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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 $(LD) support functions |
1da177e4 LT |
24 | |
25 | === 4 Host Program support | |
26 | --- 4.1 Simple Host Program | |
27 | --- 4.2 Composite Host Programs | |
62e22107 MY |
28 | --- 4.3 Using C++ for host programs |
29 | --- 4.4 Controlling compiler options for host programs | |
30 | --- 4.5 When host programs are actually built | |
1da177e4 LT |
31 | |
32 | === 5 Kbuild clean infrastructure | |
33 | ||
34 | === 6 Architecture Makefiles | |
35 | --- 6.1 Set variables to tweak the build to the architecture | |
052ad274 PA |
36 | --- 6.2 Add prerequisites to archheaders: |
37 | --- 6.3 Add prerequisites to archprepare: | |
38 | --- 6.4 List directories to visit when descending | |
39 | --- 6.5 Architecture-specific boot images | |
40 | --- 6.6 Building non-kbuild targets | |
41 | --- 6.7 Commands useful for building a boot image | |
42 | --- 6.8 Custom kbuild commands | |
43 | --- 6.9 Preprocessing linker scripts | |
44 | --- 6.10 Generic header files | |
fbe6e37d | 45 | --- 6.11 Post-link pass |
1da177e4 | 46 | |
c7bb349e | 47 | === 7 Kbuild syntax for exported headers |
fcc8487d | 48 | --- 7.1 no-export-headers |
ae3f4151 MY |
49 | --- 7.2 generic-y |
50 | --- 7.3 generated-y | |
51 | --- 7.4 mandatory-y | |
c7bb349e SR |
52 | |
53 | === 8 Kbuild Variables | |
54 | === 9 Makefile language | |
55 | === 10 Credits | |
56 | === 11 TODO | |
1da177e4 | 57 | |
cd238eff MCC |
58 | 1 Overview |
59 | ========== | |
1da177e4 | 60 | |
cd238eff | 61 | The Makefiles have five parts:: |
1da177e4 LT |
62 | |
63 | Makefile the top Makefile. | |
64 | .config the kernel configuration file. | |
65 | arch/$(ARCH)/Makefile the arch Makefile. | |
66 | scripts/Makefile.* common rules etc. for all kbuild Makefiles. | |
67 | kbuild Makefiles there are about 500 of these. | |
68 | ||
69 | The top Makefile reads the .config file, which comes from the kernel | |
70 | configuration process. | |
71 | ||
72 | The top Makefile is responsible for building two major products: vmlinux | |
73 | (the resident kernel image) and modules (any module files). | |
74 | It builds these goals by recursively descending into the subdirectories of | |
75 | the kernel source tree. | |
76 | The list of subdirectories which are visited depends upon the kernel | |
77 | configuration. The top Makefile textually includes an arch Makefile | |
78 | with the name arch/$(ARCH)/Makefile. The arch Makefile supplies | |
79 | architecture-specific information to the top Makefile. | |
80 | ||
81 | Each subdirectory has a kbuild Makefile which carries out the commands | |
82 | passed down from above. The kbuild Makefile uses information from the | |
39e6e9cf | 83 | .config file to construct various file lists used by kbuild to build |
1da177e4 LT |
84 | any built-in or modular targets. |
85 | ||
86 | scripts/Makefile.* contains all the definitions/rules etc. that | |
87 | are used to build the kernel based on the kbuild makefiles. | |
88 | ||
89 | ||
cd238eff MCC |
90 | 2 Who does what |
91 | =============== | |
1da177e4 LT |
92 | |
93 | People have four different relationships with the kernel Makefiles. | |
94 | ||
95 | *Users* are people who build kernels. These people type commands such as | |
96 | "make menuconfig" or "make". They usually do not read or edit | |
97 | any kernel Makefiles (or any other source files). | |
98 | ||
99 | *Normal developers* are people who work on features such as device | |
100 | drivers, file systems, and network protocols. These people need to | |
a07f6033 | 101 | maintain the kbuild Makefiles for the subsystem they are |
1da177e4 LT |
102 | working on. In order to do this effectively, they need some overall |
103 | knowledge about the kernel Makefiles, plus detailed knowledge about the | |
104 | public interface for kbuild. | |
105 | ||
106 | *Arch developers* are people who work on an entire architecture, such | |
107 | as sparc or ia64. Arch developers need to know about the arch Makefile | |
108 | as well as kbuild Makefiles. | |
109 | ||
110 | *Kbuild developers* are people who work on the kernel build system itself. | |
111 | These people need to know about all aspects of the kernel Makefiles. | |
112 | ||
113 | This document is aimed towards normal developers and arch developers. | |
114 | ||
115 | ||
cd238eff MCC |
116 | 3 The kbuild files |
117 | ================== | |
1da177e4 LT |
118 | |
119 | Most Makefiles within the kernel are kbuild Makefiles that use the | |
a07f6033 | 120 | kbuild infrastructure. This chapter introduces the syntax used in the |
1da177e4 | 121 | kbuild makefiles. |
172c3ae3 | 122 | The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can |
a07f6033 | 123 | be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild' |
172c3ae3 | 124 | file will be used. |
1da177e4 LT |
125 | |
126 | Section 3.1 "Goal definitions" is a quick intro, further chapters provide | |
127 | more details, with real examples. | |
128 | ||
cd238eff MCC |
129 | 3.1 Goal definitions |
130 | -------------------- | |
1da177e4 LT |
131 | |
132 | Goal definitions are the main part (heart) of the kbuild Makefile. | |
133 | These lines define the files to be built, any special compilation | |
134 | options, and any subdirectories to be entered recursively. | |
135 | ||
136 | The most simple kbuild makefile contains one line: | |
137 | ||
cd238eff MCC |
138 | Example:: |
139 | ||
1da177e4 LT |
140 | obj-y += foo.o |
141 | ||
5c811e59 | 142 | This tells kbuild that there is one object in that directory, named |
1da177e4 LT |
143 | foo.o. foo.o will be built from foo.c or foo.S. |
144 | ||
145 | If foo.o shall be built as a module, the variable obj-m is used. | |
146 | Therefore the following pattern is often used: | |
147 | ||
cd238eff MCC |
148 | Example:: |
149 | ||
1da177e4 LT |
150 | obj-$(CONFIG_FOO) += foo.o |
151 | ||
152 | $(CONFIG_FOO) evaluates to either y (for built-in) or m (for module). | |
153 | If CONFIG_FOO is neither y nor m, then the file will not be compiled | |
154 | nor linked. | |
155 | ||
cd238eff MCC |
156 | 3.2 Built-in object goals - obj-y |
157 | --------------------------------- | |
1da177e4 LT |
158 | |
159 | The kbuild Makefile specifies object files for vmlinux | |
a07f6033 | 160 | in the $(obj-y) lists. These lists depend on the kernel |
1da177e4 LT |
161 | configuration. |
162 | ||
163 | Kbuild compiles all the $(obj-y) files. It then calls | |
f49821ee | 164 | "$(AR) rcSTP" to merge these files into one built-in.a file. |
dee94953 MY |
165 | This is a thin archive without a symbol table. It will be later |
166 | linked into vmlinux by scripts/link-vmlinux.sh | |
1da177e4 LT |
167 | |
168 | The order of files in $(obj-y) is significant. Duplicates in | |
169 | the lists are allowed: the first instance will be linked into | |
f49821ee | 170 | built-in.a and succeeding instances will be ignored. |
1da177e4 LT |
171 | |
172 | Link order is significant, because certain functions | |
173 | (module_init() / __initcall) will be called during boot in the | |
174 | order they appear. So keep in mind that changing the link | |
a07f6033 JE |
175 | order may e.g. change the order in which your SCSI |
176 | controllers are detected, and thus your disks are renumbered. | |
1da177e4 | 177 | |
cd238eff MCC |
178 | Example:: |
179 | ||
1da177e4 LT |
180 | #drivers/isdn/i4l/Makefile |
181 | # Makefile for the kernel ISDN subsystem and device drivers. | |
182 | # Each configuration option enables a list of files. | |
2f5a2f81 | 183 | obj-$(CONFIG_ISDN_I4L) += isdn.o |
1da177e4 LT |
184 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o |
185 | ||
cd238eff MCC |
186 | 3.3 Loadable module goals - obj-m |
187 | --------------------------------- | |
1da177e4 | 188 | |
39fed701 | 189 | $(obj-m) specifies object files which are built as loadable |
1da177e4 LT |
190 | kernel modules. |
191 | ||
192 | A module may be built from one source file or several source | |
193 | files. In the case of one source file, the kbuild makefile | |
194 | simply adds the file to $(obj-m). | |
195 | ||
cd238eff MCC |
196 | Example:: |
197 | ||
1da177e4 LT |
198 | #drivers/isdn/i4l/Makefile |
199 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o | |
200 | ||
