE) 243 244The value can be overridden in which case the default value is ignored. 245 246INSTALL_MOD_PATH 247---------------- 248INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory 249relocations required by build roots. This is not defined in the 250makefile but the argument can be passed to make if needed. 251 252INSTALL_MOD_STRIP 253----------------- 254INSTALL_MOD_STRIP, if defined, will cause modules to be 255stripped after they are installed. If INSTALL_MOD_STRIP is '1', then 256the default option --strip-debug will be used. Otherwise, 257INSTALL_MOD_STRIP value will be used as the options to the strip command. 258 259INSTALL_HDR_PATH 260---------------- 261INSTALL_HDR_PATH specifies where to install user space headers when 262executing "make headers_*". 263 264The default value is:: 265 266 $(objtree)/usr 267 268$(objtree) is the directory where output files are saved. 269The output directory is often set using "O=..." on the commandline. 270 271The value can be overridden in which case the default value is ignored. 272 273INSTALL_DTBS_PATH 274----------------- 275INSTALL_DTBS_PATH specifies where to install device tree blobs for 276relocations required by build roots. This is not defined in the 277makefile but the argument can be passed to make if needed. 278 279KBUILD_ABS_SRCTREE 280-------------------------------------------------- 281Kbuild uses a relative path to point to the tree when possible. For instance, 282when building in the source tree, the source tree path is '.' 283 284Setting this flag requests Kbuild to use absolute path to the source tree. 285There are some useful cases to do so, like when generating tag files with 286absolute path entries etc. 287 288KBUILD_SIGN_PIN 289--------------- 290This variable allows a passphrase or PIN to be passed to the sign-file 291utility when signing kernel modules, if the private key requires such. 292 293KBUILD_MODPOST_WARN 294------------------- 295KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined 296symbols in the final module linking stage. It changes such errors 297into warnings. 298 299KBUILD_MODPOST_NOFINAL 300---------------------- 301KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules. 302This is solely useful to speed up test compiles. 303 304KBUILD_EXTRA_SYMBOLS 305-------------------- 306For modules that use symbols from other modules. 307See more details in modules.rst. 308 309ALLSOURCE_ARCHS 310--------------- 311For tags/TAGS/cscope targets, you can specify more than one arch 312to be included in the databases, separated by blank space. E.g.:: 313 314 $ make ALLSOURCE_ARCHS="x86 mips arm" tags 315 316To get all available archs you can also specify all. E.g.:: 317 318 $ make ALLSOURCE_ARCHS=all tags 319 320IGNORE_DIRS 321----------- 322For tags/TAGS/cscope targets, you can choose which directories won't 323be included in the databases, separated by blank space. E.g.:: 324 325 $ make IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope 326 327KBUILD_BUILD_TIMESTAMP 328---------------------- 329Setting this to a date string overrides the timestamp used in the 330UTS_VERSION definition (uname -v in the running kernel). The value has to 331be a string that can be passed to date -d. The default value 332is the output of the date command at one point during build. 333 334KBUILD_BUILD_USER, KBUILD_BUILD_HOST 335------------------------------------ 336These two variables allow to override the user@host string displayed during 337boot and in /proc/version. The default value is the output of the commands 338whoami and host, respectively. 339 340LLVM 341---- 342If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead 343of GCC and GNU binutils to build the kernel. 344