Commit | Line | Data |
---|---|---|
cd238eff | 1 | ====================== |
1da177e4 | 2 | Linux Kernel Makefiles |
cd238eff | 3 | ====================== |
1da177e4 LT |
4 | |
5 | This document describes the Linux kernel Makefiles. | |
6 | ||
cd238eff | 7 | .. Table of Contents |
1da177e4 LT |
8 | |
9 | === 1 Overview | |
10 | === 2 Who does what | |
11 | === 3 The kbuild files | |
12 | --- 3.1 Goal definitions | |
13 | --- 3.2 Built-in object goals - obj-y | |
14 | --- 3.3 Loadable module goals - obj-m | |
15 | --- 3.4 Objects which export symbols | |
16 | --- 3.5 Library file goals - lib-y | |
17 | --- 3.6 Descending down in directories | |
18 | --- 3.7 Compilation flags | |
19 | --- 3.8 Command line dependency | |
20 | --- 3.9 Dependency tracking | |
21 | --- 3.10 Special Rules | |
20a468b5 | 22 | --- 3.11 $(CC) support functions |
691ef3e7 | 23 | --- 3.12 $(LD) support functions |
1da177e4 LT |
24 | |
25 | === 4 Host Program support | |
26 | --- 4.1 Simple Host Program | |
27 | --- 4.2 Composite Host Programs | |
62e22107 MY |
28 | --- 4.3 Using C++ for host programs |
29 | --- 4.4 Controlling compiler options for host programs | |
30 | --- 4.5 When host programs are actually built | |
31 | --- 4.6 Using hostprogs-$(CONFIG_FOO) | |
1da177e4 LT |
32 | |
33 | === 5 Kbuild clean infrastructure | |
34 | ||
35 | === 6 Architecture Makefiles | |
36 | --- 6.1 Set variables to tweak the build to the architecture | |
052ad274 PA |
37 | --- 6.2 Add prerequisites to archheaders: |
38 | --- 6.3 Add prerequisites to archprepare: | |
39 | --- 6.4 List directories to visit when descending | |
40 | --- 6.5 Architecture-specific boot images | |
41 | --- 6.6 Building non-kbuild targets | |
42 | --- 6.7 Commands useful for building a boot image | |
43 | --- 6.8 Custom kbuild commands | |
44 | --- 6.9 Preprocessing linker scripts | |
45 | --- 6.10 Generic header files | |
fbe6e37d | 46 | --- 6.11 Post-link pass |
1da177e4 | 47 | |
c7bb349e | 48 | === 7 Kbuild syntax for exported headers |
fcc8487d | 49 | --- 7.1 no-export-headers |
ae3f4151 MY |
50 | --- 7.2 generic-y |
51 | --- 7.3 generated-y | |
52 | --- 7.4 mandatory-y | |
c7bb349e SR |
53 | |
54 | === 8 Kbuild Variables | |
55 | === 9 Makefile language | |
56 | === 10 Credits | |
57 | === 11 TODO | |
1da177e4 | 58 | |
cd238eff MCC |
59 | 1 Overview |
60 | ========== | |
1da177e4 | 61 | |
cd238eff | 62 | The Makefiles have five parts:: |
1da177e4 LT |
63 | |
64 | Makefile the top Makefile. | |
65 | .config the kernel configuration file. | |
66 | arch/$(ARCH)/Makefile the arch Makefile. | |
67 | scripts/Makefile.* common rules etc. for all kbuild Makefiles. | |
68 | kbuild Makefiles there are about 500 of these. | |
69 | ||
70 | The top Makefile reads the .config file, which comes from the kernel | |
71 | configuration process. | |
72 | ||
73 | The top Makefile is responsible for building two major products: vmlinux | |
74 | (the resident kernel image) and modules (any module files). | |
75 | It builds these goals by recursively descending into the subdirectories of | |
76 | the kernel source tree. | |
77 | The list of subdirectories which are visited depends upon the kernel | |
78 | configuration. The top Makefile textually includes an arch Makefile | |
79 | with the name arch/$(ARCH)/Makefile. The arch Makefile supplies | |
80 | architecture-specific information to the top Makefile. | |
81 | ||
82 | Each subdirectory has a kbuild Makefile which carries out the commands | |
83 | passed down from above. The kbuild Makefile uses information from the | |
39e6e9cf | 84 | .config file to construct various file lists used by kbuild to build |
1da177e4 LT |
85 | any built-in or modular targets. |
86 | ||
87 | scripts/Makefile.* contains all the definitions/rules etc. that | |
88 | are used to build the kernel based on the kbuild makefiles. | |
89 | ||
90 | ||
cd238eff MCC |
91 | 2 Who does what |
92 | =============== | |
1da177e4 LT |
93 | |
94 | People have four different relationships with the kernel Makefiles. | |
95 | ||
96 | *Users* are people who build kernels. These people type commands such as | |
97 | "make menuconfig" or "make". They usually do not read or edit | |
98 | any kernel Makefiles (or any other source files). | |
99 | ||
100 | *Normal developers* are people who work on features such as device | |
101 | drivers, file systems, and network protocols. These people need to | |
a07f6033 | 102 | maintain the kbuild Makefiles for the subsystem they are |
1da177e4 LT |
103 | working on. In order to do this effectively, they need some overall |
104 | knowledge about the kernel Makefiles, plus detailed knowledge about the | |
105 | public interface for kbuild. | |
106 | ||
107 | *Arch developers* are people who work on an entire architecture, such | |
108 | as sparc or ia64. Arch developers need to know about the arch Makefile | |
109 | as well as kbuild Makefiles. | |
110 | ||
111 | *Kbuild developers* are people who work on the kernel build system itself. | |
112 | These people need to know about all aspects of the kernel Makefiles. | |
113 | ||
114 | This document is aimed towards normal developers and arch developers. | |
115 | ||
116 | ||
cd238eff MCC |
117 | 3 The kbuild files |
118 | ================== | |
1da177e4 LT |
119 | |
120 | Most Makefiles within the kernel are kbuild Makefiles that use the | |
a07f6033 | 121 | kbuild infrastructure. This chapter introduces the syntax used in the |
1da177e4 | 122 | kbuild makefiles. |
172c3ae3 | 123 | The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can |
a07f6033 | 124 | be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild' |
172c3ae3 | 125 | file will be used. |
1da177e4 LT |
126 | |
127 | Section 3.1 "Goal definitions" is a quick intro, further chapters provide | |
128 | more details, with real examples. | |
129 | ||
cd238eff MCC |
130 | 3.1 Goal definitions |
131 | -------------------- | |
1da177e4 LT |
132 | |
133 | Goal definitions are the main part (heart) of the kbuild Makefile. | |
134 | These lines define the files to be built, any special compilation | |
135 | options, and any subdirectories to be entered recursively. | |
136 | ||
137 | The most simple kbuild makefile contains one line: | |
138 | ||
cd238eff MCC |
139 | Example:: |
140 | ||
1da177e4 LT |
141 | obj-y += foo.o |
142 | ||
5c811e59 | 143 | This tells kbuild that there is one object in that directory, named |
1da177e4 LT |
144 | foo.o. foo.o will be built from foo.c or foo.S. |
145 | ||
146 | If foo.o shall be built as a module, the variable obj-m is used. | |
147 | Therefore the following pattern is often used: | |
148 | ||
cd238eff MCC |
149 | Example:: |
150 | ||
1da177e4 LT |
151 | obj-$(CONFIG_FOO) += foo.o |
152 | ||
153 | $(CONFIG_FOO) evaluates to either y (for built-in) or m (for module). | |
154 | If CONFIG_FOO is neither y nor m, then the file will not be compiled | |
155 | nor linked. | |
156 | ||
cd238eff MCC |
157 | 3.2 Built-in object goals - obj-y |
158 | --------------------------------- | |
1da177e4 LT |
159 | |
160 | The kbuild Makefile specifies object files for vmlinux | |
a07f6033 | 161 | in the $(obj-y) lists. These lists depend on the kernel |
1da177e4 LT |
162 | configuration. |
163 | ||
164 | Kbuild compiles all the $(obj-y) files. It then calls | |
f49821ee | 165 | "$(AR) rcSTP" to merge these files into one built-in.a file. |
dee94953 MY |
166 | This is a thin archive without a symbol table. It will be later |
167 | linked into vmlinux by scripts/link-vmlinux.sh | |
1da177e4 LT |
168 | |
169 | The order of files in $(obj-y) is significant. Duplicates in | |
170 | the lists are allowed: the first instance will be linked into | |
f49821ee | 171 | built-in.a and succeeding instances will be ignored. |
1da177e4 LT |
172 | |
173 | Link order is significant, because certain functions | |
174 | (module_init() / __initcall) will be called during boot in the | |
175 | order they appear. So keep in mind that changing the link | |
a07f6033 JE |
176 | order may e.g. change the order in which your SCSI |
177 | controllers are detected, and thus your disks are renumbered. | |
1da177e4 | 178 | |
cd238eff MCC |
179 | Example:: |
180 | ||
1da177e4 LT |
181 | #drivers/isdn/i4l/Makefile |
182 | # Makefile for the kernel ISDN subsystem and device drivers. | |
183 | # Each configuration option enables a list of files. | |
2f5a2f81 | 184 | obj-$(CONFIG_ISDN_I4L) += isdn.o |
