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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 | |
3d277907 | 15 | --- 3.4 <deleted> |
1da177e4 LT |
16 | --- 3.5 Library file goals - lib-y |
17 | --- 3.6 Descending down in directories | |
d0e628cd MY |
18 | --- 3.7 Non-builtin vmlinux targets - extra-y |
19 | --- 3.8 Always built goals - always-y | |
20 | --- 3.9 Compilation flags | |
21 | --- 3.10 Dependency tracking | |
22 | --- 3.11 Custom Rules | |
23 | --- 3.12 Command change detection | |
24 | --- 3.13 $(CC) support functions | |
25 | --- 3.14 $(LD) support functions | |
26 | --- 3.15 Script Invocation | |
1da177e4 LT |
27 | |
28 | === 4 Host Program support | |
29 | --- 4.1 Simple Host Program | |
30 | --- 4.2 Composite Host Programs | |
62e22107 MY |
31 | --- 4.3 Using C++ for host programs |
32 | --- 4.4 Controlling compiler options for host programs | |
33 | --- 4.5 When host programs are actually built | |
1da177e4 | 34 | |
e079a08c MY |
35 | === 5 Userspace Program support |
36 | --- 5.1 Simple Userspace Program | |
37 | --- 5.2 Composite Userspace Programs | |
38 | --- 5.3 Controlling compiler options for userspace programs | |
39 | --- 5.4 When userspace programs are actually built | |
40 | ||
41 | === 6 Kbuild clean infrastructure | |
42 | ||
43 | === 7 Architecture Makefiles | |
44 | --- 7.1 Set variables to tweak the build to the architecture | |
b26ff488 RD |
45 | --- 7.2 Add prerequisites to archheaders |
46 | --- 7.3 Add prerequisites to archprepare | |
e079a08c MY |
47 | --- 7.4 List directories to visit when descending |
48 | --- 7.5 Architecture-specific boot images | |
49 | --- 7.6 Building non-kbuild targets | |
50 | --- 7.7 Commands useful for building a boot image | |
41cac083 | 51 | --- 7.8 <deleted> |
e079a08c MY |
52 | --- 7.9 Preprocessing linker scripts |
53 | --- 7.10 Generic header files | |
54 | --- 7.11 Post-link pass | |
55 | ||
56 | === 8 Kbuild syntax for exported headers | |
57 | --- 8.1 no-export-headers | |
58 | --- 8.2 generic-y | |
59 | --- 8.3 generated-y | |
60 | --- 8.4 mandatory-y | |
61 | ||
62 | === 9 Kbuild Variables | |
63 | === 10 Makefile language | |
64 | === 11 Credits | |
65 | === 12 TODO | |
1da177e4 | 66 | |
cd238eff MCC |
67 | 1 Overview |
68 | ========== | |
1da177e4 | 69 | |
cd238eff | 70 | The Makefiles have five parts:: |
1da177e4 | 71 | |
8c4d9b14 MY |
72 | Makefile the top Makefile. |
73 | .config the kernel configuration file. | |
74 | arch/$(SRCARCH)/Makefile the arch Makefile. | |
75 | scripts/Makefile.* common rules etc. for all kbuild Makefiles. | |
76 | kbuild Makefiles exist in every subdirectory | |
1da177e4 LT |
77 | |
78 | The top Makefile reads the .config file, which comes from the kernel | |
79 | configuration process. | |
80 | ||
81 | The top Makefile is responsible for building two major products: vmlinux | |
82 | (the resident kernel image) and modules (any module files). | |
83 | It builds these goals by recursively descending into the subdirectories of | |
84 | the kernel source tree. | |
85 | The list of subdirectories which are visited depends upon the kernel | |
86 | configuration. The top Makefile textually includes an arch Makefile | |
8c4d9b14 | 87 | with the name arch/$(SRCARCH)/Makefile. The arch Makefile supplies |
1da177e4 LT |
88 | architecture-specific information to the top Makefile. |
89 | ||
90 | Each subdirectory has a kbuild Makefile which carries out the commands | |
91 | passed down from above. The kbuild Makefile uses information from the | |
39e6e9cf | 92 | .config file to construct various file lists used by kbuild to build |
1da177e4 LT |
93 | any built-in or modular targets. |
94 | ||
95 | scripts/Makefile.* contains all the definitions/rules etc. that | |
96 | are used to build the kernel based on the kbuild makefiles. | |
97 | ||
98 | ||
cd238eff MCC |
99 | 2 Who does what |
100 | =============== | |
1da177e4 LT |
101 | |
102 | People have four different relationships with the kernel Makefiles. | |
103 | ||
104 | *Users* are people who build kernels. These people type commands such as | |
105 | "make menuconfig" or "make". They usually do not read or edit | |
106 | any kernel Makefiles (or any other source files). | |
107 | ||
108 | *Normal developers* are people who work on features such as device | |
109 | drivers, file systems, and network protocols. These people need to | |
a07f6033 | 110 | maintain the kbuild Makefiles for the subsystem they are |
1da177e4 LT |
111 | working on. In order to do this effectively, they need some overall |
112 | knowledge about the kernel Makefiles, plus detailed knowledge about the | |
113 | public interface for kbuild. | |
114 | ||
115 | *Arch developers* are people who work on an entire architecture, such | |
116 | as sparc or ia64. Arch developers need to know about the arch Makefile | |
117 | as well as kbuild Makefiles. | |
118 | ||
119 | *Kbuild developers* are people who work on the kernel build system itself. | |
120 | These people need to know about all aspects of the kernel Makefiles. | |
121 | ||
122 | This document is aimed towards normal developers and arch developers. | |
123 | ||
124 | ||
cd238eff MCC |
125 | 3 The kbuild files |
126 | ================== | |
1da177e4 LT |
127 | |
128 | Most Makefiles within the kernel are kbuild Makefiles that use the | |
a07f6033 | 129 | kbuild infrastructure. This chapter introduces the syntax used in the |
1da177e4 | 130 | kbuild makefiles. |
172c3ae3 | 131 | The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can |
a07f6033 | 132 | be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild' |
172c3ae3 | 133 | file will be used. |
1da177e4 | 134 | |
b26ff488 | 135 | Section 3.1 "Goal definitions" is a quick intro; further chapters provide |
1da177e4 LT |
136 | more details, with real examples. |
137 | ||
cd238eff MCC |
138 | 3.1 Goal definitions |
139 | -------------------- | |
1da177e4 LT |
140 | |
141 | Goal definitions are the main part (heart) of the kbuild Makefile. | |
142 | These lines define the files to be built, any special compilation | |
143 | options, and any subdirectories to be entered recursively. | |
144 | ||
145 | The most simple kbuild makefile contains one line: | |
146 | ||
cd238eff MCC |
147 | Example:: |
148 | ||
1da177e4 LT |
149 | obj-y += foo.o |
150 | ||
5c811e59 | 151 | This tells kbuild that there is one object in that directory, named |
1da177e4 LT |
152 | foo.o. foo.o will be built from foo.c or foo.S. |
153 | ||
154 | If foo.o shall be built as a module, the variable obj-m is used. | |
155 | Therefore the following pattern is often used: | |
156 | ||
cd238eff MCC |
157 | Example:: |
158 | ||
1da177e4 LT |
159 | obj-$(CONFIG_FOO) += foo.o |
160 | ||
161 | $(CONFIG_FOO) evaluates to either y (for built-in) or m (for module). | |
162 | If CONFIG_FOO is neither y nor m, then the file will not be compiled | |
163 | nor linked. | |
164 | ||
cd238eff MCC |
165 | 3.2 Built-in object goals - obj-y |
166 | --------------------------------- | |
1da177e4 LT |
167 | |
168 | The kbuild Makefile specifies object files for vmlinux | |
a07f6033 | 169 | in the $(obj-y) lists. These lists depend on the kernel |
1da177e4 LT |
170 | configuration. |
171 | ||
172 | Kbuild compiles all the $(obj-y) files. It then calls | |
f49821ee | 173 | "$(AR) rcSTP" to merge these files into one built-in.a file. |
dee94953 MY |
174 | This is a thin archive without a symbol table. It will be later |
175 | linked into vmlinux by scripts/link-vmlinux.sh | |
1da177e4 LT |
176 | |
177 | The order of files in $(obj-y) is significant. Duplicates in | |
178 | the lists are allowed: the first instance will be linked into | |
f49821ee | 179 | built-in.a and succeeding instances will be ignored. |
1da177e4 LT |
180 | |
181 | Link order is significant, because certain functions | |
182 | (module_init() / __initcall) will be called during boot in the | |
183 | order they appear. So keep in mind that changing the link | |
a07f6033 JE |
184 | order may e.g. change the order in which your SCSI |
185 | controllers are detected, and thus your disks are renumbered. | |
1da177e4 | 186 | |
cd238eff MCC |
187 | Example:: |
188 | ||
1da177e4 LT |
189 | #drivers/isdn/i4l/Makefile |
190 | # Makefile for the kernel ISDN subsystem and device drivers. | |
191 | # Each configuration option enables a list of files. | |
2f5a2f81 | 192 | obj-$(CONFIG_ISDN_I4L) += isdn.o |
1da177e4 LT |
193 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o |
194 | ||
cd238eff MCC |
195 | 3.3 Loadable module goals - obj-m |
196 | --------------------------------- | |
1da177e4 | 197 | |
39fed701 | 198 | $(obj-m) specifies object files which are built as loadable |
1da177e4 LT |
199 | kernel modules. |
200 | ||
201 | A module may be built from one source file or several source | |
202 | files. In the case of one source file, the kbuild makefile | |
203 | simply adds the file to $(obj-m). | |
204 | ||
cd238eff MCC |
205 | Example:: |
206 | ||
1da177e4 LT |
207 | #drivers/isdn/i4l/Makefile |
208 | obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o | |
209 | ||
210 | Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm' | |
211 | ||
212 | If a kernel module is built from several source files, you specify | |
4f827280 MM |
213 | that you want to build a module in the same way as above; however, |
