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 51CFLAGS_KERNEL 52------------- 53Additional options for $(CC) when used to compile 54code that is compiled as built-in. 55 56CFLAGS_MODULE 57------------- 58Additional module specific options to use for $(CC). 59 60LDFLAGS_MODULE 61-------------- 62Additional options used for $(LD) when linking modules. 63 64HOSTCFLAGS 65---------- 66Additional flags to be passed to $(HOSTCC) when building host programs. 67 68HOSTCXXFLAGS 69------------ 70Additional flags to be passed to $(HOSTCXX) when building host programs. 71 72HOSTLDFLAGS 73----------- 74Additional flags to be passed when linking host programs. 75 76HOSTLDLIBS 77---------- 78Additional libraries to link against when building host programs. 79 80.. _userkbuildflags: 81 82USERCFLAGS 83---------- 84Additional options used for $(CC) when compiling userprogs. 85 86USERLDFLAGS 87----------- 88Additional options used for $(LD) when linking userprogs. userprogs are linked 89with CC, so $(USERLDFLAGS) should include "-Wl," prefix as applicable. 90 91KBUILD_KCONFIG 92-------------- 93Set the top-level Kconfig file to the value of this environment 94variable. The default name is "Kconfig". 95 96KBUILD_VERBOSE 97-------------- 98Set the kbuild verbosity. Can be assigned same values as "V=...". 99 100See make help for the full list. 101 102Setting "V=..." takes precedence over KBUILD_VERBOSE. 103 104KBUILD_EXTMOD 105------------- 106Set the directory to look for the kernel source when building external 107modules. 108 109Setting "M=..." takes precedence over KBUILD_EXTMOD. 110 111KBUILD_OUTPUT 112------------- 113Specify the output directory when building the kernel. 114 115The output directory can also be specified using "O=...". 116 117Setting "O=..." takes precedence over KBUILD_OUTPUT. 118 119KBUILD_EXTRA_WARN 120----------------- 121Specify the extra build checks. The same value can be assigned by passing 122W=... from the command line. 123 124See `make help` for the list of the supported values. 125 126Setting "W=..." takes precedence over KBUILD_EXTRA_WARN. 127 128KBUILD_DEBARCH 129-------------- 130For the deb-pkg target, allows overriding the normal heuristics deployed by 131deb-pkg. Normally deb-pkg attempts to guess the right architecture based on 132the UTS_MACHINE variable, and on some architectures also the kernel config. 133The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian 134architecture. 135 136ARCH 137---- 138Set ARCH to the architecture to be built. 139 140In most cases the name of the architecture is the same as the 141directory name found in the arch/ directory. 142 143But some architectures such as x86 and sparc have aliases. 144 145- x86: i386 for 32 bit, x86_64 for 64 bit 146- sh: sh for 32 bit, sh64 for 64 bit 147- sparc: sparc32 for 32 bit, sparc64 for 64 bit 148 149CROSS_COMPILE 150------------- 151Specify an optional fixed part of the binutils filename. 152CROSS_COMPILE can be a part of the filename or the full path. 153 154CROSS_COMPILE is also used for ccache in some setups. 155 156CF 157-- 158Additional options for sparse. 159 160CF is often used on the command-line like this:: 161 162 make CF=-Wbitwise C=2 163 164INSTALL_PATH 165------------ 166INSTALL_PATH specifies where to place the updated kernel and system map 167images. Default is /boot, but you can set it to other values. 168 169INSTALLKERNEL 170------------- 171Install script called when using "make install". 172The default name is "installkernel". 173 174The script will be called with the following arguments: 175 176 - $1 - kernel version 177 - $2 - kernel image file 178 - $3 - kernel map file 179 - $4 - default install path (use root directory if blank) 180 181The implementation of "make install" is architecture specific 182and it may differ from the above. 183 184INSTALLKERNEL is provided to enable the possibility to 185specify a custom installer when cross compiling a kernel. 186 187MODLIB 188------ 189Specify where to install modules. 190The default value is:: 191 192 $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE) 193 194The value can be overridden in which case the default value is ignored. 195 196INSTALL_MOD_PATH 197---------------- 198INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory 199relocations required by build roots. This is not defined in the 200makefile but the argument can be passed to make if needed. 201 202INSTALL_MOD_STRIP 203----------------- 204INSTALL_MOD_STRIP, if defined, will cause modules to be 205stripped after they are installed. If INSTALL_MOD_STRIP is '1', then 206the default option --strip-debug will be used. Otherwise, 207INSTALL_MOD_STRIP value will be used as the options to the strip command. 208 209INSTALL_HDR_PATH 210---------------- 211INSTALL_HDR_PATH specifies where to install user space headers when 212executing "make headers_*". 213 214The default value is:: 215 216 $(objtree)/usr 217 218$(objtree) is the directory where output files are saved. 219The output directory is often set using "O=..." on the commandline. 220 221The value can be overridden in which case the default value is ignored. 222 223KBUILD_ABS_SRCTREE 224-------------------------------------------------- 225Kbuild uses a relative path to point to the tree when possible. For instance, 226when building in the source tree, the source tree path is '.' 227 228Setting this flag requests Kbuild to use absolute path to the source tree. 229There are some useful cases to do so, like when generating tag files with 230absolute path entries etc. 231 232KBUILD_SIGN_PIN 233--------------- 234This variable allows a passphrase or PIN to be passed to the sign-file 235utility when signing kernel modules, if the private key requires such. 236 237KBUILD_MODPOST_WARN 238------------------- 239KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined 240symbols in the final module linking stage. It changes such errors 241into warnings. 242 243KBUILD_MODPOST_NOFINAL 244---------------------- 245KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules. 246This is solely useful to speed up test compiles. 247 248KBUILD_EXTRA_SYMBOLS 249-------------------- 250For modules that use symbols from other modules. 251See more details in modules.rst. 252 253ALLSOURCE_ARCHS 254--------------- 255For tags/TAGS/cscope targets, you can specify more than one arch 256to be included in the databases, separated by blank space. E.g.:: 257 258 $ make ALLSOURCE_ARCHS="x86 mips arm" tags 259 260To get all available archs you can also specify all. E.g.:: 261 262 $ make ALLSOURCE_ARCHS=all tags 263 264KBUILD_BUILD_TIMESTAMP 265---------------------- 266Setting this to a date string overrides the timestamp used in the 267UTS_VERSION definition (uname -v in the running kernel). The value has to 268be a string that can be passed to date -d. The default value 269is the output of the date command at one point during build. 270 271KBUILD_BUILD_USER, KBUILD_BUILD_HOST 272------------------------------------ 273These two variables allow to override the user@host string displayed during 274boot and in /proc/version. The default value is the output of the commands 275whoami and host, respectively. 276 277LLVM 278---- 279If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead 280of GCC and GNU binutils to build the kernel. 281