1da177e4 LT |
185 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o |
186 | ||
cd238eff MCC |
187 | 3.3 Loadable module goals - obj-m |
188 | --------------------------------- | |
1da177e4 | 189 | |
39fed701 | 190 | $(obj-m) specifies object files which are built as loadable |
1da177e4 LT |
191 | kernel modules. |
192 | ||
193 | A module may be built from one source file or several source | |
194 | files. In the case of one source file, the kbuild makefile | |
195 | simply adds the file to $(obj-m). | |
196 | ||
cd238eff MCC |
197 | Example:: |
198 | ||
1da177e4 LT |
199 | #drivers/isdn/i4l/Makefile |
200 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o | |
201 | ||
202 | Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm' | |
203 | ||
204 | If a kernel module is built from several source files, you specify | |
4f827280 MM |
205 | that you want to build a module in the same way as above; however, |
206 | kbuild needs to know which object files you want to build your | |
207 | module from, so you have to tell it by setting a $(<module_name>-y) | |
208 | variable. | |
1da177e4 | 209 | |
cd238eff MCC |
210 | Example:: |
211 | ||
1da177e4 | 212 | #drivers/isdn/i4l/Makefile |
4f827280 MM |
213 | obj-$(CONFIG_ISDN_I4L) += isdn.o |
214 | isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o | |
1da177e4 LT |
215 | |
216 | In this example, the module name will be isdn.o. Kbuild will | |
4f827280 | 217 | compile the objects listed in $(isdn-y) and then run |
1da177e4 LT |
218 | "$(LD) -r" on the list of these files to generate isdn.o. |
219 | ||
4f827280 | 220 | Due to kbuild recognizing $(<module_name>-y) for composite objects, |
cd238eff | 221 | you can use the value of a `CONFIG_` symbol to optionally include an |
4f827280 | 222 | object file as part of a composite object. |
1da177e4 | 223 | |
cd238eff MCC |
224 | Example:: |
225 | ||
1da177e4 | 226 | #fs/ext2/Makefile |
4f827280 MM |
227 | obj-$(CONFIG_EXT2_FS) += ext2.o |
228 | ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \ | |
229 | namei.o super.o symlink.o | |
230 | ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \ | |
231 | xattr_trusted.o | |
232 | ||
233 | In this example, xattr.o, xattr_user.o and xattr_trusted.o are only | |
234 | part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR) | |
235 | evaluates to 'y'. | |
1da177e4 LT |
236 | |
237 | Note: Of course, when you are building objects into the kernel, | |
238 | the syntax above will also work. So, if you have CONFIG_EXT2_FS=y, | |
239 | kbuild will build an ext2.o file for you out of the individual | |
f49821ee | 240 | parts and then link this into built-in.a, as you would expect. |
1da177e4 | 241 | |
cd238eff MCC |
242 | 3.4 Objects which export symbols |
243 | -------------------------------- | |
1da177e4 LT |
244 | |
245 | No special notation is required in the makefiles for | |
246 | modules exporting symbols. | |
247 | ||
cd238eff MCC |
248 | 3.5 Library file goals - lib-y |
249 | ------------------------------ | |
1da177e4 | 250 | |
a07f6033 | 251 | Objects listed with obj-* are used for modules, or |
f49821ee | 252 | combined in a built-in.a for that specific directory. |
1da177e4 LT |
253 | There is also the possibility to list objects that will |
254 | be included in a library, lib.a. | |
255 | All objects listed with lib-y are combined in a single | |
256 | library for that directory. | |
5d3f083d ML |
257 | Objects that are listed in obj-y and additionally listed in |
258 | lib-y will not be included in the library, since they will | |
259 | be accessible anyway. | |
a07f6033 | 260 | For consistency, objects listed in lib-m will be included in lib.a. |
1da177e4 LT |
261 | |
262 | Note that the same kbuild makefile may list files to be built-in | |
263 | and to be part of a library. Therefore the same directory | |
f49821ee | 264 | may contain both a built-in.a and a lib.a file. |
1da177e4 | 265 | |
cd238eff MCC |
266 | Example:: |
267 | ||
2f5a2f81 MM |
268 | #arch/x86/lib/Makefile |
269 | lib-y := delay.o | |
1da177e4 | 270 | |
2f5a2f81 MM |
271 | This will create a library lib.a based on delay.o. For kbuild to |
272 | actually recognize that there is a lib.a being built, the directory | |
273 | shall be listed in libs-y. | |
cd238eff | 274 | |
052ad274 | 275 | See also "6.4 List directories to visit when descending". |
39e6e9cf | 276 | |
cd238eff | 277 | Use of lib-y is normally restricted to `lib/` and `arch/*/lib`. |
1da177e4 | 278 | |
cd238eff MCC |
279 | 3.6 Descending down in directories |
280 | ---------------------------------- | |
1da177e4 LT |
281 | |
282 | A Makefile is only responsible for building objects in its own | |
283 | directory. Files in subdirectories should be taken care of by | |
284 | Makefiles in these subdirs. The build system will automatically | |
285 | invoke make recursively in subdirectories, provided you let it know of | |
286 | them. | |
287 | ||
a07f6033 | 288 | To do so, obj-y and obj-m are used. |
1da177e4 LT |
289 | ext2 lives in a separate directory, and the Makefile present in fs/ |
290 | tells kbuild to descend down using the following assignment. | |
291 | ||
cd238eff MCC |
292 | Example:: |
293 | ||
1da177e4 LT |
294 | #fs/Makefile |
295 | obj-$(CONFIG_EXT2_FS) += ext2/ | |
296 | ||
297 | If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular) | |
298 | the corresponding obj- variable will be set, and kbuild will descend | |
299 | down in the ext2 directory. | |
300 | Kbuild only uses this information to decide that it needs to visit | |
301 | the directory, it is the Makefile in the subdirectory that | |
39fed701 | 302 | specifies what is modular and what is built-in. |
1da177e4 | 303 | |
cd238eff | 304 | It is good practice to use a `CONFIG_` variable when assigning directory |
1da177e4 | 305 | names. This allows kbuild to totally skip the directory if the |
cd238eff | 306 | corresponding `CONFIG_` option is neither 'y' nor 'm'. |
1da177e4 | 307 | |
cd238eff MCC |
308 | 3.7 Compilation flags |
309 | --------------------- | |
1da177e4 | 310 | |
f77bf014 | 311 | ccflags-y, asflags-y and ldflags-y |
c95940f2 NK |
312 | These three flags apply only to the kbuild makefile in which they |
313 | are assigned. They are used for all the normal cc, as and ld | |
314 | invocations happening during a recursive build. | |
f77bf014 | 315 | Note: Flags with the same behaviour were previously named: |
c95940f2 NK |
316 | EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS. |
317 | They are still supported but their usage is deprecated. | |
1da177e4 | 318 | |
eb07e1b4 | 319 | ccflags-y specifies options for compiling with $(CC). |
1da177e4 | 320 | |
cd238eff MCC |
321 | Example:: |
322 | ||
3d91a353 SD |
323 | # drivers/acpi/acpica/Makefile |
324 | ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA | |
325 | ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT | |
1da177e4 LT |
326 | |
327 | This variable is necessary because the top Makefile owns the | |
a0f97e06 | 328 | variable $(KBUILD_CFLAGS) and uses it for compilation flags for the |
1da177e4 LT |
329 | entire tree. |
330 | ||
5ef87263 | 331 | asflags-y specifies assembler options. |
1da177e4 | 332 | |
cd238eff MCC |
333 | Example:: |
334 | ||
eb07e1b4 MM |
335 | #arch/sparc/kernel/Makefile |
336 | asflags-y := -ansi | |
1da177e4 | 337 | |
eb07e1b4 | 338 | ldflags-y specifies options for linking with $(LD). |
1da177e4 | 339 | |
cd238eff MCC |
340 | Example:: |
341 | ||
eb07e1b4 MM |
342 | #arch/cris/boot/compressed/Makefile |
343 | ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds | |
1da177e4 | 344 | |
720097d8 | 345 | subdir-ccflags-y, subdir-asflags-y |
eb07e1b4 | 346 | The two flags listed above are similar to ccflags-y and asflags-y. |
c95940f2 NK |
347 | The difference is that the subdir- variants have effect for the kbuild |
348 | file where they are present and all subdirectories. | |
349 | Options specified using subdir-* are added to the commandline before | |
350 | the options specified using the non-subdir variants. | |
720097d8 | 351 | |
cd238eff MCC |
352 | Example:: |
353 | ||
720097d8 SR |
354 | subdir-ccflags-y := -Werror |
355 | ||
1da177e4 | 356 | CFLAGS_$@, AFLAGS_$@ |
1da177e4 LT |
357 | CFLAGS_$@ and AFLAGS_$@ only apply to commands in current |
358 | kbuild makefile. | |
359 | ||
360 | $(CFLAGS_$@) specifies per-file options for $(CC). The $@ | |