214 | kbuild needs to know which object files you want to build your | |
215 | module from, so you have to tell it by setting a $(<module_name>-y) | |
216 | variable. | |
1da177e4 | 217 | |
cd238eff MCC |
218 | Example:: |
219 | ||
1da177e4 | 220 | #drivers/isdn/i4l/Makefile |
4f827280 MM |
221 | obj-$(CONFIG_ISDN_I4L) += isdn.o |
222 | isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o | |
1da177e4 LT |
223 | |
224 | In this example, the module name will be isdn.o. Kbuild will | |
4f827280 | 225 | compile the objects listed in $(isdn-y) and then run |
1da177e4 LT |
226 | "$(LD) -r" on the list of these files to generate isdn.o. |
227 | ||
4f827280 | 228 | Due to kbuild recognizing $(<module_name>-y) for composite objects, |
cd238eff | 229 | you can use the value of a `CONFIG_` symbol to optionally include an |
4f827280 | 230 | object file as part of a composite object. |
1da177e4 | 231 | |
cd238eff MCC |
232 | Example:: |
233 | ||
1da177e4 | 234 | #fs/ext2/Makefile |
4f827280 MM |
235 | obj-$(CONFIG_EXT2_FS) += ext2.o |
236 | ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \ | |
237 | namei.o super.o symlink.o | |
238 | ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \ | |
239 | xattr_trusted.o | |
240 | ||
241 | In this example, xattr.o, xattr_user.o and xattr_trusted.o are only | |
242 | part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR) | |
243 | evaluates to 'y'. | |
1da177e4 LT |
244 | |
245 | Note: Of course, when you are building objects into the kernel, | |
246 | the syntax above will also work. So, if you have CONFIG_EXT2_FS=y, | |
247 | kbuild will build an ext2.o file for you out of the individual | |
f49821ee | 248 | parts and then link this into built-in.a, as you would expect. |
1da177e4 | 249 | |
cd238eff MCC |
250 | 3.5 Library file goals - lib-y |
251 | ------------------------------ | |
1da177e4 | 252 | |
a07f6033 | 253 | Objects listed with obj-* are used for modules, or |
f49821ee | 254 | combined in a built-in.a for that specific directory. |
1da177e4 LT |
255 | There is also the possibility to list objects that will |
256 | be included in a library, lib.a. | |
257 | All objects listed with lib-y are combined in a single | |
258 | library for that directory. | |
5d3f083d ML |
259 | Objects that are listed in obj-y and additionally listed in |
260 | lib-y will not be included in the library, since they will | |
261 | be accessible anyway. | |
a07f6033 | 262 | For consistency, objects listed in lib-m will be included in lib.a. |
1da177e4 LT |
263 | |
264 | Note that the same kbuild makefile may list files to be built-in | |
265 | and to be part of a library. Therefore the same directory | |
f49821ee | 266 | may contain both a built-in.a and a lib.a file. |
1da177e4 | 267 | |
cd238eff MCC |
268 | Example:: |
269 | ||
2f5a2f81 MM |
270 | #arch/x86/lib/Makefile |
271 | lib-y := delay.o | |
1da177e4 | 272 | |
2f5a2f81 MM |
273 | This will create a library lib.a based on delay.o. For kbuild to |
274 | actually recognize that there is a lib.a being built, the directory | |
275 | shall be listed in libs-y. | |
cd238eff | 276 | |
23b53061 | 277 | See also "7.4 List directories to visit when descending". |
39e6e9cf | 278 | |
cd238eff | 279 | Use of lib-y is normally restricted to `lib/` and `arch/*/lib`. |
1da177e4 | 280 | |
cd238eff MCC |
281 | 3.6 Descending down in directories |
282 | ---------------------------------- | |
1da177e4 LT |
283 | |
284 | A Makefile is only responsible for building objects in its own | |
285 | directory. Files in subdirectories should be taken care of by | |
286 | Makefiles in these subdirs. The build system will automatically | |
287 | invoke make recursively in subdirectories, provided you let it know of | |
288 | them. | |
289 | ||
a07f6033 | 290 | To do so, obj-y and obj-m are used. |
1da177e4 LT |
291 | ext2 lives in a separate directory, and the Makefile present in fs/ |
292 | tells kbuild to descend down using the following assignment. | |
293 | ||
cd238eff MCC |
294 | Example:: |
295 | ||
1da177e4 LT |
296 | #fs/Makefile |
297 | obj-$(CONFIG_EXT2_FS) += ext2/ | |
298 | ||
299 | If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular) | |
300 | the corresponding obj- variable will be set, and kbuild will descend | |
301 | down in the ext2 directory. | |
28f94a44 MY |
302 | |
303 | Kbuild uses this information not only to decide that it needs to visit | |
304 | the directory, but also to decide whether or not to link objects from | |
305 | the directory into vmlinux. | |
306 | ||
307 | When Kbuild descends into the directory with 'y', all built-in objects | |
308 | from that directory are combined into the built-in.a, which will be | |
309 | eventually linked into vmlinux. | |
310 | ||
311 | When Kbuild descends into the directory with 'm', in contrast, nothing | |
312 | from that directory will be linked into vmlinux. If the Makefile in | |
313 | that directory specifies obj-y, those objects will be left orphan. | |
314 | It is very likely a bug of the Makefile or of dependencies in Kconfig. | |
1da177e4 | 315 | |
c0ea806f MY |
316 | Kbuild also supports dedicated syntax, subdir-y and subdir-m, for |
317 | descending into subdirectories. It is a good fit when you know they | |
318 | do not contain kernel-space objects at all. A typical usage is to let | |
319 | Kbuild descend into subdirectories to build tools. | |
320 | ||
321 | Examples:: | |
322 | ||
323 | # scripts/Makefile | |
324 | subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins | |
325 | subdir-$(CONFIG_MODVERSIONS) += genksyms | |
326 | subdir-$(CONFIG_SECURITY_SELINUX) += selinux | |
327 | ||
328 | Unlike obj-y/m, subdir-y/m does not need the trailing slash since this | |
329 | syntax is always used for directories. | |
330 | ||
cd238eff | 331 | It is good practice to use a `CONFIG_` variable when assigning directory |
1da177e4 | 332 | names. This allows kbuild to totally skip the directory if the |
cd238eff | 333 | corresponding `CONFIG_` option is neither 'y' nor 'm'. |
1da177e4 | 334 | |
d0e628cd MY |
335 | 3.7 Non-builtin vmlinux targets - extra-y |
336 | ----------------------------------------- | |
337 | ||
338 | extra-y specifies targets which are needed for building vmlinux, | |
339 | but not combined into built-in.a. | |
340 | ||
341 | Examples are: | |
342 | ||
343 | 1) head objects | |
344 | ||
345 | Some objects must be placed at the head of vmlinux. They are | |
346 | directly linked to vmlinux without going through built-in.a | |
347 | A typical use-case is an object that contains the entry point. | |
348 | ||
349 | arch/$(SRCARCH)/Makefile should specify such objects as head-y. | |
350 | ||
351 | Discussion: | |
352 | Given that we can control the section order in the linker script, | |
353 | why do we need head-y? | |
354 | ||
355 | 2) vmlinux linker script | |
356 | ||
357 | The linker script for vmlinux is located at | |
358 | arch/$(SRCARCH)/kernel/vmlinux.lds | |
359 | ||
360 | Example:: | |
361 | ||
362 | # arch/x86/kernel/Makefile | |
363 | extra-y := head_$(BITS).o | |
364 | extra-y += head$(BITS).o | |
365 | extra-y += ebda.o | |
366 | extra-y += platform-quirks.o | |
367 | extra-y += vmlinux.lds | |
368 | ||
369 | $(extra-y) should only contain targets needed for vmlinux. | |
370 | ||
371 | Kbuild skips extra-y when vmlinux is apparently not a final goal. | |
372 | (e.g. 'make modules', or building external modules) | |
373 | ||
374 | If you intend to build targets unconditionally, always-y (explained | |
375 | in the next section) is the correct syntax to use. | |
376 | ||
377 | 3.8 Always built goals - always-y | |
378 | --------------------------------- | |
379 | ||
380 | always-y specifies targets which are literally always built when | |
381 | Kbuild visits the Makefile. | |
382 | ||
383 | Example:: | |
384 | # ./Kbuild | |
385 | offsets-file := include/generated/asm-offsets.h | |
386 | always-y += $(offsets-file) | |
387 | ||
388 | 3.9 Compilation flags | |
cd238eff | 389 | --------------------- |
1da177e4 | 390 | |
f77bf014 | 391 | ccflags-y, asflags-y and ldflags-y |
c95940f2 NK |
392 | These three flags apply only to the kbuild makefile in which they |
393 | are assigned. They are used for all the normal cc, as and ld | |
394 | invocations happening during a recursive build. | |
f77bf014 | 395 | Note: Flags with the same behaviour were previously named: |
c95940f2 NK |
396 | EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS. |
397 | They are still supported but their usage is deprecated. | |
1da177e4 | 398 | |
eb07e1b4 | 399 | ccflags-y specifies options for compiling with $(CC). |
1da177e4 | 400 | |
cd238eff MCC |
401 | Example:: |
402 | ||
3d91a353 SD |
403 | # drivers/acpi/acpica/Makefile |
404 | ccflags-y := -Os -D_LINUX -DBUILDING_ACPICA | |
405 | ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT | |
1da177e4 LT |
406 | |
407 | This variable is necessary because the top Makefile owns the | |
a0f97e06 | 408 | variable $(KBUILD_CFLAGS) and uses it for compilation flags for the |
1da177e4 LT |
409 | entire tree. |
410 | ||
5ef87263 | 411 | asflags-y specifies assembler options. |
1da177e4 | 412 | |
cd238eff MCC |
413 | Example:: |
414 | ||
eb07e1b4 MM |
415 | #arch/sparc/kernel/Makefile |
416 | asflags-y := -ansi | |
1da177e4 | 417 | |