201 | Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm' | |
202 | ||
203 | If a kernel module is built from several source files, you specify | |
4f827280 MM |
204 | that you want to build a module in the same way as above; however, |
205 | kbuild needs to know which object files you want to build your | |
206 | module from, so you have to tell it by setting a $(<module_name>-y) | |
207 | variable. | |
1da177e4 | 208 | |
cd238eff MCC |
209 | Example:: |
210 | ||
1da177e4 | 211 | #drivers/isdn/i4l/Makefile |
4f827280 MM |
212 | obj-$(CONFIG_ISDN_I4L) += isdn.o |
213 | isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o | |
1da177e4 LT |
214 | |
215 | In this example, the module name will be isdn.o. Kbuild will | |
4f827280 | 216 | compile the objects listed in $(isdn-y) and then run |
1da177e4 LT |
217 | "$(LD) -r" on the list of these files to generate isdn.o. |
218 | ||
4f827280 | 219 | Due to kbuild recognizing $(<module_name>-y) for composite objects, |
cd238eff | 220 | you can use the value of a `CONFIG_` symbol to optionally include an |
4f827280 | 221 | object file as part of a composite object. |
1da177e4 | 222 | |
cd238eff MCC |
223 | Example:: |
224 | ||
1da177e4 | 225 | #fs/ext2/Makefile |
4f827280 MM |
226 | obj-$(CONFIG_EXT2_FS) += ext2.o |
227 | ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \ | |
228 | namei.o super.o symlink.o | |
229 | ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \ | |
230 | xattr_trusted.o | |
231 | ||
232 | In this example, xattr.o, xattr_user.o and xattr_trusted.o are only | |
233 | part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR) | |
234 | evaluates to 'y'. | |
1da177e4 LT |
235 | |
236 | Note: Of course, when you are building objects into the kernel, | |
237 | the syntax above will also work. So, if you have CONFIG_EXT2_FS=y, | |
238 | kbuild will build an ext2.o file for you out of the individual | |
f49821ee | 239 | parts and then link this into built-in.a, as you would expect. |
1da177e4 | 240 | |
cd238eff MCC |
241 | 3.4 Objects which export symbols |
242 | -------------------------------- | |
1da177e4 LT |
243 | |
244 | No special notation is required in the makefiles for | |
245 | modules exporting symbols. | |
246 | ||
cd238eff MCC |
247 | 3.5 Library file goals - lib-y |
248 | ------------------------------ | |
1da177e4 | 249 | |
a07f6033 | 250 | Objects listed with obj-* are used for modules, or |
f49821ee | 251 | combined in a built-in.a for that specific directory. |
1da177e4 LT |
252 | There is also the possibility to list objects that will |
253 | be included in a library, lib.a. | |
254 | All objects listed with lib-y are combined in a single | |
255 | library for that directory. | |
5d3f083d ML |
256 | Objects that are listed in obj-y and additionally listed in |
257 | lib-y will not be included in the library, since they will | |
258 | be accessible anyway. | |
a07f6033 | 259 | For consistency, objects listed in lib-m will be included in lib.a. |
1da177e4 LT |
260 | |
261 | Note that the same kbuild makefile may list files to be built-in | |
262 | and to be part of a library. Therefore the same directory | |
f49821ee | 263 | may contain both a built-in.a and a lib.a file. |
1da177e4 | 264 | |
cd238eff MCC |
265 | Example:: |
266 | ||
2f5a2f81 MM |
267 | #arch/x86/lib/Makefile |
268 | lib-y := delay.o | |
1da177e4 | 269 | |
2f5a2f81 MM |
270 | This will create a library lib.a based on delay.o. For kbuild to |
271 | actually recognize that there is a lib.a being built, the directory | |
272 | shall be listed in libs-y. | |
cd238eff | 273 | |
052ad274 | 274 | See also "6.4 List directories to visit when descending". |
39e6e9cf | 275 | |
cd238eff | 276 | Use of lib-y is normally restricted to `lib/` and `arch/*/lib`. |
1da177e4 | 277 | |
cd238eff MCC |
278 | 3.6 Descending down in directories |
279 | ---------------------------------- | |
1da177e4 LT |
280 | |
281 | A Makefile is only responsible for building objects in its own | |
282 | directory. Files in subdirectories should be taken care of by | |
283 | Makefiles in these subdirs. The build system will automatically | |
284 | invoke make recursively in subdirectories, provided you let it know of | |
285 | them. | |
286 | ||
a07f6033 | 287 | To do so, obj-y and obj-m are used. |
1da177e4 LT |
288 | ext2 lives in a separate directory, and the Makefile present in fs/ |
289 | tells kbuild to descend down using the following assignment. | |
290 | ||
cd238eff MCC |
291 | Example:: |
292 | ||
1da177e4 LT |
293 | #fs/Makefile |
294 | obj-$(CONFIG_EXT2_FS) += ext2/ | |
295 | ||
296 | If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular) | |
297 | the corresponding obj- variable will be set, and kbuild will descend | |
298 | down in the ext2 directory. | |
28f94a44 MY |
299 | |
300 | Kbuild uses this information not only to decide that it needs to visit | |
301 | the directory, but also to decide whether or not to link objects from | |
302 | the directory into vmlinux. | |
303 | ||
304 | When Kbuild descends into the directory with 'y', all built-in objects | |
305 | from that directory are combined into the built-in.a, which will be | |
306 | eventually linked into vmlinux. | |
307 | ||
308 | When Kbuild descends into the directory with 'm', in contrast, nothing | |
309 | from that directory will be linked into vmlinux. If the Makefile in | |
310 | that directory specifies obj-y, those objects will be left orphan. | |
311 | It is very likely a bug of the Makefile or of dependencies in Kconfig. | |
1da177e4 | 312 | |
cd238eff | 313 | It is good practice to use a `CONFIG_` variable when assigning directory |
1da177e4 | 314 | names. This allows kbuild to totally skip the directory if the |
cd238eff | 315 | corresponding `CONFIG_` option is neither 'y' nor 'm'. |
1da177e4 | 316 | |
cd238eff MCC |
317 | 3.7 Compilation flags |
318 | --------------------- | |
1da177e4 | 319 | |
f77bf014 | 320 | ccflags-y, asflags-y and ldflags-y |
c95940f2 NK |
321 | These three flags apply only to the kbuild makefile in which they |
322 | are assigned. They are used for all the normal cc, as and ld | |
323 | invocations happening during a recursive build. | |
f77bf014 | 324 | Note: Flags with the same behaviour were previously named: |
c95940f2 NK |
325 | EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS. |
326 | They are still supported but their usage is deprecated. | |
1da177e4 | 327 | |
eb07e1b4 | 328 | ccflags-y specifies options for compiling with $(CC). |
1da177e4 | 329 | |
cd238eff MCC |
330 | Example:: |
331 | ||
3d91a353 SD |
332 | # drivers/acpi/acpica/Makefile |
333 | ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA | |
334 | ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT | |
1da177e4 LT |
335 | |
336 | This variable is necessary because the top Makefile owns the | |
a0f97e06 | 337 | variable $(KBUILD_CFLAGS) and uses it for compilation flags for the |
1da177e4 LT |
338 | entire tree. |
339 | ||
5ef87263 | 340 | asflags-y specifies assembler options. |
1da177e4 | 341 | |
cd238eff MCC |
342 | Example:: |
343 | ||
eb07e1b4 MM |
344 | #arch/sparc/kernel/Makefile |
345 | asflags-y := -ansi | |
1da177e4 | 346 | |
eb07e1b4 | 347 | ldflags-y specifies options for linking with $(LD). |
1da177e4 | 348 | |
cd238eff MCC |
349 | Example:: |
350 | ||
eb07e1b4 MM |
351 | #arch/cris/boot/compressed/Makefile |
352 | ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds | |
1da177e4 | 353 | |
720097d8 | 354 | subdir-ccflags-y, subdir-asflags-y |
eb07e1b4 | 355 | The two flags listed above are similar to ccflags-y and asflags-y. |
c95940f2 NK |
356 | The difference is that the subdir- variants have effect for the kbuild |
357 | file where they are present and all subdirectories. | |
358 | Options specified using subdir-* are added to the commandline before | |
359 | the options specified using the non-subdir variants. | |
720097d8 | 360 | |
cd238eff MCC |
361 | Example:: |
362 | ||
720097d8 SR |
363 | subdir-ccflags-y := -Werror |
364 | ||
1da177e4 | 365 | CFLAGS_$@, AFLAGS_$@ |
1da177e4 LT |
366 | CFLAGS_$@ and AFLAGS_$@ only apply to commands in current |
367 | kbuild makefile. | |
368 | ||
369 | $(CFLAGS_$@) specifies per-file options for $(CC). The $@ | |
370 | part has a literal value which specifies the file that it is for. | |