361 | part has a literal value which specifies the file that it is for. | |
362 | ||
cd238eff MCC |
363 | Example:: |
364 | ||
1da177e4 LT |
365 | # drivers/scsi/Makefile |
366 | CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF | |
367 | CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \ | |
368 | -DGDTH_STATISTICS | |
1da177e4 | 369 | |
eb07e1b4 | 370 | These two lines specify compilation flags for aha152x.o and gdth.o. |
1da177e4 LT |
371 | |
372 | $(AFLAGS_$@) is a similar feature for source files in assembly | |
373 | languages. | |
374 | ||
cd238eff MCC |
375 | Example:: |
376 | ||
1da177e4 | 377 | # arch/arm/kernel/Makefile |
eb07e1b4 MM |
378 | AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) |
379 | AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312 | |
380 | AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt | |
381 | ||
1da177e4 | 382 | |
cd238eff MCC |
383 | 3.9 Dependency tracking |
384 | ----------------------- | |
1da177e4 LT |
385 | |
386 | Kbuild tracks dependencies on the following: | |
16886949 | 387 | |
cd238eff MCC |
388 | 1) All prerequisite files (both `*.c` and `*.h`) |
389 | 2) `CONFIG_` options used in all prerequisite files | |
1da177e4 LT |
390 | 3) Command-line used to compile target |
391 | ||
392 | Thus, if you change an option to $(CC) all affected files will | |
393 | be re-compiled. | |
394 | ||
cd238eff MCC |
395 | 3.10 Special Rules |
396 | ------------------ | |
1da177e4 LT |
397 | |
398 | Special rules are used when the kbuild infrastructure does | |
399 | not provide the required support. A typical example is | |
400 | header files generated during the build process. | |
5c811e59 | 401 | Another example are the architecture-specific Makefiles which |
a07f6033 | 402 | need special rules to prepare boot images etc. |
1da177e4 LT |
403 | |
404 | Special rules are written as normal Make rules. | |
405 | Kbuild is not executing in the directory where the Makefile is | |
406 | located, so all special rules shall provide a relative | |
407 | path to prerequisite files and target files. | |
408 | ||
409 | Two variables are used when defining special rules: | |
410 | ||
cd238eff MCC |
411 | $(src) |
412 | $(src) is a relative path which points to the directory | |
413 | where the Makefile is located. Always use $(src) when | |
414 | referring to files located in the src tree. | |
415 | ||
416 | $(obj) | |
417 | $(obj) is a relative path which points to the directory | |
418 | where the target is saved. Always use $(obj) when | |
419 | referring to generated files. | |
1da177e4 | 420 | |
cd238eff | 421 | Example:: |
1da177e4 | 422 | |
1da177e4 LT |
423 | #drivers/scsi/Makefile |
424 | $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl | |
425 | $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl | |
426 | ||
cd238eff MCC |
427 | This is a special rule, following the normal syntax |
428 | required by make. | |
429 | ||
430 | The target file depends on two prerequisite files. References | |
431 | to the target file are prefixed with $(obj), references | |
432 | to prerequisites are referenced with $(src) (because they are not | |
433 | generated files). | |
434 | ||
435 | $(kecho) | |
436 | echoing information to user in a rule is often a good practice | |
437 | but when execution "make -s" one does not expect to see any output | |
438 | except for warnings/errors. | |
439 | To support this kbuild defines $(kecho) which will echo out the | |
440 | text following $(kecho) to stdout except if "make -s" is used. | |
441 | ||
442 | Example:: | |
443 | ||
5410ecc0 MF |
444 | #arch/blackfin/boot/Makefile |
445 | $(obj)/vmImage: $(obj)/vmlinux.gz | |
446 | $(call if_changed,uimage) | |
447 | @$(kecho) 'Kernel: $@ is ready' | |
448 | ||
449 | ||
cd238eff MCC |
450 | 3.11 $(CC) support functions |
451 | ---------------------------- | |
20a468b5 | 452 | |
a07f6033 | 453 | The kernel may be built with several different versions of |
20a468b5 | 454 | $(CC), each supporting a unique set of features and options. |
39fed701 | 455 | kbuild provides basic support to check for valid options for $(CC). |
e95be9a5 | 456 | $(CC) is usually the gcc compiler, but other alternatives are |
20a468b5 SR |
457 | available. |
458 | ||
459 | as-option | |
a07f6033 | 460 | as-option is used to check if $(CC) -- when used to compile |
cd238eff | 461 | assembler (`*.S`) files -- supports the given option. An optional |
a07f6033 | 462 | second option may be specified if the first option is not supported. |
20a468b5 | 463 | |
cd238eff MCC |
464 | Example:: |
465 | ||
20a468b5 SR |
466 | #arch/sh/Makefile |
467 | cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),) | |
468 | ||
a07f6033 | 469 | In the above example, cflags-y will be assigned the option |
20a468b5 SR |
470 | -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC). |
471 | The second argument is optional, and if supplied will be used | |
cd238eff MCC |
472 | if first argument is not supported. |
473 | ||
e2414910 AK |
474 | as-instr |
475 | as-instr checks if the assembler reports a specific instruction | |
476 | and then outputs either option1 or option2 | |
477 | C escapes are supported in the test instruction | |
5ef87263 | 478 | Note: as-instr-option uses KBUILD_AFLAGS for assembler options |
e2414910 | 479 | |
20a468b5 | 480 | cc-option |
39fed701 GU |
481 | cc-option is used to check if $(CC) supports a given option, and if |
482 | not supported to use an optional second option. | |
20a468b5 | 483 | |
cd238eff MCC |
484 | Example:: |
485 | ||
25eb650a | 486 | #arch/x86/Makefile |
20a468b5 SR |
487 | cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) |
488 | ||
5c811e59 | 489 | In the above example, cflags-y will be assigned the option |
a07f6033 JE |
490 | -march=pentium-mmx if supported by $(CC), otherwise -march=i586. |
491 | The second argument to cc-option is optional, and if omitted, | |
20a468b5 | 492 | cflags-y will be assigned no value if first option is not supported. |
a0f97e06 | 493 | Note: cc-option uses KBUILD_CFLAGS for $(CC) options |
20a468b5 SR |
494 | |
495 | cc-option-yn | |
39e6e9cf | 496 | cc-option-yn is used to check if gcc supports a given option |
20a468b5 SR |
497 | and return 'y' if supported, otherwise 'n'. |
498 | ||
cd238eff MCC |
499 | Example:: |
500 | ||
20a468b5 SR |
501 | #arch/ppc/Makefile |
502 | biarch := $(call cc-option-yn, -m32) | |
503 | aflags-$(biarch) += -a32 | |
504 | cflags-$(biarch) += -m32 | |
39e6e9cf | 505 | |
a07f6033 JE |
506 | In the above example, $(biarch) is set to y if $(CC) supports the -m32 |
507 | option. When $(biarch) equals 'y', the expanded variables $(aflags-y) | |
508 | and $(cflags-y) will be assigned the values -a32 and -m32, | |
509 | respectively. | |
a0f97e06 | 510 | Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options |
20a468b5 | 511 | |
8417da6f MM |
512 | cc-disable-warning |
513 | cc-disable-warning checks if gcc supports a given warning and returns | |
514 | the commandline switch to disable it. This special function is needed, | |
515 | because gcc 4.4 and later accept any unknown -Wno-* option and only | |
516 | warn about it if there is another warning in the source file. | |
517 | ||
cd238eff MCC |
518 | Example:: |
519 | ||
8417da6f MM |
520 | KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) |
521 | ||
522 | In the above example, -Wno-unused-but-set-variable will be added to | |
523 | KBUILD_CFLAGS only if gcc really accepts it. | |
524 | ||
20a468b5 | 525 | cc-ifversion |
6dcb4e5e MY |
526 | cc-ifversion tests the version of $(CC) and equals the fourth parameter |
527 | if version expression is true, or the fifth (if given) if the version | |
528 | expression is false. | |
20a468b5 | 529 | |
cd238eff MCC |
530 | Example:: |
531 | ||
20a468b5 | 532 | #fs/reiserfs/Makefile |
f77bf014 | 533 | ccflags-y := $(call cc-ifversion, -lt, 0402, -O1) |
20a468b5 | 534 | |
f77bf014 | 535 | In this example, ccflags-y will be assigned the value -O1 if the |
20a468b5 | 536 | $(CC) version is less than 4.2. |
39e6e9cf | 537 | cc-ifversion takes all the shell operators: |
20a468b5 SR |
538 | -eq, -ne, -lt, -le, -gt, and -ge |
539 | The third parameter may be a text as in this example, but it may also | |
540 | be an expanded variable or a macro. | |
541 | ||
910b4046 | 542 | cc-cross-prefix |
631bcfbb | 543 | cc-cross-prefix is used to check if there exists a $(CC) in path with |