eb07e1b4 | 418 | ldflags-y specifies options for linking with $(LD). |
1da177e4 | 419 | |
cd238eff MCC |
420 | Example:: |
421 | ||
eb07e1b4 MM |
422 | #arch/cris/boot/compressed/Makefile |
423 | ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds | |
1da177e4 | 424 | |
720097d8 | 425 | subdir-ccflags-y, subdir-asflags-y |
eb07e1b4 | 426 | The two flags listed above are similar to ccflags-y and asflags-y. |
c95940f2 NK |
427 | The difference is that the subdir- variants have effect for the kbuild |
428 | file where they are present and all subdirectories. | |
429 | Options specified using subdir-* are added to the commandline before | |
430 | the options specified using the non-subdir variants. | |
720097d8 | 431 | |
cd238eff MCC |
432 | Example:: |
433 | ||
720097d8 SR |
434 | subdir-ccflags-y := -Werror |
435 | ||
15d5761a MY |
436 | ccflags-remove-y, asflags-remove-y |
437 | These flags are used to remove particular flags for the compiler, | |
438 | assembler invocations. | |
439 | ||
440 | Example:: | |
441 | ||
442 | ccflags-remove-$(CONFIG_MCOUNT) += -pg | |
443 | ||
1da177e4 | 444 | CFLAGS_$@, AFLAGS_$@ |
1da177e4 LT |
445 | CFLAGS_$@ and AFLAGS_$@ only apply to commands in current |
446 | kbuild makefile. | |
447 | ||
448 | $(CFLAGS_$@) specifies per-file options for $(CC). The $@ | |
449 | part has a literal value which specifies the file that it is for. | |
450 | ||
15d5761a MY |
451 | CFLAGS_$@ has the higher priority than ccflags-remove-y; CFLAGS_$@ |
452 | can re-add compiler flags that were removed by ccflags-remove-y. | |
453 | ||
cd238eff MCC |
454 | Example:: |
455 | ||
1da177e4 LT |
456 | # drivers/scsi/Makefile |
457 | CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF | |
1da177e4 | 458 | |
0653c358 | 459 | This line specify compilation flags for aha152x.o. |
1da177e4 LT |
460 | |
461 | $(AFLAGS_$@) is a similar feature for source files in assembly | |
462 | languages. | |
463 | ||
15d5761a MY |
464 | AFLAGS_$@ has the higher priority than asflags-remove-y; AFLAGS_$@ |
465 | can re-add assembler flags that were removed by asflags-remove-y. | |
466 | ||
cd238eff MCC |
467 | Example:: |
468 | ||
1da177e4 | 469 | # arch/arm/kernel/Makefile |
eb07e1b4 MM |
470 | AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) |
471 | AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312 | |
472 | AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt | |
473 | ||
1da177e4 | 474 | |
d0e628cd MY |
475 | 3.10 Dependency tracking |
476 | ------------------------ | |
1da177e4 LT |
477 | |
478 | Kbuild tracks dependencies on the following: | |
16886949 | 479 | |
cd238eff MCC |
480 | 1) All prerequisite files (both `*.c` and `*.h`) |
481 | 2) `CONFIG_` options used in all prerequisite files | |
1da177e4 LT |
482 | 3) Command-line used to compile target |
483 | ||
484 | Thus, if you change an option to $(CC) all affected files will | |
485 | be re-compiled. | |
486 | ||
d0e628cd MY |
487 | 3.11 Custom Rules |
488 | ----------------- | |
1da177e4 | 489 | |
41cac083 | 490 | Custom rules are used when the kbuild infrastructure does |
1da177e4 LT |
491 | not provide the required support. A typical example is |
492 | header files generated during the build process. | |
5c811e59 | 493 | Another example are the architecture-specific Makefiles which |
41cac083 | 494 | need custom rules to prepare boot images etc. |
1da177e4 | 495 | |
41cac083 | 496 | Custom rules are written as normal Make rules. |
1da177e4 | 497 | Kbuild is not executing in the directory where the Makefile is |
41cac083 | 498 | located, so all custom rules shall use a relative |
1da177e4 LT |
499 | path to prerequisite files and target files. |
500 | ||
41cac083 | 501 | Two variables are used when defining custom rules: |
1da177e4 | 502 | |
cd238eff MCC |
503 | $(src) |
504 | $(src) is a relative path which points to the directory | |
505 | where the Makefile is located. Always use $(src) when | |
506 | referring to files located in the src tree. | |
507 | ||
508 | $(obj) | |
509 | $(obj) is a relative path which points to the directory | |
510 | where the target is saved. Always use $(obj) when | |
511 | referring to generated files. | |
1da177e4 | 512 | |
cd238eff | 513 | Example:: |
1da177e4 | 514 | |
1da177e4 LT |
515 | #drivers/scsi/Makefile |
516 | $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl | |
517 | $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl | |
518 | ||
41cac083 | 519 | This is a custom rule, following the normal syntax |
cd238eff MCC |
520 | required by make. |
521 | ||
522 | The target file depends on two prerequisite files. References | |
523 | to the target file are prefixed with $(obj), references | |
524 | to prerequisites are referenced with $(src) (because they are not | |
525 | generated files). | |
526 | ||
527 | $(kecho) | |
528 | echoing information to user in a rule is often a good practice | |
529 | but when execution "make -s" one does not expect to see any output | |
530 | except for warnings/errors. | |
531 | To support this kbuild defines $(kecho) which will echo out the | |
532 | text following $(kecho) to stdout except if "make -s" is used. | |
533 | ||
534 | Example:: | |
535 | ||
41cac083 MY |
536 | # arch/arm/Makefile |
537 | $(BOOT_TARGETS): vmlinux | |
538 | $(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) $(boot)/$@ | |
539 | @$(kecho) ' Kernel: $(boot)/$@ is ready' | |
5410ecc0 | 540 | |
41cac083 MY |
541 | When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand |
542 | of a command is normally displayed. | |
543 | To enable this behaviour for custom commands kbuild requires | |
544 | two variables to be set:: | |
545 | ||
546 | quiet_cmd_<command> - what shall be echoed | |
547 | cmd_<command> - the command to execute | |
548 | ||
549 | Example:: | |
550 | ||
551 | # lib/Makefile | |
552 | quiet_cmd_crc32 = GEN $@ | |
553 | cmd_crc32 = $< > $@ | |
554 | ||
555 | $(obj)/crc32table.h: $(obj)/gen_crc32table | |
556 | $(call cmd,crc32) | |
557 | ||
558 | When updating the $(obj)/crc32table.h target, the line: | |
559 | ||
560 | GEN lib/crc32table.h | |
561 | ||
562 | will be displayed with "make KBUILD_VERBOSE=0". | |
5410ecc0 | 563 | |
d0e628cd | 564 | 3.12 Command change detection |
39bb232a MY |
565 | ----------------------------- |
566 | ||
567 | When the rule is evaluated, timestamps are compared between the target | |
568 | and its prerequisite files. GNU Make updates the target when any of the | |
569 | prerequisites is newer than that. | |
570 | ||
571 | The target should be rebuilt also when the command line has changed | |
572 | since the last invocation. This is not supported by Make itself, so | |
573 | Kbuild achieves this by a kind of meta-programming. | |
574 | ||
575 | if_changed is the macro used for this purpose, in the following form:: | |
576 | ||
577 | quiet_cmd_<command> = ... | |
578 | cmd_<command> = ... | |
579 | ||
580 | <target>: <source(s)> FORCE | |
581 | $(call if_changed,<command>) | |
582 | ||
583 | Any target that utilizes if_changed must be listed in $(targets), | |
584 | otherwise the command line check will fail, and the target will | |
585 | always be built. | |
586 | ||
587 | If the target is already listed in the recognized syntax such as | |
588 | obj-y/m, lib-y/m, extra-y/m, always-y/m, hostprogs, userprogs, Kbuild | |
589 | automatically adds it to $(targets). Otherwise, the target must be | |
590 | explicitly added to $(targets). | |
591 | ||
592 | Assignments to $(targets) are without $(obj)/ prefix. if_changed may be | |
5625dcfb | 593 | used in conjunction with custom rules as defined in "3.11 Custom Rules". |
39bb232a MY |
594 | |
595 | Note: It is a typical mistake to forget the FORCE prerequisite. | |
596 | Another common pitfall is that whitespace is sometimes significant; for | |
597 | instance, the below will fail (note the extra space after the comma):: | |
598 | ||
599 | target: source(s) FORCE | |
600 | ||
601 | **WRONG!** $(call if_changed, objcopy) | |
602 | ||
603 | Note: | |
604 | if_changed should not be used more than once per target. | |
605 | It stores the executed command in a corresponding .cmd | |
606 | file and multiple calls would result in overwrites and | |
607 | unwanted results when the target is up to date and only the | |
608 | tests on changed commands trigger execution of commands. | |
609 | ||
d0e628cd | 610 | 3.13 $(CC) support functions |
cd238eff | 611 | ---------------------------- |
20a468b5 | 612 | |
a07f6033 | 613 | The kernel may be built with several different versions of |
20a468b5 | 614 | $(CC), each supporting a unique set of features and options. |
39fed701 | 615 | kbuild provides basic support to check for valid options for $(CC). |
e95be9a5 | 616 | $(CC) is usually the gcc compiler, but other alternatives are |
20a468b5 SR |
617 | available. |
618 | ||
619 | as-option | |
a07f6033 | 620 | as-option is used to check if $(CC) -- when used to compile |
cd238eff | 621 | assembler (`*.S`) files -- supports the given option. An optional |
a07f6033 | 622 | second option may be specified if the first option is not supported. |
20a468b5 | 623 | |
cd238eff MCC |
624 | Example:: |
625 | ||
20a468b5 SR |
626 | #arch/sh/Makefile |
627 | cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),) | |
628 | ||