371 | ||
cd238eff MCC |
372 | Example:: |
373 | ||
1da177e4 LT |
374 | # drivers/scsi/Makefile |
375 | CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF | |
376 | CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \ | |
377 | -DGDTH_STATISTICS | |
1da177e4 | 378 | |
eb07e1b4 | 379 | These two lines specify compilation flags for aha152x.o and gdth.o. |
1da177e4 LT |
380 | |
381 | $(AFLAGS_$@) is a similar feature for source files in assembly | |
382 | languages. | |
383 | ||
cd238eff MCC |
384 | Example:: |
385 | ||
1da177e4 | 386 | # arch/arm/kernel/Makefile |
eb07e1b4 MM |
387 | AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) |
388 | AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312 | |
389 | AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt | |
390 | ||
1da177e4 | 391 | |
cd238eff MCC |
392 | 3.9 Dependency tracking |
393 | ----------------------- | |
1da177e4 LT |
394 | |
395 | Kbuild tracks dependencies on the following: | |
16886949 | 396 | |
cd238eff MCC |
397 | 1) All prerequisite files (both `*.c` and `*.h`) |
398 | 2) `CONFIG_` options used in all prerequisite files | |
1da177e4 LT |
399 | 3) Command-line used to compile target |
400 | ||
401 | Thus, if you change an option to $(CC) all affected files will | |
402 | be re-compiled. | |
403 | ||
cd238eff MCC |
404 | 3.10 Special Rules |
405 | ------------------ | |
1da177e4 LT |
406 | |
407 | Special rules are used when the kbuild infrastructure does | |
408 | not provide the required support. A typical example is | |
409 | header files generated during the build process. | |
5c811e59 | 410 | Another example are the architecture-specific Makefiles which |
a07f6033 | 411 | need special rules to prepare boot images etc. |
1da177e4 LT |
412 | |
413 | Special rules are written as normal Make rules. | |
414 | Kbuild is not executing in the directory where the Makefile is | |
415 | located, so all special rules shall provide a relative | |
416 | path to prerequisite files and target files. | |
417 | ||
418 | Two variables are used when defining special rules: | |
419 | ||
cd238eff MCC |
420 | $(src) |
421 | $(src) is a relative path which points to the directory | |
422 | where the Makefile is located. Always use $(src) when | |
423 | referring to files located in the src tree. | |
424 | ||
425 | $(obj) | |
426 | $(obj) is a relative path which points to the directory | |
427 | where the target is saved. Always use $(obj) when | |
428 | referring to generated files. | |
1da177e4 | 429 | |
cd238eff | 430 | Example:: |
1da177e4 | 431 | |
1da177e4 LT |
432 | #drivers/scsi/Makefile |
433 | $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl | |
434 | $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl | |
435 | ||
cd238eff MCC |
436 | This is a special rule, following the normal syntax |
437 | required by make. | |
438 | ||
439 | The target file depends on two prerequisite files. References | |
440 | to the target file are prefixed with $(obj), references | |
441 | to prerequisites are referenced with $(src) (because they are not | |
442 | generated files). | |
443 | ||
444 | $(kecho) | |
445 | echoing information to user in a rule is often a good practice | |
446 | but when execution "make -s" one does not expect to see any output | |
447 | except for warnings/errors. | |
448 | To support this kbuild defines $(kecho) which will echo out the | |
449 | text following $(kecho) to stdout except if "make -s" is used. | |
450 | ||
451 | Example:: | |
452 | ||
5410ecc0 MF |
453 | #arch/blackfin/boot/Makefile |
454 | $(obj)/vmImage: $(obj)/vmlinux.gz | |
455 | $(call if_changed,uimage) | |
456 | @$(kecho) 'Kernel: $@ is ready' | |
457 | ||
458 | ||
cd238eff MCC |
459 | 3.11 $(CC) support functions |
460 | ---------------------------- | |
20a468b5 | 461 | |
a07f6033 | 462 | The kernel may be built with several different versions of |
20a468b5 | 463 | $(CC), each supporting a unique set of features and options. |
39fed701 | 464 | kbuild provides basic support to check for valid options for $(CC). |
e95be9a5 | 465 | $(CC) is usually the gcc compiler, but other alternatives are |
20a468b5 SR |
466 | available. |
467 | ||
468 | as-option | |
a07f6033 | 469 | as-option is used to check if $(CC) -- when used to compile |
cd238eff | 470 | assembler (`*.S`) files -- supports the given option. An optional |
a07f6033 | 471 | second option may be specified if the first option is not supported. |
20a468b5 | 472 | |
cd238eff MCC |
473 | Example:: |
474 | ||
20a468b5 SR |
475 | #arch/sh/Makefile |
476 | cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),) | |
477 | ||
a07f6033 | 478 | In the above example, cflags-y will be assigned the option |
20a468b5 SR |
479 | -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC). |
480 | The second argument is optional, and if supplied will be used | |
cd238eff MCC |
481 | if first argument is not supported. |
482 | ||
e2414910 AK |
483 | as-instr |
484 | as-instr checks if the assembler reports a specific instruction | |
485 | and then outputs either option1 or option2 | |
486 | C escapes are supported in the test instruction | |
5ef87263 | 487 | Note: as-instr-option uses KBUILD_AFLAGS for assembler options |
e2414910 | 488 | |
20a468b5 | 489 | cc-option |
39fed701 GU |
490 | cc-option is used to check if $(CC) supports a given option, and if |
491 | not supported to use an optional second option. | |
20a468b5 | 492 | |
cd238eff MCC |
493 | Example:: |
494 | ||
25eb650a | 495 | #arch/x86/Makefile |
20a468b5 SR |
496 | cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) |
497 | ||
5c811e59 | 498 | In the above example, cflags-y will be assigned the option |
a07f6033 JE |
499 | -march=pentium-mmx if supported by $(CC), otherwise -march=i586. |
500 | The second argument to cc-option is optional, and if omitted, | |
20a468b5 | 501 | cflags-y will be assigned no value if first option is not supported. |
a0f97e06 | 502 | Note: cc-option uses KBUILD_CFLAGS for $(CC) options |
20a468b5 SR |
503 | |
504 | cc-option-yn | |
39e6e9cf | 505 | cc-option-yn is used to check if gcc supports a given option |
20a468b5 SR |
506 | and return 'y' if supported, otherwise 'n'. |
507 | ||
cd238eff MCC |
508 | Example:: |
509 | ||
20a468b5 SR |
510 | #arch/ppc/Makefile |
511 | biarch := $(call cc-option-yn, -m32) | |
512 | aflags-$(biarch) += -a32 | |
513 | cflags-$(biarch) += -m32 | |
39e6e9cf | 514 | |
a07f6033 JE |
515 | In the above example, $(biarch) is set to y if $(CC) supports the -m32 |
516 | option. When $(biarch) equals 'y', the expanded variables $(aflags-y) | |
517 | and $(cflags-y) will be assigned the values -a32 and -m32, | |
518 | respectively. | |
a0f97e06 | 519 | Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options |
20a468b5 | 520 | |
8417da6f MM |
521 | cc-disable-warning |
522 | cc-disable-warning checks if gcc supports a given warning and returns | |
523 | the commandline switch to disable it. This special function is needed, | |
524 | because gcc 4.4 and later accept any unknown -Wno-* option and only | |
525 | warn about it if there is another warning in the source file. | |
526 | ||
cd238eff MCC |
527 | Example:: |
528 | ||
8417da6f MM |
529 | KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) |
530 | ||
531 | In the above example, -Wno-unused-but-set-variable will be added to | |
532 | KBUILD_CFLAGS only if gcc really accepts it. | |
533 | ||
20a468b5 | 534 | cc-ifversion |
6dcb4e5e MY |
535 | cc-ifversion tests the version of $(CC) and equals the fourth parameter |
536 | if version expression is true, or the fifth (if given) if the version | |
537 | expression is false. | |
20a468b5 | 538 | |
cd238eff MCC |
539 | Example:: |
540 | ||
20a468b5 | 541 | #fs/reiserfs/Makefile |
f77bf014 | 542 | ccflags-y := $(call cc-ifversion, -lt, 0402, -O1) |
20a468b5 | 543 | |
f77bf014 | 544 | In this example, ccflags-y will be assigned the value -O1 if the |
20a468b5 | 545 | $(CC) version is less than 4.2. |
39e6e9cf | 546 | cc-ifversion takes all the shell operators: |
20a468b5 SR |
547 | -eq, -ne, -lt, -le, -gt, and -ge |
548 | The third parameter may be a text as in this example, but it may also | |
549 | be an expanded variable or a macro. | |
550 | ||
910b4046 | 551 | cc-cross-prefix |