910b4046 SR |
544 | one of the listed prefixes. The first prefix where there exist a |
545 | prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found | |
546 | then nothing is returned. | |
547 | Additional prefixes are separated by a single space in the | |
548 | call of cc-cross-prefix. | |
631bcfbb GU |
549 | This functionality is useful for architecture Makefiles that try |
550 | to set CROSS_COMPILE to well-known values but may have several | |
910b4046 | 551 | values to select between. |
631bcfbb GU |
552 | It is recommended only to try to set CROSS_COMPILE if it is a cross |
553 | build (host arch is different from target arch). And if CROSS_COMPILE | |
910b4046 SR |
554 | is already set then leave it with the old value. |
555 | ||
cd238eff MCC |
556 | Example:: |
557 | ||
910b4046 SR |
558 | #arch/m68k/Makefile |
559 | ifneq ($(SUBARCH),$(ARCH)) | |
560 | ifeq ($(CROSS_COMPILE),) | |
561 | CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-) | |
562 | endif | |
563 | endif | |
564 | ||
cd238eff MCC |
565 | 3.12 $(LD) support functions |
566 | ---------------------------- | |
691ef3e7 SR |
567 | |
568 | ld-option | |
569 | ld-option is used to check if $(LD) supports the supplied option. | |
570 | ld-option takes two options as arguments. | |
571 | The second argument is an optional option that can be used if the | |
572 | first option is not supported by $(LD). | |
573 | ||
cd238eff MCC |
574 | Example:: |
575 | ||
691ef3e7 | 576 | #Makefile |
5b83df2b | 577 | LDFLAGS_vmlinux += $(call ld-option, -X) |
691ef3e7 SR |
578 | |
579 | ||
cd238eff MCC |
580 | 4 Host Program support |
581 | ====================== | |
1da177e4 LT |
582 | |
583 | Kbuild supports building executables on the host for use during the | |
584 | compilation stage. | |
585 | Two steps are required in order to use a host executable. | |
586 | ||
587 | The first step is to tell kbuild that a host program exists. This is | |
588 | done utilising the variable hostprogs-y. | |
589 | ||
590 | The second step is to add an explicit dependency to the executable. | |
39e6e9cf | 591 | This can be done in two ways. Either add the dependency in a rule, |
1da177e4 LT |
592 | or utilise the variable $(always). |
593 | Both possibilities are described in the following. | |
594 | ||
cd238eff MCC |
595 | 4.1 Simple Host Program |
596 | ----------------------- | |
1da177e4 LT |
597 | |
598 | In some cases there is a need to compile and run a program on the | |
599 | computer where the build is running. | |
600 | The following line tells kbuild that the program bin2hex shall be | |
601 | built on the build host. | |
602 | ||
cd238eff MCC |
603 | Example:: |
604 | ||
1da177e4 LT |
605 | hostprogs-y := bin2hex |
606 | ||
607 | Kbuild assumes in the above example that bin2hex is made from a single | |
608 | c-source file named bin2hex.c located in the same directory as | |
609 | the Makefile. | |
39e6e9cf | 610 | |
cd238eff MCC |
611 | 4.2 Composite Host Programs |
612 | --------------------------- | |
1da177e4 LT |
613 | |
614 | Host programs can be made up based on composite objects. | |
615 | The syntax used to define composite objects for host programs is | |
616 | similar to the syntax used for kernel objects. | |
5d3f083d | 617 | $(<executable>-objs) lists all objects used to link the final |
1da177e4 LT |
618 | executable. |
619 | ||
cd238eff MCC |
620 | Example:: |
621 | ||
1da177e4 | 622 | #scripts/lxdialog/Makefile |
39e6e9cf | 623 | hostprogs-y := lxdialog |
1da177e4 LT |
624 | lxdialog-objs := checklist.o lxdialog.o |
625 | ||
626 | Objects with extension .o are compiled from the corresponding .c | |
a07f6033 | 627 | files. In the above example, checklist.c is compiled to checklist.o |
1da177e4 | 628 | and lxdialog.c is compiled to lxdialog.o. |
cd238eff | 629 | |
a07f6033 | 630 | Finally, the two .o files are linked to the executable, lxdialog. |
1da177e4 LT |
631 | Note: The syntax <executable>-y is not permitted for host-programs. |
632 | ||
cd238eff MCC |
633 | 4.3 Using C++ for host programs |
634 | ------------------------------- | |
1da177e4 LT |
635 | |
636 | kbuild offers support for host programs written in C++. This was | |
637 | introduced solely to support kconfig, and is not recommended | |
638 | for general use. | |
639 | ||
cd238eff MCC |
640 | Example:: |
641 | ||
1da177e4 LT |
642 | #scripts/kconfig/Makefile |
643 | hostprogs-y := qconf | |
644 | qconf-cxxobjs := qconf.o | |
645 | ||
646 | In the example above the executable is composed of the C++ file | |
647 | qconf.cc - identified by $(qconf-cxxobjs). | |
39e6e9cf | 648 | |
39fed701 | 649 | If qconf is composed of a mixture of .c and .cc files, then an |
1da177e4 LT |
650 | additional line can be used to identify this. |
651 | ||
cd238eff MCC |
652 | Example:: |
653 | ||
1da177e4 LT |
654 | #scripts/kconfig/Makefile |
655 | hostprogs-y := qconf | |
656 | qconf-cxxobjs := qconf.o | |
657 | qconf-objs := check.o | |
39e6e9cf | 658 | |
cd238eff MCC |
659 | 4.4 Controlling compiler options for host programs |
660 | -------------------------------------------------- | |
1da177e4 LT |
661 | |
662 | When compiling host programs, it is possible to set specific flags. | |
663 | The programs will always be compiled utilising $(HOSTCC) passed | |
96f14fe7 | 664 | the options specified in $(KBUILD_HOSTCFLAGS). |
1da177e4 | 665 | To set flags that will take effect for all host programs created |
a07f6033 | 666 | in that Makefile, use the variable HOST_EXTRACFLAGS. |
1da177e4 | 667 | |
cd238eff MCC |
668 | Example:: |
669 | ||
1da177e4 LT |
670 | #scripts/lxdialog/Makefile |
671 | HOST_EXTRACFLAGS += -I/usr/include/ncurses | |
39e6e9cf | 672 | |
1da177e4 LT |
673 | To set specific flags for a single file the following construction |
674 | is used: | |
675 | ||
cd238eff MCC |
676 | Example:: |
677 | ||
1da177e4 LT |
678 | #arch/ppc64/boot/Makefile |
679 | HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE) | |
39e6e9cf | 680 | |
1da177e4 | 681 | It is also possible to specify additional options to the linker. |
39e6e9cf | 682 | |
cd238eff MCC |
683 | Example:: |
684 | ||
1da177e4 | 685 | #scripts/kconfig/Makefile |
c86b1f93 | 686 | HOSTLDLIBS_qconf := -L$(QTDIR)/lib |
1da177e4 | 687 | |
a07f6033 JE |
688 | When linking qconf, it will be passed the extra option |
689 | "-L$(QTDIR)/lib". | |
39e6e9cf | 690 | |
cd238eff MCC |
691 | 4.5 When host programs are actually built |
692 | ----------------------------------------- | |
1da177e4 LT |
693 | |
694 | Kbuild will only build host-programs when they are referenced | |
695 | as a prerequisite. | |
696 | This is possible in two ways: | |
697 | ||
698 | (1) List the prerequisite explicitly in a special rule. | |
699 | ||
cd238eff MCC |
700 | Example:: |
701 | ||
1da177e4 LT |
702 | #drivers/pci/Makefile |
703 | hostprogs-y := gen-devlist | |
704 | $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist | |
705 | ( cd $(obj); ./gen-devlist ) < $< | |
706 | ||
39e6e9cf | 707 | The target $(obj)/devlist.h will not be built before |
1da177e4 LT |
708 | $(obj)/gen-devlist is updated. Note that references to |
709 | the host programs in special rules must be prefixed with $(obj). | |
710 | ||
711 | (2) Use $(always) | |
cd238eff | 712 | |
1da177e4 LT |
713 | When there is no suitable special rule, and the host program |
714 | shall be built when a makefile is entered, the $(always) | |
715 | variable shall be used. | |
716 | ||
cd238eff MCC |
717 | Example:: |
718 | ||
1da177e4 LT |
719 | #scripts/lxdialog/Makefile |
720 | hostprogs-y := lxdialog | |
721 | always := $(hostprogs-y) | |
722 | ||
723 | This will tell kbuild to build lxdialog even if not referenced in | |
724 | any rule. | |
725 | ||
cd238eff MCC |
726 | 4.6 Using hostprogs-$(CONFIG_FOO) |
727 | --------------------------------- | |
1da177e4 | 728 | |
39e6e9cf | 729 | A typical pattern in a Kbuild file looks like this: |
1da177e4 | 730 | |
cd238eff MCC |
731 | Example:: |
732 | ||
1da177e4 LT |
733 | #scripts/Makefile |
734 | hostprogs-$(CONFIG_KALLSYMS) += kallsyms | |
735 | ||
736 | Kbuild knows about both 'y' for built-in and 'm' for module. | |
39fed701 | 737 | So if a config symbol evaluates to 'm', kbuild will still build |
a07f6033 JE |
738 | the binary. In other words, Kbuild handles hostprogs-m exactly |
739 | like hostprogs-y. But only hostprogs-y is recommended to be used | |