a07f6033 | 629 | In the above example, cflags-y will be assigned the option |
20a468b5 SR |
630 | -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC). |
631 | The second argument is optional, and if supplied will be used | |
cd238eff MCC |
632 | if first argument is not supported. |
633 | ||
e2414910 AK |
634 | as-instr |
635 | as-instr checks if the assembler reports a specific instruction | |
636 | and then outputs either option1 or option2 | |
637 | C escapes are supported in the test instruction | |
5ef87263 | 638 | Note: as-instr-option uses KBUILD_AFLAGS for assembler options |
e2414910 | 639 | |
20a468b5 | 640 | cc-option |
39fed701 GU |
641 | cc-option is used to check if $(CC) supports a given option, and if |
642 | not supported to use an optional second option. | |
20a468b5 | 643 | |
cd238eff MCC |
644 | Example:: |
645 | ||
25eb650a | 646 | #arch/x86/Makefile |
20a468b5 SR |
647 | cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) |
648 | ||
5c811e59 | 649 | In the above example, cflags-y will be assigned the option |
a07f6033 JE |
650 | -march=pentium-mmx if supported by $(CC), otherwise -march=i586. |
651 | The second argument to cc-option is optional, and if omitted, | |
20a468b5 | 652 | cflags-y will be assigned no value if first option is not supported. |
a0f97e06 | 653 | Note: cc-option uses KBUILD_CFLAGS for $(CC) options |
20a468b5 SR |
654 | |
655 | cc-option-yn | |
39e6e9cf | 656 | cc-option-yn is used to check if gcc supports a given option |
20a468b5 SR |
657 | and return 'y' if supported, otherwise 'n'. |
658 | ||
cd238eff MCC |
659 | Example:: |
660 | ||
20a468b5 SR |
661 | #arch/ppc/Makefile |
662 | biarch := $(call cc-option-yn, -m32) | |
663 | aflags-$(biarch) += -a32 | |
664 | cflags-$(biarch) += -m32 | |
39e6e9cf | 665 | |
a07f6033 JE |
666 | In the above example, $(biarch) is set to y if $(CC) supports the -m32 |
667 | option. When $(biarch) equals 'y', the expanded variables $(aflags-y) | |
668 | and $(cflags-y) will be assigned the values -a32 and -m32, | |
669 | respectively. | |
a0f97e06 | 670 | Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options |
20a468b5 | 671 | |
8417da6f MM |
672 | cc-disable-warning |
673 | cc-disable-warning checks if gcc supports a given warning and returns | |
674 | the commandline switch to disable it. This special function is needed, | |
675 | because gcc 4.4 and later accept any unknown -Wno-* option and only | |
676 | warn about it if there is another warning in the source file. | |
677 | ||
cd238eff MCC |
678 | Example:: |
679 | ||
8417da6f MM |
680 | KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) |
681 | ||
682 | In the above example, -Wno-unused-but-set-variable will be added to | |
683 | KBUILD_CFLAGS only if gcc really accepts it. | |
684 | ||
20a468b5 | 685 | cc-ifversion |
6dcb4e5e MY |
686 | cc-ifversion tests the version of $(CC) and equals the fourth parameter |
687 | if version expression is true, or the fifth (if given) if the version | |
688 | expression is false. | |
20a468b5 | 689 | |
cd238eff MCC |
690 | Example:: |
691 | ||
20a468b5 | 692 | #fs/reiserfs/Makefile |
f77bf014 | 693 | ccflags-y := $(call cc-ifversion, -lt, 0402, -O1) |
20a468b5 | 694 | |
f77bf014 | 695 | In this example, ccflags-y will be assigned the value -O1 if the |
20a468b5 | 696 | $(CC) version is less than 4.2. |
39e6e9cf | 697 | cc-ifversion takes all the shell operators: |
20a468b5 SR |
698 | -eq, -ne, -lt, -le, -gt, and -ge |
699 | The third parameter may be a text as in this example, but it may also | |
700 | be an expanded variable or a macro. | |
701 | ||
910b4046 | 702 | cc-cross-prefix |
631bcfbb | 703 | cc-cross-prefix is used to check if there exists a $(CC) in path with |
910b4046 SR |
704 | one of the listed prefixes. The first prefix where there exist a |
705 | prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found | |
706 | then nothing is returned. | |
707 | Additional prefixes are separated by a single space in the | |
708 | call of cc-cross-prefix. | |
631bcfbb GU |
709 | This functionality is useful for architecture Makefiles that try |
710 | to set CROSS_COMPILE to well-known values but may have several | |
910b4046 | 711 | values to select between. |
631bcfbb GU |
712 | It is recommended only to try to set CROSS_COMPILE if it is a cross |
713 | build (host arch is different from target arch). And if CROSS_COMPILE | |
910b4046 SR |
714 | is already set then leave it with the old value. |
715 | ||
cd238eff MCC |
716 | Example:: |
717 | ||
910b4046 SR |
718 | #arch/m68k/Makefile |
719 | ifneq ($(SUBARCH),$(ARCH)) | |
720 | ifeq ($(CROSS_COMPILE),) | |
721 | CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-) | |
722 | endif | |
723 | endif | |
724 | ||
d0e628cd | 725 | 3.14 $(LD) support functions |
cd238eff | 726 | ---------------------------- |
691ef3e7 SR |
727 | |
728 | ld-option | |
729 | ld-option is used to check if $(LD) supports the supplied option. | |
730 | ld-option takes two options as arguments. | |
731 | The second argument is an optional option that can be used if the | |
732 | first option is not supported by $(LD). | |
733 | ||
cd238eff MCC |
734 | Example:: |
735 | ||
691ef3e7 | 736 | #Makefile |
5b83df2b | 737 | LDFLAGS_vmlinux += $(call ld-option, -X) |
691ef3e7 | 738 | |
d0e628cd | 739 | 3.15 Script invocation |
eb38f37c LB |
740 | ---------------------- |
741 | ||
742 | Make rules may invoke scripts to build the kernel. The rules shall | |
743 | always provide the appropriate interpreter to execute the script. They | |
744 | shall not rely on the execute bits being set, and shall not invoke the | |
745 | script directly. For the convenience of manual script invocation, such | |
746 | as invoking ./scripts/checkpatch.pl, it is recommended to set execute | |
747 | bits on the scripts nonetheless. | |
748 | ||
749 | Kbuild provides variables $(CONFIG_SHELL), $(AWK), $(PERL), | |
d8d2d382 | 750 | and $(PYTHON3) to refer to interpreters for the respective |
eb38f37c LB |
751 | scripts. |
752 | ||
753 | Example:: | |
754 | ||
755 | #Makefile | |
756 | cmd_depmod = $(CONFIG_SHELL) $(srctree)/scripts/depmod.sh $(DEPMOD) \ | |
757 | $(KERNELRELEASE) | |
691ef3e7 | 758 | |
cd238eff MCC |
759 | 4 Host Program support |
760 | ====================== | |
1da177e4 LT |
761 | |
762 | Kbuild supports building executables on the host for use during the | |
763 | compilation stage. | |
764 | Two steps are required in order to use a host executable. | |
765 | ||
766 | The first step is to tell kbuild that a host program exists. This is | |
5f2fb52f | 767 | done utilising the variable "hostprogs". |
1da177e4 LT |
768 | |
769 | The second step is to add an explicit dependency to the executable. | |
39e6e9cf | 770 | This can be done in two ways. Either add the dependency in a rule, |
5f2fb52f | 771 | or utilise the variable "always-y". |
1da177e4 LT |
772 | Both possibilities are described in the following. |
773 | ||
cd238eff MCC |
774 | 4.1 Simple Host Program |
775 | ----------------------- | |
1da177e4 LT |
776 | |
777 | In some cases there is a need to compile and run a program on the | |
778 | computer where the build is running. | |
779 | The following line tells kbuild that the program bin2hex shall be | |
780 | built on the build host. | |
781 | ||
cd238eff MCC |
782 | Example:: |
783 | ||
5f2fb52f | 784 | hostprogs := bin2hex |
1da177e4 LT |
785 | |
786 | Kbuild assumes in the above example that bin2hex is made from a single | |
787 | c-source file named bin2hex.c located in the same directory as | |
788 | the Makefile. | |
39e6e9cf | 789 | |
cd238eff MCC |
790 | 4.2 Composite Host Programs |
791 | --------------------------- | |
1da177e4 LT |
792 | |
793 | Host programs can be made up based on composite objects. | |
794 | The syntax used to define composite objects for host programs is | |
795 | similar to the syntax used for kernel objects. | |
5d3f083d | 796 | $(<executable>-objs) lists all objects used to link the final |
1da177e4 LT |
797 | executable. |
798 | ||
cd238eff MCC |
799 | Example:: |
800 | ||
1da177e4 | 801 | #scripts/lxdialog/Makefile |
5f2fb52f | 802 | hostprogs := lxdialog |
1da177e4 LT |
803 | lxdialog-objs := checklist.o lxdialog.o |
804 | ||
805 | Objects with extension .o are compiled from the corresponding .c | |
a07f6033 | 806 | files. In the above example, checklist.c is compiled to checklist.o |
1da177e4 | 807 | and lxdialog.c is compiled to lxdialog.o. |
cd238eff | 808 | |
a07f6033 | 809 | Finally, the two .o files are linked to the executable, lxdialog. |
1da177e4 LT |
810 | Note: The syntax <executable>-y is not permitted for host-programs. |
811 | ||
cd238eff MCC |
812 | 4.3 Using C++ for host programs |
813 | ------------------------------- | |
1da177e4 LT |
814 | |
815 | kbuild offers support for host programs written in C++. This was | |
816 | introduced solely to support kconfig, and is not recommended | |
817 | for general use. | |
818 | ||
cd238eff MCC |
819 | Example:: |
820 | ||
1da177e4 | 821 | #scripts/kconfig/Makefile |
5f2fb52f | 822 | hostprogs := qconf |
1da177e4 LT |
823 | qconf-cxxobjs := qconf.o |
824 | ||
825 | In the example above the executable is composed of the C++ file | |
826 | qconf.cc - identified by $(qconf-cxxobjs). | |
39e6e9cf | 827 | |
39fed701 | 828 | If qconf is composed of a mixture of .c and .cc files, then an |