631bcfbb | 552 | cc-cross-prefix is used to check if there exists a $(CC) in path with |
910b4046 SR |
553 | one of the listed prefixes. The first prefix where there exist a |
554 | prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found | |
555 | then nothing is returned. | |
556 | Additional prefixes are separated by a single space in the | |
557 | call of cc-cross-prefix. | |
631bcfbb GU |
558 | This functionality is useful for architecture Makefiles that try |
559 | to set CROSS_COMPILE to well-known values but may have several | |
910b4046 | 560 | values to select between. |
631bcfbb GU |
561 | It is recommended only to try to set CROSS_COMPILE if it is a cross |
562 | build (host arch is different from target arch). And if CROSS_COMPILE | |
910b4046 SR |
563 | is already set then leave it with the old value. |
564 | ||
cd238eff MCC |
565 | Example:: |
566 | ||
910b4046 SR |
567 | #arch/m68k/Makefile |
568 | ifneq ($(SUBARCH),$(ARCH)) | |
569 | ifeq ($(CROSS_COMPILE),) | |
570 | CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-) | |
571 | endif | |
572 | endif | |
573 | ||
cd238eff MCC |
574 | 3.12 $(LD) support functions |
575 | ---------------------------- | |
691ef3e7 SR |
576 | |
577 | ld-option | |
578 | ld-option is used to check if $(LD) supports the supplied option. | |
579 | ld-option takes two options as arguments. | |
580 | The second argument is an optional option that can be used if the | |
581 | first option is not supported by $(LD). | |
582 | ||
cd238eff MCC |
583 | Example:: |
584 | ||
691ef3e7 | 585 | #Makefile |
5b83df2b | 586 | LDFLAGS_vmlinux += $(call ld-option, -X) |
691ef3e7 SR |
587 | |
588 | ||
cd238eff MCC |
589 | 4 Host Program support |
590 | ====================== | |
1da177e4 LT |
591 | |
592 | Kbuild supports building executables on the host for use during the | |
593 | compilation stage. | |
594 | Two steps are required in order to use a host executable. | |
595 | ||
596 | The first step is to tell kbuild that a host program exists. This is | |
5f2fb52f | 597 | done utilising the variable "hostprogs". |
1da177e4 LT |
598 | |
599 | The second step is to add an explicit dependency to the executable. | |
39e6e9cf | 600 | This can be done in two ways. Either add the dependency in a rule, |
5f2fb52f | 601 | or utilise the variable "always-y". |
1da177e4 LT |
602 | Both possibilities are described in the following. |
603 | ||
cd238eff MCC |
604 | 4.1 Simple Host Program |
605 | ----------------------- | |
1da177e4 LT |
606 | |
607 | In some cases there is a need to compile and run a program on the | |
608 | computer where the build is running. | |
609 | The following line tells kbuild that the program bin2hex shall be | |
610 | built on the build host. | |
611 | ||
cd238eff MCC |
612 | Example:: |
613 | ||
5f2fb52f | 614 | hostprogs := bin2hex |
1da177e4 LT |
615 | |
616 | Kbuild assumes in the above example that bin2hex is made from a single | |
617 | c-source file named bin2hex.c located in the same directory as | |
618 | the Makefile. | |
39e6e9cf | 619 | |
cd238eff MCC |
620 | 4.2 Composite Host Programs |
621 | --------------------------- | |
1da177e4 LT |
622 | |
623 | Host programs can be made up based on composite objects. | |
624 | The syntax used to define composite objects for host programs is | |
625 | similar to the syntax used for kernel objects. | |
5d3f083d | 626 | $(<executable>-objs) lists all objects used to link the final |
1da177e4 LT |
627 | executable. |
628 | ||
cd238eff MCC |
629 | Example:: |
630 | ||
1da177e4 | 631 | #scripts/lxdialog/Makefile |
5f2fb52f | 632 | hostprogs := lxdialog |
1da177e4 LT |
633 | lxdialog-objs := checklist.o lxdialog.o |
634 | ||
635 | Objects with extension .o are compiled from the corresponding .c | |
a07f6033 | 636 | files. In the above example, checklist.c is compiled to checklist.o |
1da177e4 | 637 | and lxdialog.c is compiled to lxdialog.o. |
cd238eff | 638 | |
a07f6033 | 639 | Finally, the two .o files are linked to the executable, lxdialog. |
1da177e4 LT |
640 | Note: The syntax <executable>-y is not permitted for host-programs. |
641 | ||
cd238eff MCC |
642 | 4.3 Using C++ for host programs |
643 | ------------------------------- | |
1da177e4 LT |
644 | |
645 | kbuild offers support for host programs written in C++. This was | |
646 | introduced solely to support kconfig, and is not recommended | |
647 | for general use. | |
648 | ||
cd238eff MCC |
649 | Example:: |
650 | ||
1da177e4 | 651 | #scripts/kconfig/Makefile |
5f2fb52f | 652 | hostprogs := qconf |
1da177e4 LT |
653 | qconf-cxxobjs := qconf.o |
654 | ||
655 | In the example above the executable is composed of the C++ file | |
656 | qconf.cc - identified by $(qconf-cxxobjs). | |
39e6e9cf | 657 | |
39fed701 | 658 | If qconf is composed of a mixture of .c and .cc files, then an |
1da177e4 LT |
659 | additional line can be used to identify this. |
660 | ||
cd238eff MCC |
661 | Example:: |
662 | ||
1da177e4 | 663 | #scripts/kconfig/Makefile |
5f2fb52f | 664 | hostprogs := qconf |
1da177e4 LT |
665 | qconf-cxxobjs := qconf.o |
666 | qconf-objs := check.o | |
39e6e9cf | 667 | |
cd238eff MCC |
668 | 4.4 Controlling compiler options for host programs |
669 | -------------------------------------------------- | |
1da177e4 LT |
670 | |
671 | When compiling host programs, it is possible to set specific flags. | |
672 | The programs will always be compiled utilising $(HOSTCC) passed | |
96f14fe7 | 673 | the options specified in $(KBUILD_HOSTCFLAGS). |
1da177e4 | 674 | To set flags that will take effect for all host programs created |
a07f6033 | 675 | in that Makefile, use the variable HOST_EXTRACFLAGS. |
1da177e4 | 676 | |
cd238eff MCC |
677 | Example:: |
678 | ||
1da177e4 LT |
679 | #scripts/lxdialog/Makefile |
680 | HOST_EXTRACFLAGS += -I/usr/include/ncurses | |
39e6e9cf | 681 | |
1da177e4 LT |
682 | To set specific flags for a single file the following construction |
683 | is used: | |
684 | ||
cd238eff MCC |
685 | Example:: |
686 | ||
1da177e4 LT |
687 | #arch/ppc64/boot/Makefile |
688 | HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE) | |
39e6e9cf | 689 | |
1da177e4 | 690 | It is also possible to specify additional options to the linker. |
39e6e9cf | 691 | |
cd238eff MCC |
692 | Example:: |
693 | ||
1da177e4 | 694 | #scripts/kconfig/Makefile |
c86b1f93 | 695 | HOSTLDLIBS_qconf := -L$(QTDIR)/lib |
1da177e4 | 696 | |
a07f6033 JE |
697 | When linking qconf, it will be passed the extra option |
698 | "-L$(QTDIR)/lib". | |
39e6e9cf | 699 | |
cd238eff MCC |
700 | 4.5 When host programs are actually built |
701 | ----------------------------------------- | |
1da177e4 LT |
702 | |
703 | Kbuild will only build host-programs when they are referenced | |
704 | as a prerequisite. | |
705 | This is possible in two ways: | |
706 | ||
707 | (1) List the prerequisite explicitly in a special rule. | |
708 | ||
cd238eff MCC |
709 | Example:: |
710 | ||
1da177e4 | 711 | #drivers/pci/Makefile |
5f2fb52f | 712 | hostprogs := gen-devlist |
1da177e4 LT |
713 | $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist |
714 | ( cd $(obj); ./gen-devlist ) < $< | |
715 | ||
39e6e9cf | 716 | The target $(obj)/devlist.h will not be built before |
1da177e4 LT |
717 | $(obj)/gen-devlist is updated. Note that references to |
718 | the host programs in special rules must be prefixed with $(obj). | |
719 | ||
5f2fb52f | 720 | (2) Use always-y |
cd238eff | 721 | |
1da177e4 | 722 | When there is no suitable special rule, and the host program |
5f2fb52f | 723 | shall be built when a makefile is entered, the always-y |
1da177e4 LT |
724 | variable shall be used. |
725 | ||
cd238eff MCC |
726 | Example:: |
727 | ||
1da177e4 | 728 | #scripts/lxdialog/Makefile |
5f2fb52f MY |
729 | hostprogs := lxdialog |
730 | always-y := $(hostprogs) | |
1da177e4 LT |
731 | |
732 | This will tell kbuild to build lxdialog even if not referenced in | |
733 | any rule. | |
734 | ||
cd238eff MCC |
735 | 5 Kbuild clean infrastructure |
736 | ============================= | |
1da177e4 | 737 | |
a07f6033 | 738 | "make clean" deletes most generated files in the obj tree where the kernel |
1da177e4 | 739 | is compiled. This includes generated files such as host programs. |
5f2fb52f MY |