740 | when no CONFIG symbols are involved. | |
1da177e4 | 741 | |
cd238eff MCC |
742 | 5 Kbuild clean infrastructure |
743 | ============================= | |
1da177e4 | 744 | |
a07f6033 | 745 | "make clean" deletes most generated files in the obj tree where the kernel |
1da177e4 LT |
746 | is compiled. This includes generated files such as host programs. |
747 | Kbuild knows targets listed in $(hostprogs-y), $(hostprogs-m), $(always), | |
748 | $(extra-y) and $(targets). They are all deleted during "make clean". | |
749 | Files matching the patterns "*.[oas]", "*.ko", plus some additional files | |
750 | generated by kbuild are deleted all over the kernel src tree when | |
751 | "make clean" is executed. | |
752 | ||
1634f2bf MY |
753 | Additional files or directories can be specified in kbuild makefiles by use of |
754 | $(clean-files). | |
1da177e4 | 755 | |
cd238eff MCC |
756 | Example:: |
757 | ||
97659181 MM |
758 | #lib/Makefile |
759 | clean-files := crc32table.h | |
1da177e4 | 760 | |
bd55daf4 JR |
761 | When executing "make clean", the file "crc32table.h" will be deleted. |
762 | Kbuild will assume files to be in the same relative directory as the | |
97659181 | 763 | Makefile, except if prefixed with $(objtree). |
1da177e4 | 764 | |
1634f2bf MY |
765 | To exclude certain files or directories from make clean, use the |
766 | $(no-clean-files) variable. | |
ef8ff89b | 767 | |
1da177e4 LT |
768 | Usually kbuild descends down in subdirectories due to "obj-* := dir/", |
769 | but in the architecture makefiles where the kbuild infrastructure | |
770 | is not sufficient this sometimes needs to be explicit. | |
771 | ||
cd238eff MCC |
772 | Example:: |
773 | ||
25eb650a | 774 | #arch/x86/boot/Makefile |
1da177e4 LT |
775 | subdir- := compressed/ |
776 | ||
777 | The above assignment instructs kbuild to descend down in the | |
778 | directory compressed/ when "make clean" is executed. | |
779 | ||
39fed701 | 780 | To support the clean infrastructure in the Makefiles that build the |
1da177e4 LT |
781 | final bootimage there is an optional target named archclean: |
782 | ||
cd238eff MCC |
783 | Example:: |
784 | ||
25eb650a | 785 | #arch/x86/Makefile |
1da177e4 | 786 | archclean: |
25eb650a | 787 | $(Q)$(MAKE) $(clean)=arch/x86/boot |
1da177e4 | 788 | |
25eb650a WG |
789 | When "make clean" is executed, make will descend down in arch/x86/boot, |
790 | and clean as usual. The Makefile located in arch/x86/boot/ may use | |
1da177e4 LT |
791 | the subdir- trick to descend further down. |
792 | ||
793 | Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is | |
794 | included in the top level makefile, and the kbuild infrastructure | |
795 | is not operational at that point. | |
796 | ||
797 | Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will | |
798 | be visited during "make clean". | |
799 | ||
cd238eff MCC |
800 | 6 Architecture Makefiles |
801 | ======================== | |
1da177e4 LT |
802 | |
803 | The top level Makefile sets up the environment and does the preparation, | |
804 | before starting to descend down in the individual directories. | |
a07f6033 JE |
805 | The top level makefile contains the generic part, whereas |
806 | arch/$(ARCH)/Makefile contains what is required to set up kbuild | |
807 | for said architecture. | |
808 | To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines | |
1da177e4 LT |
809 | a few targets. |
810 | ||
a07f6033 | 811 | When kbuild executes, the following steps are followed (roughly): |
cd238eff | 812 | |
a07f6033 | 813 | 1) Configuration of the kernel => produce .config |
1da177e4 | 814 | 2) Store kernel version in include/linux/version.h |
b22ae40e | 815 | 3) Updating all other prerequisites to the target prepare: |
1da177e4 | 816 | - Additional prerequisites are specified in arch/$(ARCH)/Makefile |
b22ae40e | 817 | 4) Recursively descend down in all directories listed in |
1da177e4 | 818 | init-* core* drivers-* net-* libs-* and build all targets. |
a07f6033 | 819 | - The values of the above variables are expanded in arch/$(ARCH)/Makefile. |
b22ae40e | 820 | 5) All object files are then linked and the resulting file vmlinux is |
a07f6033 | 821 | located at the root of the obj tree. |
1da177e4 LT |
822 | The very first objects linked are listed in head-y, assigned by |
823 | arch/$(ARCH)/Makefile. | |
b22ae40e | 824 | 6) Finally, the architecture-specific part does any required post processing |
1da177e4 LT |
825 | and builds the final bootimage. |
826 | - This includes building boot records | |
5c811e59 | 827 | - Preparing initrd images and the like |
1da177e4 LT |
828 | |
829 | ||
cd238eff MCC |
830 | 6.1 Set variables to tweak the build to the architecture |
831 | -------------------------------------------------------- | |
1da177e4 | 832 | |
cd238eff MCC |
833 | LDFLAGS |
834 | Generic $(LD) options | |
1da177e4 LT |
835 | |
836 | Flags used for all invocations of the linker. | |
837 | Often specifying the emulation is sufficient. | |
838 | ||
cd238eff MCC |
839 | Example:: |
840 | ||
1da177e4 LT |
841 | #arch/s390/Makefile |
842 | LDFLAGS := -m elf_s390 | |
cd238eff | 843 | |
f77bf014 | 844 | Note: ldflags-y can be used to further customise |
a9af3305 | 845 | the flags used. See chapter 3.7. |
39e6e9cf | 846 | |
cd238eff MCC |
847 | LDFLAGS_vmlinux |
848 | Options for $(LD) when linking vmlinux | |
1da177e4 LT |
849 | |
850 | LDFLAGS_vmlinux is used to specify additional flags to pass to | |
a07f6033 | 851 | the linker when linking the final vmlinux image. |
1da177e4 LT |
852 | LDFLAGS_vmlinux uses the LDFLAGS_$@ support. |
853 | ||
cd238eff MCC |
854 | Example:: |
855 | ||
25eb650a | 856 | #arch/x86/Makefile |
1da177e4 LT |
857 | LDFLAGS_vmlinux := -e stext |
858 | ||
cd238eff MCC |
859 | OBJCOPYFLAGS |
860 | objcopy flags | |
1da177e4 LT |
861 | |
862 | When $(call if_changed,objcopy) is used to translate a .o file, | |
a07f6033 | 863 | the flags specified in OBJCOPYFLAGS will be used. |
1da177e4 LT |
864 | $(call if_changed,objcopy) is often used to generate raw binaries on |
865 | vmlinux. | |
866 | ||
cd238eff MCC |
867 | Example:: |
868 | ||
1da177e4 LT |
869 | #arch/s390/Makefile |
870 | OBJCOPYFLAGS := -O binary | |
871 | ||
872 | #arch/s390/boot/Makefile | |
873 | $(obj)/image: vmlinux FORCE | |
874 | $(call if_changed,objcopy) | |
875 | ||
a07f6033 | 876 | In this example, the binary $(obj)/image is a binary version of |
1da177e4 LT |
877 | vmlinux. The usage of $(call if_changed,xxx) will be described later. |
878 | ||
cd238eff | 879 | KBUILD_AFLAGS |
5ef87263 | 880 | Assembler flags |
1da177e4 LT |
881 | |
882 | Default value - see top level Makefile | |
883 | Append or modify as required per architecture. | |
884 | ||
cd238eff MCC |
885 | Example:: |
886 | ||
1da177e4 | 887 | #arch/sparc64/Makefile |
222d394d | 888 | KBUILD_AFLAGS += -m64 -mcpu=ultrasparc |
1da177e4 | 889 | |
cd238eff MCC |
890 | KBUILD_CFLAGS |
891 | $(CC) compiler flags | |
1da177e4 LT |
892 | |
893 | Default value - see top level Makefile | |
894 | Append or modify as required per architecture. | |
895 | ||
a0f97e06 | 896 | Often, the KBUILD_CFLAGS variable depends on the configuration. |
1da177e4 | 897 | |
cd238eff MCC |
898 | Example:: |
899 | ||
ff4eb04c PB |
900 | #arch/x86/boot/compressed/Makefile |
901 | cflags-$(CONFIG_X86_32) := -march=i386 | |
902 | cflags-$(CONFIG_X86_64) := -mcmodel=small | |
a0f97e06 | 903 | KBUILD_CFLAGS += $(cflags-y) |
1da177e4 LT |
904 | |
905 | Many arch Makefiles dynamically run the target C compiler to | |
cd238eff | 906 | probe supported options:: |
1da177e4 | 907 | |
25eb650a | 908 | #arch/x86/Makefile |
1da177e4 LT |
909 | |
910 | ... | |
911 | cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ | |
912 | -march=pentium2,-march=i686) | |
913 | ... | |
914 | # Disable unit-at-a-time mode ... | |
a0f97e06 | 915 | KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time) |
1da177e4 LT |
916 | ... |
917 | ||
918 | ||
a07f6033 | 919 | The first example utilises the trick that a config option expands |
1da177e4 LT |
920 | to 'y' when selected. |
921 | ||
cd238eff | 922 | KBUILD_AFLAGS_KERNEL |
5ef87263 | 923 | Assembler options specific for built-in |
1da177e4 | 924 | |
80c00ba9 | 925 | $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile |
1da177e4 LT |
926 | resident kernel code. |
927 | ||
cd238eff | 928 | KBUILD_AFLAGS_MODULE |