1da177e4 LT |
829 | additional line can be used to identify this. |
830 | ||
cd238eff MCC |
831 | Example:: |
832 | ||
1da177e4 | 833 | #scripts/kconfig/Makefile |
5f2fb52f | 834 | hostprogs := qconf |
1da177e4 LT |
835 | qconf-cxxobjs := qconf.o |
836 | qconf-objs := check.o | |
39e6e9cf | 837 | |
cd238eff MCC |
838 | 4.4 Controlling compiler options for host programs |
839 | -------------------------------------------------- | |
1da177e4 LT |
840 | |
841 | When compiling host programs, it is possible to set specific flags. | |
842 | The programs will always be compiled utilising $(HOSTCC) passed | |
96f14fe7 | 843 | the options specified in $(KBUILD_HOSTCFLAGS). |
1da177e4 | 844 | To set flags that will take effect for all host programs created |
a07f6033 | 845 | in that Makefile, use the variable HOST_EXTRACFLAGS. |
1da177e4 | 846 | |
cd238eff MCC |
847 | Example:: |
848 | ||
1da177e4 LT |
849 | #scripts/lxdialog/Makefile |
850 | HOST_EXTRACFLAGS += -I/usr/include/ncurses | |
39e6e9cf | 851 | |
1da177e4 LT |
852 | To set specific flags for a single file the following construction |
853 | is used: | |
854 | ||
cd238eff MCC |
855 | Example:: |
856 | ||
1da177e4 LT |
857 | #arch/ppc64/boot/Makefile |
858 | HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE) | |
39e6e9cf | 859 | |
1da177e4 | 860 | It is also possible to specify additional options to the linker. |
39e6e9cf | 861 | |
cd238eff MCC |
862 | Example:: |
863 | ||
1da177e4 | 864 | #scripts/kconfig/Makefile |
c86b1f93 | 865 | HOSTLDLIBS_qconf := -L$(QTDIR)/lib |
1da177e4 | 866 | |
a07f6033 JE |
867 | When linking qconf, it will be passed the extra option |
868 | "-L$(QTDIR)/lib". | |
39e6e9cf | 869 | |
cd238eff MCC |
870 | 4.5 When host programs are actually built |
871 | ----------------------------------------- | |
1da177e4 LT |
872 | |
873 | Kbuild will only build host-programs when they are referenced | |
874 | as a prerequisite. | |
875 | This is possible in two ways: | |
876 | ||
41cac083 | 877 | (1) List the prerequisite explicitly in a custom rule. |
1da177e4 | 878 | |
cd238eff MCC |
879 | Example:: |
880 | ||
1da177e4 | 881 | #drivers/pci/Makefile |
5f2fb52f | 882 | hostprogs := gen-devlist |
1da177e4 LT |
883 | $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist |
884 | ( cd $(obj); ./gen-devlist ) < $< | |
885 | ||
39e6e9cf | 886 | The target $(obj)/devlist.h will not be built before |
1da177e4 | 887 | $(obj)/gen-devlist is updated. Note that references to |
41cac083 | 888 | the host programs in custom rules must be prefixed with $(obj). |
1da177e4 | 889 | |
5f2fb52f | 890 | (2) Use always-y |
cd238eff | 891 | |
41cac083 | 892 | When there is no suitable custom rule, and the host program |
5f2fb52f | 893 | shall be built when a makefile is entered, the always-y |
1da177e4 LT |
894 | variable shall be used. |
895 | ||
cd238eff MCC |
896 | Example:: |
897 | ||
1da177e4 | 898 | #scripts/lxdialog/Makefile |
5f2fb52f MY |
899 | hostprogs := lxdialog |
900 | always-y := $(hostprogs) | |
1da177e4 | 901 | |
faabed29 MY |
902 | Kbuild provides the following shorthand for this: |
903 | ||
904 | hostprogs-always-y := lxdialog | |
905 | ||
1da177e4 LT |
906 | This will tell kbuild to build lxdialog even if not referenced in |
907 | any rule. | |
908 | ||
e079a08c MY |
909 | 5 Userspace Program support |
910 | =========================== | |
911 | ||
912 | Just like host programs, Kbuild also supports building userspace executables | |
913 | for the target architecture (i.e. the same architecture as you are building | |
914 | the kernel for). | |
915 | ||
916 | The syntax is quite similar. The difference is to use "userprogs" instead of | |
917 | "hostprogs". | |
918 | ||
919 | 5.1 Simple Userspace Program | |
920 | ---------------------------- | |
921 | ||
922 | The following line tells kbuild that the program bpf-direct shall be | |
923 | built for the target architecture. | |
924 | ||
925 | Example:: | |
926 | ||
927 | userprogs := bpf-direct | |
928 | ||
929 | Kbuild assumes in the above example that bpf-direct is made from a | |
930 | single C source file named bpf-direct.c located in the same directory | |
931 | as the Makefile. | |
932 | ||
933 | 5.2 Composite Userspace Programs | |
934 | -------------------------------- | |
935 | ||
936 | Userspace programs can be made up based on composite objects. | |
937 | The syntax used to define composite objects for userspace programs is | |
938 | similar to the syntax used for kernel objects. | |
939 | $(<executable>-objs) lists all objects used to link the final | |
940 | executable. | |
941 | ||
942 | Example:: | |
943 | ||
944 | #samples/seccomp/Makefile | |
945 | userprogs := bpf-fancy | |
946 | bpf-fancy-objs := bpf-fancy.o bpf-helper.o | |
947 | ||
948 | Objects with extension .o are compiled from the corresponding .c | |
949 | files. In the above example, bpf-fancy.c is compiled to bpf-fancy.o | |
950 | and bpf-helper.c is compiled to bpf-helper.o. | |
951 | ||
952 | Finally, the two .o files are linked to the executable, bpf-fancy. | |
953 | Note: The syntax <executable>-y is not permitted for userspace programs. | |
954 | ||
955 | 5.3 Controlling compiler options for userspace programs | |
956 | ------------------------------------------------------- | |
957 | ||
958 | When compiling userspace programs, it is possible to set specific flags. | |
959 | The programs will always be compiled utilising $(CC) passed | |
960 | the options specified in $(KBUILD_USERCFLAGS). | |
961 | To set flags that will take effect for all userspace programs created | |
962 | in that Makefile, use the variable userccflags. | |
963 | ||
964 | Example:: | |
965 | ||
966 | # samples/seccomp/Makefile | |
967 | userccflags += -I usr/include | |
968 | ||
969 | To set specific flags for a single file the following construction | |
970 | is used: | |
971 | ||
972 | Example:: | |
973 | ||
974 | bpf-helper-userccflags += -I user/include | |
975 | ||
976 | It is also possible to specify additional options to the linker. | |
977 | ||
978 | Example:: | |
979 | ||
980 | # net/bpfilter/Makefile | |
981 | bpfilter_umh-userldflags += -static | |
982 | ||
983 | When linking bpfilter_umh, it will be passed the extra option -static. | |
984 | ||
f67695c9 EB |
985 | From command line, :ref:`USERCFLAGS and USERLDFLAGS <userkbuildflags>` will also be used. |
986 | ||
e079a08c MY |
987 | 5.4 When userspace programs are actually built |
988 | ---------------------------------------------- | |
989 | ||
faabed29 MY |
990 | Kbuild builds userspace programs only when told to do so. |
991 | There are two ways to do this. | |
992 | ||
993 | (1) Add it as the prerequisite of another file | |
994 | ||
995 | Example:: | |
996 | ||
997 | #net/bpfilter/Makefile | |
998 | userprogs := bpfilter_umh | |
999 | $(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh | |
1000 | ||
1001 | $(obj)/bpfilter_umh is built before $(obj)/bpfilter_umh_blob.o | |
1002 | ||
1003 | (2) Use always-y | |
1004 | ||
1005 | Example:: | |
1006 | ||
1007 | userprogs := binderfs_example | |
1008 | always-y := $(userprogs) | |
1009 | ||
1010 | Kbuild provides the following shorthand for this: | |
1011 | ||
1012 | userprogs-always-y := binderfs_example | |
1013 | ||
1014 | This will tell Kbuild to build binderfs_example when it visits this | |
1015 | Makefile. | |
e079a08c MY |
1016 | |
1017 | 6 Kbuild clean infrastructure | |
cd238eff | 1018 | ============================= |
1da177e4 | 1019 | |
a07f6033 | 1020 | "make clean" deletes most generated files in the obj tree where the kernel |
1da177e4 | 1021 | is compiled. This includes generated files such as host programs. |
5f2fb52f MY |
1022 | Kbuild knows targets listed in $(hostprogs), $(always-y), $(always-m), |
1023 | $(always-), $(extra-y), $(extra-) and $(targets). They are all deleted | |
1024 | during "make clean". Files matching the patterns "*.[oas]", "*.ko", plus | |
1025 | some additional files generated by kbuild are deleted all over the kernel | |
1026 | source tree when "make clean" is executed. | |
1da177e4 | 1027 | |
1634f2bf MY |
1028 | Additional files or directories can be specified in kbuild makefiles by use of |
1029 | $(clean-files). | |
1da177e4 | 1030 | |
cd238eff MCC |
1031 | Example:: |
1032 | ||
97659181 MM |
1033 | #lib/Makefile |
1034 | clean-files := crc32table.h | |
1da177e4 | 1035 | |
bd55daf4 JR |
1036 | When executing "make clean", the file "crc32table.h" will be deleted. |
1037 | Kbuild will assume files to be in the same relative directory as the | |
97659181 | 1038 | Makefile, except if prefixed with $(objtree). |
1da177e4 | 1039 | |
1634f2bf MY |
1040 | To exclude certain files or directories from make clean, use the |
1041 | $(no-clean-files) variable. | |
ef8ff89b | 1042 | |
1da177e4 LT |
1043 | Usually kbuild descends down in subdirectories due to "obj-* := dir/", |
1044 | but in the architecture makefiles where the kbuild infrastructure | |
1045 | is not sufficient this sometimes needs to be explicit. | |
1046 | ||
cd238eff MCC |
1047 | Example:: |
1048 | ||
25eb650a | 1049 | #arch/x86/boot/Makefile |
eabc8bcb | 1050 | subdir- := compressed |
1da177e4 LT |
1051 | |
1052 | The above assignment instructs kbuild to descend down in the | |
1053 | directory compressed/ when "make clean" is executed. | |