740 | Kbuild knows targets listed in $(hostprogs), $(always-y), $(always-m), |
741 | $(always-), $(extra-y), $(extra-) and $(targets). They are all deleted | |
742 | during "make clean". Files matching the patterns "*.[oas]", "*.ko", plus | |
743 | some additional files generated by kbuild are deleted all over the kernel | |
744 | source tree when "make clean" is executed. | |
1da177e4 | 745 | |
1634f2bf MY |
746 | Additional files or directories can be specified in kbuild makefiles by use of |
747 | $(clean-files). | |
1da177e4 | 748 | |
cd238eff MCC |
749 | Example:: |
750 | ||
97659181 MM |
751 | #lib/Makefile |
752 | clean-files := crc32table.h | |
1da177e4 | 753 | |
bd55daf4 JR |
754 | When executing "make clean", the file "crc32table.h" will be deleted. |
755 | Kbuild will assume files to be in the same relative directory as the | |
97659181 | 756 | Makefile, except if prefixed with $(objtree). |
1da177e4 | 757 | |
1634f2bf MY |
758 | To exclude certain files or directories from make clean, use the |
759 | $(no-clean-files) variable. | |
ef8ff89b | 760 | |
1da177e4 LT |
761 | Usually kbuild descends down in subdirectories due to "obj-* := dir/", |
762 | but in the architecture makefiles where the kbuild infrastructure | |
763 | is not sufficient this sometimes needs to be explicit. | |
764 | ||
cd238eff MCC |
765 | Example:: |
766 | ||
25eb650a | 767 | #arch/x86/boot/Makefile |
eabc8bcb | 768 | subdir- := compressed |
1da177e4 LT |
769 | |
770 | The above assignment instructs kbuild to descend down in the | |
771 | directory compressed/ when "make clean" is executed. | |
772 | ||
39fed701 | 773 | To support the clean infrastructure in the Makefiles that build the |
1da177e4 LT |
774 | final bootimage there is an optional target named archclean: |
775 | ||
cd238eff MCC |
776 | Example:: |
777 | ||
25eb650a | 778 | #arch/x86/Makefile |
1da177e4 | 779 | archclean: |
25eb650a | 780 | $(Q)$(MAKE) $(clean)=arch/x86/boot |
1da177e4 | 781 | |
25eb650a WG |
782 | When "make clean" is executed, make will descend down in arch/x86/boot, |
783 | and clean as usual. The Makefile located in arch/x86/boot/ may use | |
1da177e4 LT |
784 | the subdir- trick to descend further down. |
785 | ||
786 | Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is | |
787 | included in the top level makefile, and the kbuild infrastructure | |
788 | is not operational at that point. | |
789 | ||
790 | Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will | |
791 | be visited during "make clean". | |
792 | ||
cd238eff MCC |
793 | 6 Architecture Makefiles |
794 | ======================== | |
1da177e4 LT |
795 | |
796 | The top level Makefile sets up the environment and does the preparation, | |
797 | before starting to descend down in the individual directories. | |
a07f6033 JE |
798 | The top level makefile contains the generic part, whereas |
799 | arch/$(ARCH)/Makefile contains what is required to set up kbuild | |
800 | for said architecture. | |
801 | To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines | |
1da177e4 LT |
802 | a few targets. |
803 | ||
a07f6033 | 804 | When kbuild executes, the following steps are followed (roughly): |
cd238eff | 805 | |
a07f6033 | 806 | 1) Configuration of the kernel => produce .config |
1da177e4 | 807 | 2) Store kernel version in include/linux/version.h |
b22ae40e | 808 | 3) Updating all other prerequisites to the target prepare: |
1da177e4 | 809 | - Additional prerequisites are specified in arch/$(ARCH)/Makefile |
b22ae40e | 810 | 4) Recursively descend down in all directories listed in |
1da177e4 | 811 | init-* core* drivers-* net-* libs-* and build all targets. |
a07f6033 | 812 | - The values of the above variables are expanded in arch/$(ARCH)/Makefile. |
b22ae40e | 813 | 5) All object files are then linked and the resulting file vmlinux is |
a07f6033 | 814 | located at the root of the obj tree. |
1da177e4 LT |
815 | The very first objects linked are listed in head-y, assigned by |
816 | arch/$(ARCH)/Makefile. | |
b22ae40e | 817 | 6) Finally, the architecture-specific part does any required post processing |
1da177e4 LT |
818 | and builds the final bootimage. |
819 | - This includes building boot records | |
5c811e59 | 820 | - Preparing initrd images and the like |
1da177e4 LT |
821 | |
822 | ||
cd238eff MCC |
823 | 6.1 Set variables to tweak the build to the architecture |
824 | -------------------------------------------------------- | |
1da177e4 | 825 | |
cd238eff MCC |
826 | LDFLAGS |
827 | Generic $(LD) options | |
1da177e4 LT |
828 | |
829 | Flags used for all invocations of the linker. | |
830 | Often specifying the emulation is sufficient. | |
831 | ||
cd238eff MCC |
832 | Example:: |
833 | ||
1da177e4 LT |
834 | #arch/s390/Makefile |
835 | LDFLAGS := -m elf_s390 | |
cd238eff | 836 | |
f77bf014 | 837 | Note: ldflags-y can be used to further customise |
a9af3305 | 838 | the flags used. See chapter 3.7. |
39e6e9cf | 839 | |
cd238eff MCC |
840 | LDFLAGS_vmlinux |
841 | Options for $(LD) when linking vmlinux | |
1da177e4 LT |
842 | |
843 | LDFLAGS_vmlinux is used to specify additional flags to pass to | |
a07f6033 | 844 | the linker when linking the final vmlinux image. |
1da177e4 LT |
845 | LDFLAGS_vmlinux uses the LDFLAGS_$@ support. |
846 | ||
cd238eff MCC |
847 | Example:: |
848 | ||
25eb650a | 849 | #arch/x86/Makefile |
1da177e4 LT |
850 | LDFLAGS_vmlinux := -e stext |
851 | ||
cd238eff MCC |
852 | OBJCOPYFLAGS |
853 | objcopy flags | |
1da177e4 LT |
854 | |
855 | When $(call if_changed,objcopy) is used to translate a .o file, | |
a07f6033 | 856 | the flags specified in OBJCOPYFLAGS will be used. |
1da177e4 LT |
857 | $(call if_changed,objcopy) is often used to generate raw binaries on |
858 | vmlinux. | |
859 | ||
cd238eff MCC |
860 | Example:: |
861 | ||
1da177e4 LT |
862 | #arch/s390/Makefile |
863 | OBJCOPYFLAGS := -O binary | |
864 | ||
865 | #arch/s390/boot/Makefile | |
866 | $(obj)/image: vmlinux FORCE | |
867 | $(call if_changed,objcopy) | |
868 | ||
a07f6033 | 869 | In this example, the binary $(obj)/image is a binary version of |
1da177e4 LT |
870 | vmlinux. The usage of $(call if_changed,xxx) will be described later. |
871 | ||
cd238eff | 872 | KBUILD_AFLAGS |
5ef87263 | 873 | Assembler flags |
1da177e4 LT |
874 | |
875 | Default value - see top level Makefile | |
876 | Append or modify as required per architecture. | |
877 | ||
cd238eff MCC |
878 | Example:: |
879 | ||
1da177e4 | 880 | #arch/sparc64/Makefile |
222d394d | 881 | KBUILD_AFLAGS += -m64 -mcpu=ultrasparc |
1da177e4 | 882 | |
cd238eff MCC |
883 | KBUILD_CFLAGS |
884 | $(CC) compiler flags | |
1da177e4 LT |
885 | |
886 | Default value - see top level Makefile | |
887 | Append or modify as required per architecture. | |
888 | ||
a0f97e06 | 889 | Often, the KBUILD_CFLAGS variable depends on the configuration. |
1da177e4 | 890 | |
cd238eff MCC |
891 | Example:: |
892 | ||
ff4eb04c PB |
893 | #arch/x86/boot/compressed/Makefile |
894 | cflags-$(CONFIG_X86_32) := -march=i386 | |
895 | cflags-$(CONFIG_X86_64) := -mcmodel=small | |
a0f97e06 | 896 | KBUILD_CFLAGS += $(cflags-y) |
1da177e4 LT |
897 | |
898 | Many arch Makefiles dynamically run the target C compiler to | |
cd238eff | 899 | probe supported options:: |
1da177e4 | 900 | |
25eb650a | 901 | #arch/x86/Makefile |
1da177e4 LT |
902 | |
903 | ... | |
904 | cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ | |
905 | -march=pentium2,-march=i686) | |
906 | ... | |
907 | # Disable unit-at-a-time mode ... | |
a0f97e06 | 908 | KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time) |
1da177e4 LT |
909 | ... |
910 | ||
911 | ||
a07f6033 | 912 | The first example utilises the trick that a config option expands |
1da177e4 LT |
913 | to 'y' when selected. |
914 | ||
cd238eff | 915 | KBUILD_AFLAGS_KERNEL |
5ef87263 | 916 | Assembler options specific for built-in |
1da177e4 | 917 | |
80c00ba9 | 918 | $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile |
1da177e4 LT |
919 | resident kernel code. |
920 | ||
cd238eff | 921 | KBUILD_AFLAGS_MODULE |
5ef87263 | 922 | Assembler options specific for modules |
1da177e4 | 923 | |
39fed701 | 924 | $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that |
5ef87263 | 925 | are used for assembler. |
cd238eff | 926 | |
2eebb7ab | 927 | From commandline AFLAGS_MODULE shall be used (see kbuild.rst). |