5ef87263 | 929 | Assembler options specific for modules |
1da177e4 | 930 | |
39fed701 | 931 | $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that |
5ef87263 | 932 | are used for assembler. |
cd238eff | 933 | |
6588169d | 934 | From commandline AFLAGS_MODULE shall be used (see kbuild.txt). |
1da177e4 | 935 | |
cd238eff MCC |
936 | KBUILD_CFLAGS_KERNEL |
937 | $(CC) options specific for built-in | |
80c00ba9 SR |
938 | |
939 | $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile | |
940 | resident kernel code. | |
941 | ||
cd238eff MCC |
942 | KBUILD_CFLAGS_MODULE |
943 | Options for $(CC) when building modules | |
6588169d | 944 | |
39fed701 | 945 | $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that |
6588169d SR |
946 | are used for $(CC). |
947 | From commandline CFLAGS_MODULE shall be used (see kbuild.txt). | |
948 | ||
cd238eff MCC |
949 | KBUILD_LDFLAGS_MODULE |
950 | Options for $(LD) when linking modules | |
6588169d | 951 | |
39fed701 | 952 | $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options |
6588169d | 953 | used when linking modules. This is often a linker script. |
cd238eff | 954 | |
6588169d | 955 | From commandline LDFLAGS_MODULE shall be used (see kbuild.txt). |
39e6e9cf | 956 | |
888f0c34 MY |
957 | KBUILD_LDS |
958 | ||
959 | The linker script with full path. Assigned by the top-level Makefile. | |
960 | ||
10df0638 MY |
961 | KBUILD_LDS_MODULE |
962 | ||
963 | The module linker script with full path. Assigned by the top-level | |
964 | Makefile and additionally by the arch Makefile. | |
965 | ||
888f0c34 MY |
966 | KBUILD_VMLINUX_OBJS |
967 | ||
968 | All object files for vmlinux. They are linked to vmlinux in the same | |
969 | order as listed in KBUILD_VMLINUX_OBJS. | |
970 | ||
971 | KBUILD_VMLINUX_LIBS | |
972 | ||
973 | All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and | |
974 | KBUILD_VMLINUX_LIBS together specify all the object files used to | |
975 | link vmlinux. | |
61754c18 | 976 | |
cd238eff MCC |
977 | 6.2 Add prerequisites to archheaders |
978 | ------------------------------------ | |
052ad274 PA |
979 | |
980 | The archheaders: rule is used to generate header files that | |
f3c8d4c7 | 981 | may be installed into user space by "make header_install". |
052ad274 PA |
982 | |
983 | It is run before "make archprepare" when run on the | |
984 | architecture itself. | |
985 | ||
986 | ||
cd238eff MCC |
987 | 6.3 Add prerequisites to archprepare |
988 | ------------------------------------ | |
1da177e4 | 989 | |
a07f6033 | 990 | The archprepare: rule is used to list prerequisites that need to be |
1da177e4 | 991 | built before starting to descend down in the subdirectories. |
a07f6033 | 992 | This is usually used for header files containing assembler constants. |
1da177e4 | 993 | |
cd238eff MCC |
994 | Example:: |
995 | ||
5bb78269 SR |
996 | #arch/arm/Makefile |
997 | archprepare: maketools | |
1da177e4 | 998 | |
a07f6033 | 999 | In this example, the file target maketools will be processed |
5bb78269 | 1000 | before descending down in the subdirectories. |
1da177e4 LT |
1001 | See also chapter XXX-TODO that describe how kbuild supports |
1002 | generating offset header files. | |
1003 | ||
1004 | ||
cd238eff MCC |
1005 | 6.4 List directories to visit when descending |
1006 | --------------------------------------------- | |
1da177e4 LT |
1007 | |
1008 | An arch Makefile cooperates with the top Makefile to define variables | |
1009 | which specify how to build the vmlinux file. Note that there is no | |
1010 | corresponding arch-specific section for modules; the module-building | |
1011 | machinery is all architecture-independent. | |
1012 | ||
39e6e9cf | 1013 | |
cd238eff MCC |
1014 | head-y, init-y, core-y, libs-y, drivers-y, net-y |
1015 | $(head-y) lists objects to be linked first in vmlinux. | |
1016 | ||
1017 | $(libs-y) lists directories where a lib.a archive can be located. | |
1018 | ||
1019 | The rest list directories where a built-in.a object file can be | |
1020 | located. | |
1da177e4 | 1021 | |
cd238eff | 1022 | $(init-y) objects will be located after $(head-y). |
1da177e4 | 1023 | |
cd238eff | 1024 | Then the rest follows in this order: |
1da177e4 | 1025 | |
cd238eff MCC |
1026 | $(core-y), $(libs-y), $(drivers-y) and $(net-y). |
1027 | ||
1028 | The top level Makefile defines values for all generic directories, | |
1029 | and arch/$(ARCH)/Makefile only adds architecture-specific | |
1030 | directories. | |
1031 | ||
1032 | Example:: | |
1da177e4 | 1033 | |
1da177e4 LT |
1034 | #arch/sparc64/Makefile |
1035 | core-y += arch/sparc64/kernel/ | |
1036 | libs-y += arch/sparc64/prom/ arch/sparc64/lib/ | |
1037 | drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ | |
1038 | ||
1039 | ||
cd238eff MCC |
1040 | 6.5 Architecture-specific boot images |
1041 | ------------------------------------- | |
1da177e4 LT |
1042 | |
1043 | An arch Makefile specifies goals that take the vmlinux file, compress | |
1044 | it, wrap it in bootstrapping code, and copy the resulting files | |
1045 | somewhere. This includes various kinds of installation commands. | |
1046 | The actual goals are not standardized across architectures. | |
1047 | ||
1048 | It is common to locate any additional processing in a boot/ | |
1049 | directory below arch/$(ARCH)/. | |
1050 | ||
1051 | Kbuild does not provide any smart way to support building a | |
1052 | target specified in boot/. Therefore arch/$(ARCH)/Makefile shall | |
1053 | call make manually to build a target in boot/. | |
1054 | ||
1055 | The recommended approach is to include shortcuts in | |
1056 | arch/$(ARCH)/Makefile, and use the full path when calling down | |
1057 | into the arch/$(ARCH)/boot/Makefile. | |
1058 | ||
cd238eff MCC |
1059 | Example:: |
1060 | ||
25eb650a WG |
1061 | #arch/x86/Makefile |
1062 | boot := arch/x86/boot | |
1da177e4 LT |
1063 | bzImage: vmlinux |
1064 | $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ | |
1065 | ||
1066 | "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke | |
1067 | make in a subdirectory. | |
1068 | ||
5c811e59 | 1069 | There are no rules for naming architecture-specific targets, |
1da177e4 | 1070 | but executing "make help" will list all relevant targets. |
a07f6033 | 1071 | To support this, $(archhelp) must be defined. |
1da177e4 | 1072 | |
cd238eff MCC |
1073 | Example:: |
1074 | ||
25eb650a | 1075 | #arch/x86/Makefile |
1da177e4 LT |
1076 | define archhelp |
1077 | echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)' | |
39e6e9cf | 1078 | endif |
1da177e4 LT |
1079 | |
1080 | When make is executed without arguments, the first goal encountered | |
1081 | will be built. In the top level Makefile the first goal present | |
1082 | is all:. | |
a07f6033 JE |
1083 | An architecture shall always, per default, build a bootable image. |
1084 | In "make help", the default goal is highlighted with a '*'. | |
1da177e4 LT |
1085 | Add a new prerequisite to all: to select a default goal different |
1086 | from vmlinux. | |
1087 | ||
cd238eff MCC |
1088 | Example:: |
1089 | ||
25eb650a | 1090 | #arch/x86/Makefile |
39e6e9cf | 1091 | all: bzImage |
1da177e4 LT |
1092 | |
1093 | When "make" is executed without arguments, bzImage will be built. | |
1094 | ||
cd238eff MCC |
1095 | 6.6 Building non-kbuild targets |
1096 | ------------------------------- | |
1da177e4 LT |
1097 | |
1098 | extra-y | |
39fed701 | 1099 | extra-y specifies additional targets created in the current |
cd238eff | 1100 | directory, in addition to any targets specified by `obj-*`. |
1da177e4 LT |
1101 | |
1102 | Listing all targets in extra-y is required for two purposes: | |
cd238eff | 1103 | |
1da177e4 | 1104 | 1) Enable kbuild to check changes in command lines |
cd238eff | 1105 | |
1da177e4 | 1106 | - When $(call if_changed,xxx) is used |
cd238eff | 1107 | |
1da177e4 LT |
1108 | 2) kbuild knows what files to delete during "make clean" |
1109 | ||
cd238eff MCC |
1110 | Example:: |
1111 | ||
25eb650a | 1112 | #arch/x86/kernel/Makefile |
1da177e4 LT |
1113 | extra-y := head.o init_task.o |
1114 | ||
a07f6033 | 1115 | In this example, extra-y is used to list object files that |
f49821ee | 1116 | shall be built, but shall not be linked as part of built-in.a. |
1da177e4 | 1117 | |
cd238eff MCC |
1118 | 6.7 Commands useful for building a boot image |
1119 | --------------------------------------------- | |