1054 | ||
8c4d9b14 | 1055 | Note 1: arch/$(SRCARCH)/Makefile cannot use "subdir-", because that file is |
8212f898 MY |
1056 | included in the top level makefile. Instead, arch/$(SRCARCH)/Kbuild can use |
1057 | "subdir-". | |
1da177e4 LT |
1058 | |
1059 | Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will | |
1060 | be visited during "make clean". | |
1061 | ||
e079a08c | 1062 | 7 Architecture Makefiles |
cd238eff | 1063 | ======================== |
1da177e4 LT |
1064 | |
1065 | The top level Makefile sets up the environment and does the preparation, | |
1066 | before starting to descend down in the individual directories. | |
a07f6033 | 1067 | The top level makefile contains the generic part, whereas |
8c4d9b14 | 1068 | arch/$(SRCARCH)/Makefile contains what is required to set up kbuild |
a07f6033 | 1069 | for said architecture. |
8c4d9b14 | 1070 | To do so, arch/$(SRCARCH)/Makefile sets up a number of variables and defines |
1da177e4 LT |
1071 | a few targets. |
1072 | ||
a07f6033 | 1073 | When kbuild executes, the following steps are followed (roughly): |
cd238eff | 1074 | |
a07f6033 | 1075 | 1) Configuration of the kernel => produce .config |
1da177e4 | 1076 | 2) Store kernel version in include/linux/version.h |
b22ae40e | 1077 | 3) Updating all other prerequisites to the target prepare: |
8c4d9b14 | 1078 | - Additional prerequisites are specified in arch/$(SRCARCH)/Makefile |
b22ae40e | 1079 | 4) Recursively descend down in all directories listed in |
1da177e4 | 1080 | init-* core* drivers-* net-* libs-* and build all targets. |
8c4d9b14 | 1081 | - The values of the above variables are expanded in arch/$(SRCARCH)/Makefile. |
b22ae40e | 1082 | 5) All object files are then linked and the resulting file vmlinux is |
a07f6033 | 1083 | located at the root of the obj tree. |
1da177e4 | 1084 | The very first objects linked are listed in head-y, assigned by |
8c4d9b14 | 1085 | arch/$(SRCARCH)/Makefile. |
b22ae40e | 1086 | 6) Finally, the architecture-specific part does any required post processing |
1da177e4 LT |
1087 | and builds the final bootimage. |
1088 | - This includes building boot records | |
5c811e59 | 1089 | - Preparing initrd images and the like |
1da177e4 LT |
1090 | |
1091 | ||
e079a08c | 1092 | 7.1 Set variables to tweak the build to the architecture |
cd238eff | 1093 | -------------------------------------------------------- |
1da177e4 | 1094 | |
c0901577 | 1095 | KBUILD_LDFLAGS |
cd238eff | 1096 | Generic $(LD) options |
1da177e4 LT |
1097 | |
1098 | Flags used for all invocations of the linker. | |
1099 | Often specifying the emulation is sufficient. | |
1100 | ||
cd238eff MCC |
1101 | Example:: |
1102 | ||
1da177e4 | 1103 | #arch/s390/Makefile |
c0901577 | 1104 | KBUILD_LDFLAGS := -m elf_s390 |
cd238eff | 1105 | |
f77bf014 | 1106 | Note: ldflags-y can be used to further customise |
b26ff488 | 1107 | the flags used. See section 3.7. |
39e6e9cf | 1108 | |
cd238eff MCC |
1109 | LDFLAGS_vmlinux |
1110 | Options for $(LD) when linking vmlinux | |
1da177e4 LT |
1111 | |
1112 | LDFLAGS_vmlinux is used to specify additional flags to pass to | |
a07f6033 | 1113 | the linker when linking the final vmlinux image. |
1da177e4 LT |
1114 | LDFLAGS_vmlinux uses the LDFLAGS_$@ support. |
1115 | ||
cd238eff MCC |
1116 | Example:: |
1117 | ||
25eb650a | 1118 | #arch/x86/Makefile |
1da177e4 LT |
1119 | LDFLAGS_vmlinux := -e stext |
1120 | ||
cd238eff MCC |
1121 | OBJCOPYFLAGS |
1122 | objcopy flags | |
1da177e4 LT |
1123 | |
1124 | When $(call if_changed,objcopy) is used to translate a .o file, | |
a07f6033 | 1125 | the flags specified in OBJCOPYFLAGS will be used. |
1da177e4 LT |
1126 | $(call if_changed,objcopy) is often used to generate raw binaries on |
1127 | vmlinux. | |
1128 | ||
cd238eff MCC |
1129 | Example:: |
1130 | ||
1da177e4 LT |
1131 | #arch/s390/Makefile |
1132 | OBJCOPYFLAGS := -O binary | |
1133 | ||
1134 | #arch/s390/boot/Makefile | |
1135 | $(obj)/image: vmlinux FORCE | |
1136 | $(call if_changed,objcopy) | |
1137 | ||
a07f6033 | 1138 | In this example, the binary $(obj)/image is a binary version of |
1da177e4 LT |
1139 | vmlinux. The usage of $(call if_changed,xxx) will be described later. |
1140 | ||
cd238eff | 1141 | KBUILD_AFLAGS |
5ef87263 | 1142 | Assembler flags |
1da177e4 LT |
1143 | |
1144 | Default value - see top level Makefile | |
1145 | Append or modify as required per architecture. | |
1146 | ||
cd238eff MCC |
1147 | Example:: |
1148 | ||
1da177e4 | 1149 | #arch/sparc64/Makefile |
222d394d | 1150 | KBUILD_AFLAGS += -m64 -mcpu=ultrasparc |
1da177e4 | 1151 | |
cd238eff MCC |
1152 | KBUILD_CFLAGS |
1153 | $(CC) compiler flags | |
1da177e4 LT |
1154 | |
1155 | Default value - see top level Makefile | |
1156 | Append or modify as required per architecture. | |
1157 | ||
a0f97e06 | 1158 | Often, the KBUILD_CFLAGS variable depends on the configuration. |
1da177e4 | 1159 | |
cd238eff MCC |
1160 | Example:: |
1161 | ||
ff4eb04c PB |
1162 | #arch/x86/boot/compressed/Makefile |
1163 | cflags-$(CONFIG_X86_32) := -march=i386 | |
1164 | cflags-$(CONFIG_X86_64) := -mcmodel=small | |
a0f97e06 | 1165 | KBUILD_CFLAGS += $(cflags-y) |
1da177e4 LT |
1166 | |
1167 | Many arch Makefiles dynamically run the target C compiler to | |
cd238eff | 1168 | probe supported options:: |
1da177e4 | 1169 | |
25eb650a | 1170 | #arch/x86/Makefile |
1da177e4 LT |
1171 | |
1172 | ... | |
1173 | cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ | |
1174 | -march=pentium2,-march=i686) | |
1175 | ... | |
1176 | # Disable unit-at-a-time mode ... | |
a0f97e06 | 1177 | KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time) |
1da177e4 LT |
1178 | ... |
1179 | ||
1180 | ||
a07f6033 | 1181 | The first example utilises the trick that a config option expands |
1da177e4 LT |
1182 | to 'y' when selected. |
1183 | ||
cd238eff | 1184 | KBUILD_AFLAGS_KERNEL |
5ef87263 | 1185 | Assembler options specific for built-in |
1da177e4 | 1186 | |
80c00ba9 | 1187 | $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile |
1da177e4 LT |
1188 | resident kernel code. |
1189 | ||
cd238eff | 1190 | KBUILD_AFLAGS_MODULE |
5ef87263 | 1191 | Assembler options specific for modules |
1da177e4 | 1192 | |
39fed701 | 1193 | $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that |
5ef87263 | 1194 | are used for assembler. |
cd238eff | 1195 | |
2eebb7ab | 1196 | From commandline AFLAGS_MODULE shall be used (see kbuild.rst). |
1da177e4 | 1197 | |
cd238eff MCC |
1198 | KBUILD_CFLAGS_KERNEL |
1199 | $(CC) options specific for built-in | |
80c00ba9 SR |
1200 | |
1201 | $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile | |
1202 | resident kernel code. | |
1203 | ||
cd238eff MCC |
1204 | KBUILD_CFLAGS_MODULE |
1205 | Options for $(CC) when building modules | |
6588169d | 1206 | |
39fed701 | 1207 | $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that |
6588169d | 1208 | are used for $(CC). |
2eebb7ab | 1209 | From commandline CFLAGS_MODULE shall be used (see kbuild.rst). |
6588169d | 1210 | |
cd238eff MCC |
1211 | KBUILD_LDFLAGS_MODULE |
1212 | Options for $(LD) when linking modules | |
6588169d | 1213 | |
39fed701 | 1214 | $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options |
6588169d | 1215 | used when linking modules. This is often a linker script. |
cd238eff | 1216 | |
2eebb7ab | 1217 | From commandline LDFLAGS_MODULE shall be used (see kbuild.rst). |
39e6e9cf | 1218 | |
888f0c34 MY |
1219 | KBUILD_LDS |
1220 | ||
1221 | The linker script with full path. Assigned by the top-level Makefile. | |
1222 | ||
10df0638 MY |
1223 | KBUILD_LDS_MODULE |
1224 | ||
1225 | The module linker script with full path. Assigned by the top-level | |
1226 | Makefile and additionally by the arch Makefile. | |
1227 | ||
888f0c34 MY |
1228 | KBUILD_VMLINUX_OBJS |
1229 | ||
1230 | All object files for vmlinux. They are linked to vmlinux in the same | |
1231 | order as listed in KBUILD_VMLINUX_OBJS. | |
1232 | ||
1233 | KBUILD_VMLINUX_LIBS | |
1234 | ||
1235 | All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and | |
1236 | KBUILD_VMLINUX_LIBS together specify all the object files used to | |
1237 | link vmlinux. | |
61754c18 | 1238 | |
e079a08c | 1239 | 7.2 Add prerequisites to archheaders |
cd238eff | 1240 | ------------------------------------ |
052ad274 PA |
1241 | |
1242 | The archheaders: rule is used to generate header files that | |
f3c8d4c7 | 1243 | may be installed into user space by "make header_install". |
052ad274 PA |
1244 | |
1245 | It is run before "make archprepare" when run on the | |
1246 | architecture itself. | |
1247 | ||
1248 | ||
e079a08c | 1249 | 7.3 Add prerequisites to archprepare |
cd238eff | 1250 | ------------------------------------ |
1da177e4 | 1251 | |
a07f6033 | 1252 | The archprepare: rule is used to list prerequisites that need to be |
1da177e4 | 1253 | built before starting to descend down in the subdirectories. |
a07f6033 | 1254 | This is usually used for header files containing assembler constants. |
1da177e4 | 1255 | |
cd238eff MCC |
1256 | Example:: |
1257 | ||
5bb78269 SR |
1258 | #arch/arm/Makefile |
1259 | archprepare: maketools | |
1da177e4 | 1260 | |
a07f6033 | 1261 | In this example, the file target maketools will be processed |
5bb78269 | 1262 | before descending down in the subdirectories. |