1da177e4 | 928 | |
cd238eff MCC |
929 | KBUILD_CFLAGS_KERNEL |
930 | $(CC) options specific for built-in | |
80c00ba9 SR |
931 | |
932 | $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile | |
933 | resident kernel code. | |
934 | ||
cd238eff MCC |
935 | KBUILD_CFLAGS_MODULE |
936 | Options for $(CC) when building modules | |
6588169d | 937 | |
39fed701 | 938 | $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that |
6588169d | 939 | are used for $(CC). |
2eebb7ab | 940 | From commandline CFLAGS_MODULE shall be used (see kbuild.rst). |
6588169d | 941 | |
cd238eff MCC |
942 | KBUILD_LDFLAGS_MODULE |
943 | Options for $(LD) when linking modules | |
6588169d | 944 | |
39fed701 | 945 | $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options |
6588169d | 946 | used when linking modules. This is often a linker script. |
cd238eff | 947 | |
2eebb7ab | 948 | From commandline LDFLAGS_MODULE shall be used (see kbuild.rst). |
39e6e9cf | 949 | |
888f0c34 MY |
950 | KBUILD_LDS |
951 | ||
952 | The linker script with full path. Assigned by the top-level Makefile. | |
953 | ||
10df0638 MY |
954 | KBUILD_LDS_MODULE |
955 | ||
956 | The module linker script with full path. Assigned by the top-level | |
957 | Makefile and additionally by the arch Makefile. | |
958 | ||
888f0c34 MY |
959 | KBUILD_VMLINUX_OBJS |
960 | ||
961 | All object files for vmlinux. They are linked to vmlinux in the same | |
962 | order as listed in KBUILD_VMLINUX_OBJS. | |
963 | ||
964 | KBUILD_VMLINUX_LIBS | |
965 | ||
966 | All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and | |
967 | KBUILD_VMLINUX_LIBS together specify all the object files used to | |
968 | link vmlinux. | |
61754c18 | 969 | |
cd238eff MCC |
970 | 6.2 Add prerequisites to archheaders |
971 | ------------------------------------ | |
052ad274 PA |
972 | |
973 | The archheaders: rule is used to generate header files that | |
f3c8d4c7 | 974 | may be installed into user space by "make header_install". |
052ad274 PA |
975 | |
976 | It is run before "make archprepare" when run on the | |
977 | architecture itself. | |
978 | ||
979 | ||
cd238eff MCC |
980 | 6.3 Add prerequisites to archprepare |
981 | ------------------------------------ | |
1da177e4 | 982 | |
a07f6033 | 983 | The archprepare: rule is used to list prerequisites that need to be |
1da177e4 | 984 | built before starting to descend down in the subdirectories. |
a07f6033 | 985 | This is usually used for header files containing assembler constants. |
1da177e4 | 986 | |
cd238eff MCC |
987 | Example:: |
988 | ||
5bb78269 SR |
989 | #arch/arm/Makefile |
990 | archprepare: maketools | |
1da177e4 | 991 | |
a07f6033 | 992 | In this example, the file target maketools will be processed |
5bb78269 | 993 | before descending down in the subdirectories. |
1da177e4 LT |
994 | See also chapter XXX-TODO that describe how kbuild supports |
995 | generating offset header files. | |
996 | ||
997 | ||
cd238eff MCC |
998 | 6.4 List directories to visit when descending |
999 | --------------------------------------------- | |
1da177e4 LT |
1000 | |
1001 | An arch Makefile cooperates with the top Makefile to define variables | |
1002 | which specify how to build the vmlinux file. Note that there is no | |
1003 | corresponding arch-specific section for modules; the module-building | |
1004 | machinery is all architecture-independent. | |
1005 | ||
39e6e9cf | 1006 | |
cd238eff MCC |
1007 | head-y, init-y, core-y, libs-y, drivers-y, net-y |
1008 | $(head-y) lists objects to be linked first in vmlinux. | |
1009 | ||
1010 | $(libs-y) lists directories where a lib.a archive can be located. | |
1011 | ||
1012 | The rest list directories where a built-in.a object file can be | |
1013 | located. | |
1da177e4 | 1014 | |
cd238eff | 1015 | $(init-y) objects will be located after $(head-y). |
1da177e4 | 1016 | |
cd238eff | 1017 | Then the rest follows in this order: |
1da177e4 | 1018 | |
cd238eff MCC |
1019 | $(core-y), $(libs-y), $(drivers-y) and $(net-y). |
1020 | ||
1021 | The top level Makefile defines values for all generic directories, | |
1022 | and arch/$(ARCH)/Makefile only adds architecture-specific | |
1023 | directories. | |
1024 | ||
1025 | Example:: | |
1da177e4 | 1026 | |
1da177e4 LT |
1027 | #arch/sparc64/Makefile |
1028 | core-y += arch/sparc64/kernel/ | |
1029 | libs-y += arch/sparc64/prom/ arch/sparc64/lib/ | |
1030 | drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ | |
1031 | ||
1032 | ||
cd238eff MCC |
1033 | 6.5 Architecture-specific boot images |
1034 | ------------------------------------- | |
1da177e4 LT |
1035 | |
1036 | An arch Makefile specifies goals that take the vmlinux file, compress | |
1037 | it, wrap it in bootstrapping code, and copy the resulting files | |
1038 | somewhere. This includes various kinds of installation commands. | |
1039 | The actual goals are not standardized across architectures. | |
1040 | ||
1041 | It is common to locate any additional processing in a boot/ | |
1042 | directory below arch/$(ARCH)/. | |
1043 | ||
1044 | Kbuild does not provide any smart way to support building a | |
1045 | target specified in boot/. Therefore arch/$(ARCH)/Makefile shall | |
1046 | call make manually to build a target in boot/. | |
1047 | ||
1048 | The recommended approach is to include shortcuts in | |
1049 | arch/$(ARCH)/Makefile, and use the full path when calling down | |
1050 | into the arch/$(ARCH)/boot/Makefile. | |
1051 | ||
cd238eff MCC |
1052 | Example:: |
1053 | ||
25eb650a WG |
1054 | #arch/x86/Makefile |
1055 | boot := arch/x86/boot | |
1da177e4 LT |
1056 | bzImage: vmlinux |
1057 | $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ | |
1058 | ||
1059 | "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke | |
1060 | make in a subdirectory. | |
1061 | ||
5c811e59 | 1062 | There are no rules for naming architecture-specific targets, |
1da177e4 | 1063 | but executing "make help" will list all relevant targets. |
a07f6033 | 1064 | To support this, $(archhelp) must be defined. |
1da177e4 | 1065 | |
cd238eff MCC |
1066 | Example:: |
1067 | ||
25eb650a | 1068 | #arch/x86/Makefile |
1da177e4 LT |
1069 | define archhelp |
1070 | echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)' | |
39e6e9cf | 1071 | endif |
1da177e4 LT |
1072 | |
1073 | When make is executed without arguments, the first goal encountered | |
1074 | will be built. In the top level Makefile the first goal present | |
1075 | is all:. | |
a07f6033 JE |
1076 | An architecture shall always, per default, build a bootable image. |
1077 | In "make help", the default goal is highlighted with a '*'. | |
1da177e4 LT |
1078 | Add a new prerequisite to all: to select a default goal different |
1079 | from vmlinux. | |
1080 | ||
cd238eff MCC |
1081 | Example:: |
1082 | ||
25eb650a | 1083 | #arch/x86/Makefile |
39e6e9cf | 1084 | all: bzImage |
1da177e4 LT |
1085 | |
1086 | When "make" is executed without arguments, bzImage will be built. | |
1087 | ||
cd238eff MCC |
1088 | 6.6 Building non-kbuild targets |
1089 | ------------------------------- | |
1da177e4 LT |
1090 | |
1091 | extra-y | |
39fed701 | 1092 | extra-y specifies additional targets created in the current |
cd238eff | 1093 | directory, in addition to any targets specified by `obj-*`. |
1da177e4 LT |
1094 | |
1095 | Listing all targets in extra-y is required for two purposes: | |
cd238eff | 1096 | |
1da177e4 | 1097 | 1) Enable kbuild to check changes in command lines |
cd238eff | 1098 | |
1da177e4 | 1099 | - When $(call if_changed,xxx) is used |
cd238eff | 1100 | |
1da177e4 LT |
1101 | 2) kbuild knows what files to delete during "make clean" |
1102 | ||
cd238eff MCC |
1103 | Example:: |
1104 | ||
25eb650a | 1105 | #arch/x86/kernel/Makefile |
1da177e4 LT |
1106 | extra-y := head.o init_task.o |
1107 | ||
a07f6033 | 1108 | In this example, extra-y is used to list object files that |
f49821ee | 1109 | shall be built, but shall not be linked as part of built-in.a. |
1da177e4 | 1110 | |
cd238eff MCC |
1111 | 6.7 Commands useful for building a boot image |
1112 | --------------------------------------------- | |
1da177e4 | 1113 | |
cd238eff MCC |
1114 | Kbuild provides a few macros that are useful when building a |
1115 | boot image. | |
1da177e4 LT |
1116 | |
