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- parisc: parisc64 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 281IGNORE_DIRS 282----------- 283For tags/TAGS/cscope targets, you can choose which directories won't 284be included in the databases, separated by blank space. E.g.:: 285 286 $ make IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope 287 288KBUILD_BUILD_TIMESTAMP 289---------------------- 290Setting this to a date string overrides the timestamp used in the 291UTS_VERSION definition (uname -v in the running kernel). The value has to 292be a string that can be passed to date -d. The default value 293is the output of the date command at one point during build. 294 295KBUILD_BUILD_USER, KBUILD_BUILD_HOST 296------------------------------------ 297These two variables allow to override the user@host string displayed during 298boot and in /proc/version. The default value is the output of the commands 299whoami and host, respectively. 300 301LLVM 302---- 303If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead 304of GCC and GNU binutils to build the kernel. 305