b26ff488 | 1263 | See also chapter XXX-TODO that describes how kbuild supports |
1da177e4 LT |
1264 | generating offset header files. |
1265 | ||
1266 | ||
e079a08c | 1267 | 7.4 List directories to visit when descending |
cd238eff | 1268 | --------------------------------------------- |
1da177e4 LT |
1269 | |
1270 | An arch Makefile cooperates with the top Makefile to define variables | |
1271 | which specify how to build the vmlinux file. Note that there is no | |
1272 | corresponding arch-specific section for modules; the module-building | |
1273 | machinery is all architecture-independent. | |
1274 | ||
39e6e9cf | 1275 | |
23b53061 | 1276 | head-y, core-y, libs-y, drivers-y |
cd238eff MCC |
1277 | $(head-y) lists objects to be linked first in vmlinux. |
1278 | ||
1279 | $(libs-y) lists directories where a lib.a archive can be located. | |
1280 | ||
1281 | The rest list directories where a built-in.a object file can be | |
1282 | located. | |
1da177e4 | 1283 | |
cd238eff | 1284 | Then the rest follows in this order: |
1da177e4 | 1285 | |
23b53061 | 1286 | $(core-y), $(libs-y), $(drivers-y) |
cd238eff MCC |
1287 | |
1288 | The top level Makefile defines values for all generic directories, | |
8c4d9b14 | 1289 | and arch/$(SRCARCH)/Makefile only adds architecture-specific |
cd238eff MCC |
1290 | directories. |
1291 | ||
1292 | Example:: | |
1da177e4 | 1293 | |
23b53061 MY |
1294 | # arch/sparc/Makefile |
1295 | core-y += arch/sparc/ | |
1296 | ||
1297 | libs-y += arch/sparc/prom/ | |
1298 | libs-y += arch/sparc/lib/ | |
1da177e4 | 1299 | |
23b53061 | 1300 | drivers-$(CONFIG_PM) += arch/sparc/power/ |
1da177e4 | 1301 | |
e079a08c | 1302 | 7.5 Architecture-specific boot images |
cd238eff | 1303 | ------------------------------------- |
1da177e4 LT |
1304 | |
1305 | An arch Makefile specifies goals that take the vmlinux file, compress | |
1306 | it, wrap it in bootstrapping code, and copy the resulting files | |
1307 | somewhere. This includes various kinds of installation commands. | |
1308 | The actual goals are not standardized across architectures. | |
1309 | ||
1310 | It is common to locate any additional processing in a boot/ | |
8c4d9b14 | 1311 | directory below arch/$(SRCARCH)/. |
1da177e4 LT |
1312 | |
1313 | Kbuild does not provide any smart way to support building a | |
8c4d9b14 | 1314 | target specified in boot/. Therefore arch/$(SRCARCH)/Makefile shall |
1da177e4 LT |
1315 | call make manually to build a target in boot/. |
1316 | ||
1317 | The recommended approach is to include shortcuts in | |
8c4d9b14 MY |
1318 | arch/$(SRCARCH)/Makefile, and use the full path when calling down |
1319 | into the arch/$(SRCARCH)/boot/Makefile. | |
1da177e4 | 1320 | |
cd238eff MCC |
1321 | Example:: |
1322 | ||
25eb650a WG |
1323 | #arch/x86/Makefile |
1324 | boot := arch/x86/boot | |
1da177e4 LT |
1325 | bzImage: vmlinux |
1326 | $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ | |
1327 | ||
1328 | "$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke | |
1329 | make in a subdirectory. | |
1330 | ||
5c811e59 | 1331 | There are no rules for naming architecture-specific targets, |
1da177e4 | 1332 | but executing "make help" will list all relevant targets. |
a07f6033 | 1333 | To support this, $(archhelp) must be defined. |
1da177e4 | 1334 | |
cd238eff MCC |
1335 | Example:: |
1336 | ||
25eb650a | 1337 | #arch/x86/Makefile |
1da177e4 | 1338 | define archhelp |
8c4d9b14 | 1339 | echo '* bzImage - Compressed kernel image (arch/x86/boot/bzImage)' |
39e6e9cf | 1340 | endif |
1da177e4 LT |
1341 | |
1342 | When make is executed without arguments, the first goal encountered | |
1343 | will be built. In the top level Makefile the first goal present | |
1344 | is all:. | |
a07f6033 JE |
1345 | An architecture shall always, per default, build a bootable image. |
1346 | In "make help", the default goal is highlighted with a '*'. | |
1da177e4 LT |
1347 | Add a new prerequisite to all: to select a default goal different |
1348 | from vmlinux. | |
1349 | ||
cd238eff MCC |
1350 | Example:: |
1351 | ||
25eb650a | 1352 | #arch/x86/Makefile |
39e6e9cf | 1353 | all: bzImage |
1da177e4 LT |
1354 | |
1355 | When "make" is executed without arguments, bzImage will be built. | |
1356 | ||
e079a08c | 1357 | 7.7 Commands useful for building a boot image |
cd238eff | 1358 | --------------------------------------------- |
1da177e4 | 1359 | |
cd238eff MCC |
1360 | Kbuild provides a few macros that are useful when building a |
1361 | boot image. | |
1da177e4 | 1362 | |
1da177e4 | 1363 | ld |
a07f6033 | 1364 | Link target. Often, LDFLAGS_$@ is used to set specific options to ld. |
39e6e9cf | 1365 | |
cd238eff MCC |
1366 | Example:: |
1367 | ||
25eb650a | 1368 | #arch/x86/boot/Makefile |
1da177e4 LT |
1369 | LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary |
1370 | LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext | |
1371 | ||
1372 | targets += setup setup.o bootsect bootsect.o | |
1373 | $(obj)/setup $(obj)/bootsect: %: %.o FORCE | |
1374 | $(call if_changed,ld) | |
1375 | ||
a07f6033 JE |
1376 | In this example, there are two possible targets, requiring different |
1377 | options to the linker. The linker options are specified using the | |
1da177e4 | 1378 | LDFLAGS_$@ syntax - one for each potential target. |
5d3f083d | 1379 | $(targets) are assigned all potential targets, by which kbuild knows |
1da177e4 | 1380 | the targets and will: |
cd238eff | 1381 | |
1da177e4 LT |
1382 | 1) check for commandline changes |
1383 | 2) delete target during make clean | |
1384 | ||
1385 | The ": %: %.o" part of the prerequisite is a shorthand that | |
39fed701 | 1386 | frees us from listing the setup.o and bootsect.o files. |
cd238eff MCC |
1387 | |
1388 | Note: | |
1389 | It is a common mistake to forget the "targets :=" assignment, | |
1da177e4 LT |
1390 | resulting in the target file being recompiled for no |
1391 | obvious reason. | |
1392 | ||
d87e47e1 C |
1393 | objcopy |
1394 | Copy binary. Uses OBJCOPYFLAGS usually specified in | |
8c4d9b14 | 1395 | arch/$(SRCARCH)/Makefile. |
d87e47e1 C |
1396 | OBJCOPYFLAGS_$@ may be used to set additional options. |
1397 | ||
1398 | gzip | |
1399 | Compress target. Use maximum compression to compress target. | |
1400 | ||
cd238eff MCC |
1401 | Example:: |
1402 | ||
d87e47e1 C |
1403 | #arch/x86/boot/compressed/Makefile |
1404 | $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE | |
1405 | $(call if_changed,gzip) | |
1406 | ||
aab94339 | 1407 | dtc |
c1410562 | 1408 | Create flattened device tree blob object suitable for linking |
aab94339 DB |
1409 | into vmlinux. Device tree blobs linked into vmlinux are placed |
1410 | in an init section in the image. Platform code *must* copy the | |
1411 | blob to non-init memory prior to calling unflatten_device_tree(). | |
1412 | ||
cd238eff MCC |
1413 | To use this command, simply add `*.dtb` into obj-y or targets, or make |
1414 | some other target depend on `%.dtb` | |
aab94339 | 1415 | |
cd238eff | 1416 | A central rule exists to create `$(obj)/%.dtb` from `$(src)/%.dts`; |
90b335fb | 1417 | architecture Makefiles do no need to explicitly write out that rule. |
aab94339 | 1418 | |
cd238eff MCC |
1419 | Example:: |
1420 | ||
90b335fb | 1421 | targets += $(dtb-y) |
90b335fb | 1422 | DTC_FLAGS ?= -p 1024 |
1da177e4 | 1423 | |
e079a08c | 1424 | 7.9 Preprocessing linker scripts |
ff4634ee | 1425 | -------------------------------- |
1da177e4 | 1426 | |
a07f6033 | 1427 | When the vmlinux image is built, the linker script |
8c4d9b14 | 1428 | arch/$(SRCARCH)/kernel/vmlinux.lds is used. |
1da177e4 LT |
1429 | The script is a preprocessed variant of the file vmlinux.lds.S |
1430 | located in the same directory. | |
cd238eff MCC |
1431 | kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`. |
1432 | ||
1433 | Example:: | |
39e6e9cf | 1434 | |
25eb650a | 1435 | #arch/x86/kernel/Makefile |
faa7bdd7 | 1436 | extra-y := vmlinux.lds |
39e6e9cf | 1437 | |
faa7bdd7 | 1438 | The assignment to extra-y is used to tell kbuild to build the |
a07f6033 JE |
1439 | target vmlinux.lds. |
1440 | The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the | |
1da177e4 | 1441 | specified options when building the target vmlinux.lds. |
39e6e9cf | 1442 | |
cd238eff MCC |
1443 | When building the `*.lds` target, kbuild uses the variables:: |
1444 | ||
1445 | KBUILD_CPPFLAGS : Set in top-level Makefile | |
1446 | cppflags-y : May be set in the kbuild makefile | |
1447 | CPPFLAGS_$(@F) : Target-specific flags. | |
1448 | Note that the full filename is used in this | |
1449 | assignment. | |
1da177e4 | 1450 | |
cd238eff | 1451 | The kbuild infrastructure for `*lds` files is used in several |
5c811e59 | 1452 | architecture-specific files. |
1da177e4 | 1453 | |
e079a08c | 1454 | 7.10 Generic header files |
cd238eff | 1455 | ------------------------- |
d8ecc5cd SR |
1456 | |
1457 | The directory include/asm-generic contains the header files | |
1458 | that may be shared between individual architectures. | |
1459 | The recommended approach how to use a generic header file is | |
1460 | to list the file in the Kbuild file. | |
b26ff488 | 1461 | See "8.2 generic-y" for further info on syntax etc. |
d8ecc5cd | 1462 | |
e079a08c | 1463 | 7.11 Post-link pass |
cd238eff | 1464 | ------------------- |
fbe6e37d NP |
1465 | |