1117 | if_changed | |
1da177e4 LT |
1118 | if_changed is the infrastructure used for the following commands. |
1119 | ||
cd238eff MCC |
1120 | Usage:: |
1121 | ||
1da177e4 | 1122 | target: source(s) FORCE |
ef80f0a1 | 1123 | $(call if_changed,ld/objcopy/gzip/...) |
1da177e4 | 1124 | |
a07f6033 | 1125 | When the rule is evaluated, it is checked to see if any files |
5c811e59 | 1126 | need an update, or the command line has changed since the last |
1da177e4 LT |
1127 | invocation. The latter will force a rebuild if any options |
1128 | to the executable have changed. | |
1129 | Any target that utilises if_changed must be listed in $(targets), | |
1130 | otherwise the command line check will fail, and the target will | |
1131 | always be built. | |
1132 | Assignments to $(targets) are without $(obj)/ prefix. | |
1133 | if_changed may be used in conjunction with custom commands as | |
052ad274 | 1134 | defined in 6.8 "Custom kbuild commands". |
49490571 | 1135 | |
1da177e4 | 1136 | Note: It is a typical mistake to forget the FORCE prerequisite. |
49490571 PBG |
1137 | Another common pitfall is that whitespace is sometimes |
1138 | significant; for instance, the below will fail (note the extra space | |
cd238eff MCC |
1139 | after the comma):: |
1140 | ||
49490571 | 1141 | target: source(s) FORCE |
1da177e4 | 1142 | |
cd238eff MCC |
1143 | **WRONG!** $(call if_changed, ld/objcopy/gzip/...) |
1144 | ||
1145 | Note: | |
1146 | if_changed should not be used more than once per target. | |
bb81955f | 1147 | It stores the executed command in a corresponding .cmd |
cd238eff | 1148 | |
bb81955f DG |
1149 | file and multiple calls would result in overwrites and |
1150 | unwanted results when the target is up to date and only the | |
1151 | tests on changed commands trigger execution of commands. | |
1152 | ||
1da177e4 | 1153 | ld |
a07f6033 | 1154 | Link target. Often, LDFLAGS_$@ is used to set specific options to ld. |
39e6e9cf | 1155 | |
cd238eff MCC |
1156 | Example:: |
1157 | ||
25eb650a | 1158 | #arch/x86/boot/Makefile |
1da177e4 LT |
1159 | LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary |
1160 | LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext | |
1161 | ||
1162 | targets += setup setup.o bootsect bootsect.o | |
1163 | $(obj)/setup $(obj)/bootsect: %: %.o FORCE | |
1164 | $(call if_changed,ld) | |
1165 | ||
a07f6033 JE |
1166 | In this example, there are two possible targets, requiring different |
1167 | options to the linker. The linker options are specified using the | |
1da177e4 | 1168 | LDFLAGS_$@ syntax - one for each potential target. |
5d3f083d | 1169 | $(targets) are assigned all potential targets, by which kbuild knows |
1da177e4 | 1170 | the targets and will: |
cd238eff | 1171 | |
1da177e4 LT |
1172 | 1) check for commandline changes |
1173 | 2) delete target during make clean | |
1174 | ||
1175 | The ": %: %.o" part of the prerequisite is a shorthand that | |
39fed701 | 1176 | frees us from listing the setup.o and bootsect.o files. |
cd238eff MCC |
1177 | |
1178 | Note: | |
1179 | It is a common mistake to forget the "targets :=" assignment, | |
1da177e4 LT |
1180 | resulting in the target file being recompiled for no |
1181 | obvious reason. | |
1182 | ||
d87e47e1 C |
1183 | objcopy |
1184 | Copy binary. Uses OBJCOPYFLAGS usually specified in | |
1185 | arch/$(ARCH)/Makefile. | |
1186 | OBJCOPYFLAGS_$@ may be used to set additional options. | |
1187 | ||
1188 | gzip | |
1189 | Compress target. Use maximum compression to compress target. | |
1190 | ||
cd238eff MCC |
1191 | Example:: |
1192 | ||
d87e47e1 C |
1193 | #arch/x86/boot/compressed/Makefile |
1194 | $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE | |
1195 | $(call if_changed,gzip) | |
1196 | ||
aab94339 | 1197 | dtc |
c1410562 | 1198 | Create flattened device tree blob object suitable for linking |
aab94339 DB |
1199 | into vmlinux. Device tree blobs linked into vmlinux are placed |
1200 | in an init section in the image. Platform code *must* copy the | |
1201 | blob to non-init memory prior to calling unflatten_device_tree(). | |
1202 | ||
cd238eff MCC |
1203 | To use this command, simply add `*.dtb` into obj-y or targets, or make |
1204 | some other target depend on `%.dtb` | |
aab94339 | 1205 | |
cd238eff | 1206 | A central rule exists to create `$(obj)/%.dtb` from `$(src)/%.dts`; |
90b335fb | 1207 | architecture Makefiles do no need to explicitly write out that rule. |
aab94339 | 1208 | |
cd238eff MCC |
1209 | Example:: |
1210 | ||
90b335fb | 1211 | targets += $(dtb-y) |
90b335fb | 1212 | DTC_FLAGS ?= -p 1024 |
1da177e4 | 1213 | |
cd238eff MCC |
1214 | 6.8 Custom kbuild commands |
1215 | -------------------------- | |
1da177e4 | 1216 | |
a07f6033 | 1217 | When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand |
1da177e4 LT |
1218 | of a command is normally displayed. |
1219 | To enable this behaviour for custom commands kbuild requires | |
cd238eff MCC |
1220 | two variables to be set:: |
1221 | ||
1222 | quiet_cmd_<command> - what shall be echoed | |
1223 | cmd_<command> - the command to execute | |
1224 | ||
1225 | Example:: | |
1da177e4 | 1226 | |
1da177e4 LT |
1227 | # |
1228 | quiet_cmd_image = BUILD $@ | |
1229 | cmd_image = $(obj)/tools/build $(BUILDFLAGS) \ | |
1230 | $(obj)/vmlinux.bin > $@ | |
1231 | ||
1232 | targets += bzImage | |
1233 | $(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE | |
1234 | $(call if_changed,image) | |
1235 | @echo 'Kernel: $@ is ready' | |
1236 | ||
cd238eff | 1237 | When updating the $(obj)/bzImage target, the line: |
1da177e4 | 1238 | |
cd238eff | 1239 | BUILD arch/x86/boot/bzImage |
1da177e4 LT |
1240 | |
1241 | will be displayed with "make KBUILD_VERBOSE=0". | |
39e6e9cf | 1242 | |
1da177e4 | 1243 | |
ff4634ee MY |
1244 | 6.9 Preprocessing linker scripts |
1245 | -------------------------------- | |
1da177e4 | 1246 | |
a07f6033 | 1247 | When the vmlinux image is built, the linker script |
1da177e4 LT |
1248 | arch/$(ARCH)/kernel/vmlinux.lds is used. |
1249 | The script is a preprocessed variant of the file vmlinux.lds.S | |
1250 | located in the same directory. | |
cd238eff MCC |
1251 | kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`. |
1252 | ||
1253 | Example:: | |
39e6e9cf | 1254 | |
25eb650a | 1255 | #arch/x86/kernel/Makefile |
faa7bdd7 | 1256 | extra-y := vmlinux.lds |
39e6e9cf | 1257 | |
1da177e4 LT |
1258 | #Makefile |
1259 | export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH) | |
39e6e9cf | 1260 | |
faa7bdd7 | 1261 | The assignment to extra-y is used to tell kbuild to build the |
a07f6033 JE |
1262 | target vmlinux.lds. |
1263 | The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the | |
1da177e4 | 1264 | specified options when building the target vmlinux.lds. |
39e6e9cf | 1265 | |
cd238eff MCC |
1266 | When building the `*.lds` target, kbuild uses the variables:: |
1267 | ||
1268 | KBUILD_CPPFLAGS : Set in top-level Makefile | |
1269 | cppflags-y : May be set in the kbuild makefile | |
1270 | CPPFLAGS_$(@F) : Target-specific flags. | |
1271 | Note that the full filename is used in this | |
1272 | assignment. | |
1da177e4 | 1273 | |
cd238eff | 1274 | The kbuild infrastructure for `*lds` files is used in several |
5c811e59 | 1275 | architecture-specific files. |
1da177e4 | 1276 | |
cd238eff MCC |
1277 | 6.10 Generic header files |
1278 | ------------------------- | |
d8ecc5cd SR |
1279 | |
1280 | The directory include/asm-generic contains the header files | |
1281 | that may be shared between individual architectures. | |
1282 | The recommended approach how to use a generic header file is | |
1283 | to list the file in the Kbuild file. | |
d87e47e1 | 1284 | See "7.2 generic-y" for further info on syntax etc. |
d8ecc5cd | 1285 | |
cd238eff MCC |
1286 | 6.11 Post-link pass |
1287 | ------------------- | |
fbe6e37d NP |
1288 | |
1289 | If the file arch/xxx/Makefile.postlink exists, this makefile | |
1290 | will be invoked for post-link objects (vmlinux and modules.ko) | |
1291 | for architectures to run post-link passes on. Must also handle | |
1292 | the clean target. | |
1293 | ||
1294 | This pass runs after kallsyms generation. If the architecture | |
1295 | needs to modify symbol locations, rather than manipulate the | |
1296 | kallsyms, it may be easier to add another postlink target for | |