1da177e4 | 1120 | |
cd238eff MCC |
1121 | Kbuild provides a few macros that are useful when building a |
1122 | boot image. | |
1da177e4 LT |
1123 | |
1124 | if_changed | |
1da177e4 LT |
1125 | if_changed is the infrastructure used for the following commands. |
1126 | ||
cd238eff MCC |
1127 | Usage:: |
1128 | ||
1da177e4 | 1129 | target: source(s) FORCE |
ef80f0a1 | 1130 | $(call if_changed,ld/objcopy/gzip/...) |
1da177e4 | 1131 | |
a07f6033 | 1132 | When the rule is evaluated, it is checked to see if any files |
5c811e59 | 1133 | need an update, or the command line has changed since the last |
1da177e4 LT |
1134 | invocation. The latter will force a rebuild if any options |
1135 | to the executable have changed. | |
1136 | Any target that utilises if_changed must be listed in $(targets), | |
1137 | otherwise the command line check will fail, and the target will | |
1138 | always be built. | |
1139 | Assignments to $(targets) are without $(obj)/ prefix. | |
1140 | if_changed may be used in conjunction with custom commands as | |
052ad274 | 1141 | defined in 6.8 "Custom kbuild commands". |
49490571 | 1142 | |
1da177e4 | 1143 | Note: It is a typical mistake to forget the FORCE prerequisite. |
49490571 PBG |
1144 | Another common pitfall is that whitespace is sometimes |
1145 | significant; for instance, the below will fail (note the extra space | |
cd238eff MCC |
1146 | after the comma):: |
1147 | ||
49490571 | 1148 | target: source(s) FORCE |
1da177e4 | 1149 | |
cd238eff MCC |
1150 | **WRONG!** $(call if_changed, ld/objcopy/gzip/...) |
1151 | ||
1152 | Note: | |
1153 | if_changed should not be used more than once per target. | |
bb81955f | 1154 | It stores the executed command in a corresponding .cmd |
cd238eff | 1155 | |
bb81955f DG |
1156 | file and multiple calls would result in overwrites and |
1157 | unwanted results when the target is up to date and only the | |
1158 | tests on changed commands trigger execution of commands. | |
1159 | ||
1da177e4 | 1160 | ld |
a07f6033 | 1161 | Link target. Often, LDFLAGS_$@ is used to set specific options to ld. |
39e6e9cf | 1162 | |
cd238eff MCC |
1163 | Example:: |
1164 | ||
25eb650a | 1165 | #arch/x86/boot/Makefile |
1da177e4 LT |
1166 | LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary |
1167 | LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext | |
1168 | ||
1169 | targets += setup setup.o bootsect bootsect.o | |
1170 | $(obj)/setup $(obj)/bootsect: %: %.o FORCE | |
1171 | $(call if_changed,ld) | |
1172 | ||
a07f6033 JE |
1173 | In this example, there are two possible targets, requiring different |
1174 | options to the linker. The linker options are specified using the | |
1da177e4 | 1175 | LDFLAGS_$@ syntax - one for each potential target. |
5d3f083d | 1176 | $(targets) are assigned all potential targets, by which kbuild knows |
1da177e4 | 1177 | the targets and will: |
cd238eff | 1178 | |
1da177e4 LT |
1179 | 1) check for commandline changes |
1180 | 2) delete target during make clean | |
1181 | ||
1182 | The ": %: %.o" part of the prerequisite is a shorthand that | |
39fed701 | 1183 | frees us from listing the setup.o and bootsect.o files. |
cd238eff MCC |
1184 | |
1185 | Note: | |
1186 | It is a common mistake to forget the "targets :=" assignment, | |
1da177e4 LT |
1187 | resulting in the target file being recompiled for no |
1188 | obvious reason. | |
1189 | ||
d87e47e1 C |
1190 | objcopy |
1191 | Copy binary. Uses OBJCOPYFLAGS usually specified in | |
1192 | arch/$(ARCH)/Makefile. | |
1193 | OBJCOPYFLAGS_$@ may be used to set additional options. | |
1194 | ||
1195 | gzip | |
1196 | Compress target. Use maximum compression to compress target. | |
1197 | ||
cd238eff MCC |
1198 | Example:: |
1199 | ||
d87e47e1 C |
1200 | #arch/x86/boot/compressed/Makefile |
1201 | $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE | |
1202 | $(call if_changed,gzip) | |
1203 | ||
aab94339 | 1204 | dtc |
c1410562 | 1205 | Create flattened device tree blob object suitable for linking |
aab94339 DB |
1206 | into vmlinux. Device tree blobs linked into vmlinux are placed |
1207 | in an init section in the image. Platform code *must* copy the | |
1208 | blob to non-init memory prior to calling unflatten_device_tree(). | |
1209 | ||
cd238eff MCC |
1210 | To use this command, simply add `*.dtb` into obj-y or targets, or make |
1211 | some other target depend on `%.dtb` | |
aab94339 | 1212 | |
cd238eff | 1213 | A central rule exists to create `$(obj)/%.dtb` from `$(src)/%.dts`; |
90b335fb | 1214 | architecture Makefiles do no need to explicitly write out that rule. |
aab94339 | 1215 | |
cd238eff MCC |
1216 | Example:: |
1217 | ||
90b335fb | 1218 | targets += $(dtb-y) |
90b335fb | 1219 | DTC_FLAGS ?= -p 1024 |
1da177e4 | 1220 | |
cd238eff MCC |
1221 | 6.8 Custom kbuild commands |
1222 | -------------------------- | |
1da177e4 | 1223 | |
a07f6033 | 1224 | When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand |
1da177e4 LT |
1225 | of a command is normally displayed. |
1226 | To enable this behaviour for custom commands kbuild requires | |
cd238eff MCC |
1227 | two variables to be set:: |
1228 | ||
1229 | quiet_cmd_<command> - what shall be echoed | |
1230 | cmd_<command> - the command to execute | |
1231 | ||
1232 | Example:: | |
1da177e4 | 1233 | |
1da177e4 LT |
1234 | # |
1235 | quiet_cmd_image = BUILD $@ | |
1236 | cmd_image = $(obj)/tools/build $(BUILDFLAGS) \ | |
1237 | $(obj)/vmlinux.bin > $@ | |
1238 | ||
1239 | targets += bzImage | |
1240 | $(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE | |
1241 | $(call if_changed,image) | |
1242 | @echo 'Kernel: $@ is ready' | |
1243 | ||
cd238eff | 1244 | When updating the $(obj)/bzImage target, the line: |
1da177e4 | 1245 | |
cd238eff | 1246 | BUILD arch/x86/boot/bzImage |
1da177e4 LT |
1247 | |
1248 | will be displayed with "make KBUILD_VERBOSE=0". | |
39e6e9cf | 1249 | |
1da177e4 | 1250 | |
052ad274 | 1251 | --- 6.9 Preprocessing linker scripts |
1da177e4 | 1252 | |
a07f6033 | 1253 | When the vmlinux image is built, the linker script |
1da177e4 LT |
1254 | arch/$(ARCH)/kernel/vmlinux.lds is used. |
1255 | The script is a preprocessed variant of the file vmlinux.lds.S | |
1256 | located in the same directory. | |
cd238eff MCC |
1257 | kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`. |
1258 | ||
1259 | Example:: | |
39e6e9cf | 1260 | |
25eb650a | 1261 | #arch/x86/kernel/Makefile |
1da177e4 | 1262 | always := vmlinux.lds |
39e6e9cf | 1263 | |
1da177e4 LT |
1264 | #Makefile |
1265 | export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH) | |
39e6e9cf BH |
1266 | |
1267 | The assignment to $(always) is used to tell kbuild to build the | |
a07f6033 JE |
1268 | target vmlinux.lds. |
1269 | The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the | |
1da177e4 | 1270 | specified options when building the target vmlinux.lds. |
39e6e9cf | 1271 | |
cd238eff MCC |
1272 | When building the `*.lds` target, kbuild uses the variables:: |
1273 | ||
1274 | KBUILD_CPPFLAGS : Set in top-level Makefile | |
1275 | cppflags-y : May be set in the kbuild makefile | |
1276 | CPPFLAGS_$(@F) : Target-specific flags. | |
1277 | Note that the full filename is used in this | |
1278 | assignment. | |
1da177e4 | 1279 | |
cd238eff | 1280 | The kbuild infrastructure for `*lds` files is used in several |
5c811e59 | 1281 | architecture-specific files. |
1da177e4 | 1282 | |
cd238eff MCC |
1283 | 6.10 Generic header files |
1284 | ------------------------- | |
d8ecc5cd SR |
1285 | |
1286 | The directory include/asm-generic contains the header files | |
1287 | that may be shared between individual architectures. | |
1288 | The recommended approach how to use a generic header file is | |
1289 | to list the file in the Kbuild file. | |
d87e47e1 | 1290 | See "7.2 generic-y" for further info on syntax etc. |
d8ecc5cd | 1291 | |
cd238eff MCC |
1292 | 6.11 Post-link pass |
1293 | ------------------- | |
fbe6e37d NP |
1294 | |
1295 | If the file arch/xxx/Makefile.postlink exists, this makefile | |
1296 | will be invoked for post-link objects (vmlinux and modules.ko) | |
1297 | for architectures to run post-link passes on. Must also handle | |
1298 | the clean target. | |
1299 | ||
1300 | This pass runs after kallsyms generation. If the architecture | |
1301 | needs to modify symbol locations, rather than manipulate the | |
1302 | kallsyms, it may be easier to add another postlink target for | |