1466 | If the file arch/xxx/Makefile.postlink exists, this makefile | |
1467 | will be invoked for post-link objects (vmlinux and modules.ko) | |
1468 | for architectures to run post-link passes on. Must also handle | |
1469 | the clean target. | |
1470 | ||
1471 | This pass runs after kallsyms generation. If the architecture | |
1472 | needs to modify symbol locations, rather than manipulate the | |
1473 | kallsyms, it may be easier to add another postlink target for | |
1474 | .tmp_vmlinux? targets to be called from link-vmlinux.sh. | |
1475 | ||
1476 | For example, powerpc uses this to check relocation sanity of | |
1477 | the linked vmlinux file. | |
1478 | ||
e079a08c | 1479 | 8 Kbuild syntax for exported headers |
cd238eff | 1480 | ------------------------------------ |
c7bb349e | 1481 | |
39fed701 | 1482 | The kernel includes a set of headers that is exported to userspace. |
c95940f2 | 1483 | Many headers can be exported as-is but other headers require a |
c7bb349e SR |
1484 | minimal pre-processing before they are ready for user-space. |
1485 | The pre-processing does: | |
cd238eff | 1486 | |
39fed701 | 1487 | - drop kernel-specific annotations |
c7bb349e | 1488 | - drop include of compiler.h |
cd238eff | 1489 | - drop all sections that are kernel internal (guarded by `ifdef __KERNEL__`) |
c7bb349e | 1490 | |
fcc8487d | 1491 | All headers under include/uapi/, include/generated/uapi/, |
61562f98 | 1492 | arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/ |
fcc8487d | 1493 | are exported. |
c7bb349e | 1494 | |
fcc8487d ND |
1495 | A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and |
1496 | arch/<arch>/include/asm/ to list asm files coming from asm-generic. | |
1497 | See subsequent chapter for the syntax of the Kbuild file. | |
c7bb349e | 1498 | |
e079a08c | 1499 | 8.1 no-export-headers |
cd238eff | 1500 | --------------------- |
c7bb349e | 1501 | |
fcc8487d ND |
1502 | no-export-headers is essentially used by include/uapi/linux/Kbuild to |
1503 | avoid exporting specific headers (e.g. kvm.h) on architectures that do | |
1504 | not support it. It should be avoided as much as possible. | |
c7bb349e | 1505 | |
e079a08c | 1506 | 8.2 generic-y |
cd238eff | 1507 | ------------- |
d8ecc5cd SR |
1508 | |
1509 | If an architecture uses a verbatim copy of a header from | |
1510 | include/asm-generic then this is listed in the file | |
8c4d9b14 | 1511 | arch/$(SRCARCH)/include/asm/Kbuild like this: |
d8ecc5cd | 1512 | |
cd238eff MCC |
1513 | Example:: |
1514 | ||
d8ecc5cd SR |
1515 | #arch/x86/include/asm/Kbuild |
1516 | generic-y += termios.h | |
1517 | generic-y += rtc.h | |
1518 | ||
1519 | During the prepare phase of the build a wrapper include | |
cd238eff | 1520 | file is generated in the directory:: |
d8ecc5cd | 1521 | |
8c4d9b14 | 1522 | arch/$(SRCARCH)/include/generated/asm |
d8ecc5cd SR |
1523 | |
1524 | When a header is exported where the architecture uses | |
1525 | the generic header a similar wrapper is generated as part | |
cd238eff | 1526 | of the set of exported headers in the directory:: |
d8ecc5cd SR |
1527 | |
1528 | usr/include/asm | |
1529 | ||
1530 | The generated wrapper will in both cases look like the following: | |
1531 | ||
cd238eff MCC |
1532 | Example: termios.h:: |
1533 | ||
d8ecc5cd | 1534 | #include <asm-generic/termios.h> |
c7bb349e | 1535 | |
e079a08c | 1536 | 8.3 generated-y |
cd238eff | 1537 | --------------- |
54b880ca JH |
1538 | |
1539 | If an architecture generates other header files alongside generic-y | |
ae3f4151 | 1540 | wrappers, generated-y specifies them. |
54b880ca JH |
1541 | |
1542 | This prevents them being treated as stale asm-generic wrappers and | |
1543 | removed. | |
1544 | ||
cd238eff MCC |
1545 | Example:: |
1546 | ||
54b880ca JH |
1547 | #arch/x86/include/asm/Kbuild |
1548 | generated-y += syscalls_32.h | |
1549 | ||
e079a08c | 1550 | 8.4 mandatory-y |
cd238eff | 1551 | --------------- |
fcc8487d | 1552 | |
037fc336 | 1553 | mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild |
91998731 MY |
1554 | to define the minimum set of ASM headers that all architectures must have. |
1555 | ||
1556 | This works like optional generic-y. If a mandatory header is missing | |
8c4d9b14 MY |
1557 | in arch/$(SRCARCH)/include/(uapi/)/asm, Kbuild will automatically |
1558 | generate a wrapper of the asm-generic one. | |
fcc8487d | 1559 | |
e079a08c | 1560 | 9 Kbuild Variables |
cd238eff | 1561 | ================== |
1da177e4 LT |
1562 | |
1563 | The top Makefile exports the following variables: | |
1564 | ||
1565 | VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION | |
1da177e4 LT |
1566 | These variables define the current kernel version. A few arch |
1567 | Makefiles actually use these values directly; they should use | |
1568 | $(KERNELRELEASE) instead. | |
1569 | ||
1570 | $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic | |
1571 | three-part version number, such as "2", "4", and "0". These three | |
1572 | values are always numeric. | |
1573 | ||
1574 | $(EXTRAVERSION) defines an even tinier sublevel for pre-patches | |
1575 | or additional patches. It is usually some non-numeric string | |
1576 | such as "-pre4", and is often blank. | |
1577 | ||
1578 | KERNELRELEASE | |
1da177e4 LT |
1579 | $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable |
1580 | for constructing installation directory names or showing in | |
1581 | version strings. Some arch Makefiles use it for this purpose. | |
1582 | ||
1583 | ARCH | |
1da177e4 LT |
1584 | This variable defines the target architecture, such as "i386", |
1585 | "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to | |
1586 | determine which files to compile. | |
1587 | ||
1588 | By default, the top Makefile sets $(ARCH) to be the same as the | |
1589 | host system architecture. For a cross build, a user may | |
cd238eff | 1590 | override the value of $(ARCH) on the command line:: |
1da177e4 LT |
1591 | |
1592 | make ARCH=m68k ... | |
1593 | ||
8c4d9b14 MY |
1594 | SRCARCH |
1595 | This variable specifies the directory in arch/ to build. | |
1596 | ||
1597 | ARCH and SRCARCH may not necessarily match. A couple of arch | |
1598 | directories are biarch, that is, a single `arch/*/` directory supports | |
1599 | both 32-bit and 64-bit. | |
1600 | ||
1601 | For example, you can pass in ARCH=i386, ARCH=x86_64, or ARCH=x86. | |
1602 | For all of them, SRCARCH=x86 because arch/x86/ supports both i386 and | |
1603 | x86_64. | |
1da177e4 LT |
1604 | |
1605 | INSTALL_PATH | |
1da177e4 LT |
1606 | This variable defines a place for the arch Makefiles to install |
1607 | the resident kernel image and System.map file. | |
5c811e59 | 1608 | Use this for architecture-specific install targets. |
1da177e4 LT |
1609 | |
1610 | INSTALL_MOD_PATH, MODLIB | |
1da177e4 LT |
1611 | $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module |
1612 | installation. This variable is not defined in the Makefile but | |
1613 | may be passed in by the user if desired. | |
1614 | ||
1615 | $(MODLIB) specifies the directory for module installation. | |
1616 | The top Makefile defines $(MODLIB) to | |
1617 | $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may | |
1618 | override this value on the command line if desired. | |
1619 | ||
ac031f26 | 1620 | INSTALL_MOD_STRIP |
39fed701 | 1621 | If this variable is specified, it will cause modules to be stripped |
ac031f26 | 1622 | after they are installed. If INSTALL_MOD_STRIP is '1', then the |
39fed701 | 1623 | default option --strip-debug will be used. Otherwise, the |
177b241d GE |
1624 | INSTALL_MOD_STRIP value will be used as the option(s) to the strip |
1625 | command. | |
ac031f26 TT |
1626 | |
1627 | ||
e079a08c MY |
1628 | 10 Makefile language |
1629 | ==================== | |
1da177e4 | 1630 | |
a07f6033 | 1631 | The kernel Makefiles are designed to be run with GNU Make. The Makefiles |
1da177e4 LT |
1632 | use only the documented features of GNU Make, but they do use many |
1633 | GNU extensions. | |
1634 | ||
1635 | GNU Make supports elementary list-processing functions. The kernel | |
1636 | Makefiles use a novel style of list building and manipulation with few | |
1637 | "if" statements. | |
1638 | ||
1639 | GNU Make has two assignment operators, ":=" and "=". ":=" performs | |
1640 | immediate evaluation of the right-hand side and stores an actual string | |
1641 | into the left-hand side. "=" is like a formula definition; it stores the | |
1642 | right-hand side in an unevaluated form and then evaluates this form each | |
1643 | time the left-hand side is used. | |
1644 | ||
1645 | There are some cases where "=" is appropriate. Usually, though, ":=" | |
1646 | is the right choice. | |
1647 | ||
e079a08c | 1648 | 11 Credits |
cd238eff | 1649 | ========== |
1da177e4 | 1650 | |
cd238eff MCC |
1651 | - Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> |
1652 | - Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de> | |
1653 | - Updates by Sam Ravnborg <sam@ravnborg.org> | |
1654 | - Language QA by Jan Engelhardt <jengelh@gmx.de> | |
1da177e4 | 1655 | |
e079a08c | 1656 | 12 TODO |
cd238eff | 1657 | ======= |
1da177e4 | 1658 | |
a07f6033 | 1659 | - Describe how kbuild supports shipped files with _shipped. |
1da177e4 | 1660 | - Generating offset header files. |
b26ff488 | 1661 | - Add more variables to chapters 7 or 9? |