1297 | .tmp_vmlinux? targets to be called from link-vmlinux.sh. | |
1298 | ||
1299 | For example, powerpc uses this to check relocation sanity of | |
1300 | the linked vmlinux file. | |
1301 | ||
cd238eff MCC |
1302 | 7 Kbuild syntax for exported headers |
1303 | ------------------------------------ | |
c7bb349e | 1304 | |
39fed701 | 1305 | The kernel includes a set of headers that is exported to userspace. |
c95940f2 | 1306 | Many headers can be exported as-is but other headers require a |
c7bb349e SR |
1307 | minimal pre-processing before they are ready for user-space. |
1308 | The pre-processing does: | |
cd238eff | 1309 | |
39fed701 | 1310 | - drop kernel-specific annotations |
c7bb349e | 1311 | - drop include of compiler.h |
cd238eff | 1312 | - drop all sections that are kernel internal (guarded by `ifdef __KERNEL__`) |
c7bb349e | 1313 | |
fcc8487d | 1314 | All headers under include/uapi/, include/generated/uapi/, |
61562f98 | 1315 | arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/ |
fcc8487d | 1316 | are exported. |
c7bb349e | 1317 | |
fcc8487d ND |
1318 | A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and |
1319 | arch/<arch>/include/asm/ to list asm files coming from asm-generic. | |
1320 | See subsequent chapter for the syntax of the Kbuild file. | |
c7bb349e | 1321 | |
cd238eff MCC |
1322 | 7.1 no-export-headers |
1323 | --------------------- | |
c7bb349e | 1324 | |
fcc8487d ND |
1325 | no-export-headers is essentially used by include/uapi/linux/Kbuild to |
1326 | avoid exporting specific headers (e.g. kvm.h) on architectures that do | |
1327 | not support it. It should be avoided as much as possible. | |
c7bb349e | 1328 | |
cd238eff MCC |
1329 | 7.2 generic-y |
1330 | ------------- | |
d8ecc5cd SR |
1331 | |
1332 | If an architecture uses a verbatim copy of a header from | |
1333 | include/asm-generic then this is listed in the file | |
1334 | arch/$(ARCH)/include/asm/Kbuild like this: | |
1335 | ||
cd238eff MCC |
1336 | Example:: |
1337 | ||
d8ecc5cd SR |
1338 | #arch/x86/include/asm/Kbuild |
1339 | generic-y += termios.h | |
1340 | generic-y += rtc.h | |
1341 | ||
1342 | During the prepare phase of the build a wrapper include | |
cd238eff | 1343 | file is generated in the directory:: |
d8ecc5cd SR |
1344 | |
1345 | arch/$(ARCH)/include/generated/asm | |
1346 | ||
1347 | When a header is exported where the architecture uses | |
1348 | the generic header a similar wrapper is generated as part | |
cd238eff | 1349 | of the set of exported headers in the directory:: |
d8ecc5cd SR |
1350 | |
1351 | usr/include/asm | |
1352 | ||
1353 | The generated wrapper will in both cases look like the following: | |
1354 | ||
cd238eff MCC |
1355 | Example: termios.h:: |
1356 | ||
d8ecc5cd | 1357 | #include <asm-generic/termios.h> |
c7bb349e | 1358 | |
cd238eff MCC |
1359 | 7.3 generated-y |
1360 | --------------- | |
54b880ca JH |
1361 | |
1362 | If an architecture generates other header files alongside generic-y | |
ae3f4151 | 1363 | wrappers, generated-y specifies them. |
54b880ca JH |
1364 | |
1365 | This prevents them being treated as stale asm-generic wrappers and | |
1366 | removed. | |
1367 | ||
cd238eff MCC |
1368 | Example:: |
1369 | ||
54b880ca JH |
1370 | #arch/x86/include/asm/Kbuild |
1371 | generated-y += syscalls_32.h | |
1372 | ||
cd238eff MCC |
1373 | 7.4 mandatory-y |
1374 | --------------- | |
fcc8487d | 1375 | |
037fc336 | 1376 | mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild |
91998731 MY |
1377 | to define the minimum set of ASM headers that all architectures must have. |
1378 | ||
1379 | This works like optional generic-y. If a mandatory header is missing | |
1380 | in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate | |
1381 | a wrapper of the asm-generic one. | |
fcc8487d | 1382 | |
cd238eff MCC |
1383 | 8 Kbuild Variables |
1384 | ================== | |
1da177e4 LT |
1385 | |
1386 | The top Makefile exports the following variables: | |
1387 | ||
1388 | VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION | |
1da177e4 LT |
1389 | These variables define the current kernel version. A few arch |
1390 | Makefiles actually use these values directly; they should use | |
1391 | $(KERNELRELEASE) instead. | |
1392 | ||
1393 | $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic | |
1394 | three-part version number, such as "2", "4", and "0". These three | |
1395 | values are always numeric. | |
1396 | ||
1397 | $(EXTRAVERSION) defines an even tinier sublevel for pre-patches | |
1398 | or additional patches. It is usually some non-numeric string | |
1399 | such as "-pre4", and is often blank. | |
1400 | ||
1401 | KERNELRELEASE | |
1da177e4 LT |
1402 | $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable |
1403 | for constructing installation directory names or showing in | |
1404 | version strings. Some arch Makefiles use it for this purpose. | |
1405 | ||
1406 | ARCH | |
1da177e4 LT |
1407 | This variable defines the target architecture, such as "i386", |
1408 | "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to | |
1409 | determine which files to compile. | |
1410 | ||
1411 | By default, the top Makefile sets $(ARCH) to be the same as the | |
1412 | host system architecture. For a cross build, a user may | |
cd238eff | 1413 | override the value of $(ARCH) on the command line:: |
1da177e4 LT |
1414 | |
1415 | make ARCH=m68k ... | |
1416 | ||
1417 | ||
1418 | INSTALL_PATH | |
1da177e4 LT |
1419 | This variable defines a place for the arch Makefiles to install |
1420 | the resident kernel image and System.map file. | |
5c811e59 | 1421 | Use this for architecture-specific install targets. |
1da177e4 LT |
1422 | |
1423 | INSTALL_MOD_PATH, MODLIB | |
1da177e4 LT |
1424 | $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module |
1425 | installation. This variable is not defined in the Makefile but | |
1426 | may be passed in by the user if desired. | |
1427 | ||
1428 | $(MODLIB) specifies the directory for module installation. | |
1429 | The top Makefile defines $(MODLIB) to | |
1430 | $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may | |
1431 | override this value on the command line if desired. | |
1432 | ||
ac031f26 | 1433 | INSTALL_MOD_STRIP |
39fed701 | 1434 | If this variable is specified, it will cause modules to be stripped |
ac031f26 | 1435 | after they are installed. If INSTALL_MOD_STRIP is '1', then the |
39fed701 | 1436 | default option --strip-debug will be used. Otherwise, the |
177b241d GE |
1437 | INSTALL_MOD_STRIP value will be used as the option(s) to the strip |
1438 | command. | |
ac031f26 TT |
1439 | |
1440 | ||
cd238eff MCC |
1441 | 9 Makefile language |
1442 | =================== | |
1da177e4 | 1443 | |
a07f6033 | 1444 | The kernel Makefiles are designed to be run with GNU Make. The Makefiles |
1da177e4 LT |
1445 | use only the documented features of GNU Make, but they do use many |
1446 | GNU extensions. | |
1447 | ||
1448 | GNU Make supports elementary list-processing functions. The kernel | |
1449 | Makefiles use a novel style of list building and manipulation with few | |
1450 | "if" statements. | |
1451 | ||
1452 | GNU Make has two assignment operators, ":=" and "=". ":=" performs | |
1453 | immediate evaluation of the right-hand side and stores an actual string | |
1454 | into the left-hand side. "=" is like a formula definition; it stores the | |
1455 | right-hand side in an unevaluated form and then evaluates this form each | |
1456 | time the left-hand side is used. | |
1457 | ||
1458 | There are some cases where "=" is appropriate. Usually, though, ":=" | |
1459 | is the right choice. | |
1460 | ||
cd238eff MCC |
1461 | 10 Credits |
1462 | ========== | |
1da177e4 | 1463 | |
cd238eff MCC |
1464 | - Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> |
1465 | - Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de> | |
1466 | - Updates by Sam Ravnborg <sam@ravnborg.org> | |
1467 | - Language QA by Jan Engelhardt <jengelh@gmx.de> | |
1da177e4 | 1468 | |
cd238eff MCC |
1469 | 11 TODO |
1470 | ======= | |
1da177e4 | 1471 | |
a07f6033 | 1472 | - Describe how kbuild supports shipped files with _shipped. |
1da177e4 LT |
1473 | - Generating offset header files. |
1474 | - Add more variables to section 7? |