1303 | .tmp_vmlinux? targets to be called from link-vmlinux.sh. | |
1304 | ||
1305 | For example, powerpc uses this to check relocation sanity of | |
1306 | the linked vmlinux file. | |
1307 | ||
cd238eff MCC |
1308 | 7 Kbuild syntax for exported headers |
1309 | ------------------------------------ | |
c7bb349e | 1310 | |
39fed701 | 1311 | The kernel includes a set of headers that is exported to userspace. |
c95940f2 | 1312 | Many headers can be exported as-is but other headers require a |
c7bb349e SR |
1313 | minimal pre-processing before they are ready for user-space. |
1314 | The pre-processing does: | |
cd238eff | 1315 | |
39fed701 | 1316 | - drop kernel-specific annotations |
c7bb349e | 1317 | - drop include of compiler.h |
cd238eff | 1318 | - drop all sections that are kernel internal (guarded by `ifdef __KERNEL__`) |
c7bb349e | 1319 | |
fcc8487d | 1320 | All headers under include/uapi/, include/generated/uapi/, |
61562f98 | 1321 | arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/ |
fcc8487d | 1322 | are exported. |
c7bb349e | 1323 | |
fcc8487d ND |
1324 | A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and |
1325 | arch/<arch>/include/asm/ to list asm files coming from asm-generic. | |
1326 | See subsequent chapter for the syntax of the Kbuild file. | |
c7bb349e | 1327 | |
cd238eff MCC |
1328 | 7.1 no-export-headers |
1329 | --------------------- | |
c7bb349e | 1330 | |
fcc8487d ND |
1331 | no-export-headers is essentially used by include/uapi/linux/Kbuild to |
1332 | avoid exporting specific headers (e.g. kvm.h) on architectures that do | |
1333 | not support it. It should be avoided as much as possible. | |
c7bb349e | 1334 | |
cd238eff MCC |
1335 | 7.2 generic-y |
1336 | ------------- | |
d8ecc5cd SR |
1337 | |
1338 | If an architecture uses a verbatim copy of a header from | |
1339 | include/asm-generic then this is listed in the file | |
1340 | arch/$(ARCH)/include/asm/Kbuild like this: | |
1341 | ||
cd238eff MCC |
1342 | Example:: |
1343 | ||
d8ecc5cd SR |
1344 | #arch/x86/include/asm/Kbuild |
1345 | generic-y += termios.h | |
1346 | generic-y += rtc.h | |
1347 | ||
1348 | During the prepare phase of the build a wrapper include | |
cd238eff | 1349 | file is generated in the directory:: |
d8ecc5cd SR |
1350 | |
1351 | arch/$(ARCH)/include/generated/asm | |
1352 | ||
1353 | When a header is exported where the architecture uses | |
1354 | the generic header a similar wrapper is generated as part | |
cd238eff | 1355 | of the set of exported headers in the directory:: |
d8ecc5cd SR |
1356 | |
1357 | usr/include/asm | |
1358 | ||
1359 | The generated wrapper will in both cases look like the following: | |
1360 | ||
cd238eff MCC |
1361 | Example: termios.h:: |
1362 | ||
d8ecc5cd | 1363 | #include <asm-generic/termios.h> |
c7bb349e | 1364 | |
cd238eff MCC |
1365 | 7.3 generated-y |
1366 | --------------- | |
54b880ca JH |
1367 | |
1368 | If an architecture generates other header files alongside generic-y | |
ae3f4151 | 1369 | wrappers, generated-y specifies them. |
54b880ca JH |
1370 | |
1371 | This prevents them being treated as stale asm-generic wrappers and | |
1372 | removed. | |
1373 | ||
cd238eff MCC |
1374 | Example:: |
1375 | ||
54b880ca JH |
1376 | #arch/x86/include/asm/Kbuild |
1377 | generated-y += syscalls_32.h | |
1378 | ||
cd238eff MCC |
1379 | 7.4 mandatory-y |
1380 | --------------- | |
fcc8487d | 1381 | |
037fc336 | 1382 | mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild |
91998731 MY |
1383 | to define the minimum set of ASM headers that all architectures must have. |
1384 | ||
1385 | This works like optional generic-y. If a mandatory header is missing | |
1386 | in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate | |
1387 | a wrapper of the asm-generic one. | |
fcc8487d ND |
1388 | |
1389 | The convention is to list one subdir per line and | |
1390 | preferably in alphabetic order. | |
1391 | ||
cd238eff MCC |
1392 | 8 Kbuild Variables |
1393 | ================== | |
1da177e4 LT |
1394 | |
1395 | The top Makefile exports the following variables: | |
1396 | ||
1397 | VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION | |
1da177e4 LT |
1398 | These variables define the current kernel version. A few arch |
1399 | Makefiles actually use these values directly; they should use | |
1400 | $(KERNELRELEASE) instead. | |
1401 | ||
1402 | $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic | |
1403 | three-part version number, such as "2", "4", and "0". These three | |
1404 | values are always numeric. | |
1405 | ||
1406 | $(EXTRAVERSION) defines an even tinier sublevel for pre-patches | |
1407 | or additional patches. It is usually some non-numeric string | |
1408 | such as "-pre4", and is often blank. | |
1409 | ||
1410 | KERNELRELEASE | |
1da177e4 LT |
1411 | $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable |
1412 | for constructing installation directory names or showing in | |
1413 | version strings. Some arch Makefiles use it for this purpose. | |
1414 | ||
1415 | ARCH | |
1da177e4 LT |
1416 | This variable defines the target architecture, such as "i386", |
1417 | "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to | |
1418 | determine which files to compile. | |
1419 | ||
1420 | By default, the top Makefile sets $(ARCH) to be the same as the | |
1421 | host system architecture. For a cross build, a user may | |
cd238eff | 1422 | override the value of $(ARCH) on the command line:: |
1da177e4 LT |
1423 | |
1424 | make ARCH=m68k ... | |
1425 | ||
1426 | ||
1427 | INSTALL_PATH | |
1da177e4 LT |
1428 | This variable defines a place for the arch Makefiles to install |
1429 | the resident kernel image and System.map file. | |
5c811e59 | 1430 | Use this for architecture-specific install targets. |
1da177e4 LT |
1431 | |
1432 | INSTALL_MOD_PATH, MODLIB | |
1da177e4 LT |
1433 | $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module |
1434 | installation. This variable is not defined in the Makefile but | |
1435 | may be passed in by the user if desired. | |
1436 | ||
1437 | $(MODLIB) specifies the directory for module installation. | |
1438 | The top Makefile defines $(MODLIB) to | |
1439 | $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may | |
1440 | override this value on the command line if desired. | |
1441 | ||
ac031f26 | 1442 | INSTALL_MOD_STRIP |
39fed701 | 1443 | If this variable is specified, it will cause modules to be stripped |
ac031f26 | 1444 | after they are installed. If INSTALL_MOD_STRIP is '1', then the |
39fed701 | 1445 | default option --strip-debug will be used. Otherwise, the |
177b241d GE |
1446 | INSTALL_MOD_STRIP value will be used as the option(s) to the strip |
1447 | command. | |
ac031f26 TT |
1448 | |
1449 | ||
cd238eff MCC |
1450 | 9 Makefile language |
1451 | =================== | |
1da177e4 | 1452 | |
a07f6033 | 1453 | The kernel Makefiles are designed to be run with GNU Make. The Makefiles |
1da177e4 LT |
1454 | use only the documented features of GNU Make, but they do use many |
1455 | GNU extensions. | |
1456 | ||
1457 | GNU Make supports elementary list-processing functions. The kernel | |
1458 | Makefiles use a novel style of list building and manipulation with few | |
1459 | "if" statements. | |
1460 | ||
1461 | GNU Make has two assignment operators, ":=" and "=". ":=" performs | |
1462 | immediate evaluation of the right-hand side and stores an actual string | |
1463 | into the left-hand side. "=" is like a formula definition; it stores the | |
1464 | right-hand side in an unevaluated form and then evaluates this form each | |
1465 | time the left-hand side is used. | |
1466 | ||
1467 | There are some cases where "=" is appropriate. Usually, though, ":=" | |
1468 | is the right choice. | |
1469 | ||
cd238eff MCC |
1470 | 10 Credits |
1471 | ========== | |
1da177e4 | 1472 | |
cd238eff MCC |
1473 | - Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> |
1474 | - Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de> | |
1475 | - Updates by Sam Ravnborg <sam@ravnborg.org> | |
1476 | - Language QA by Jan Engelhardt <jengelh@gmx.de> | |
1da177e4 | 1477 | |
cd238eff MCC |
1478 | 11 TODO |
1479 | ======= | |
1da177e4 | 1480 | |
a07f6033 | 1481 | - Describe how kbuild supports shipped files with _shipped. |
1da177e4 LT |
1482 | - Generating offset header files. |
1483 | - Add more variables to section 7? |