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Diffstat (limited to 'Documentation/kbuild/modules.txt')
-rw-r--r-- | Documentation/kbuild/modules.txt | 119 |
1 files changed, 60 insertions, 59 deletions
diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt index 61fc079eb966..a2a178da02ff 100644 --- a/Documentation/kbuild/modules.txt +++ b/Documentation/kbuild/modules.txt | |||
@@ -1,7 +1,7 @@ | |||
1 | 1 | ||
2 | In this document you will find information about: | 2 | In this document you will find information about: |
3 | - how to build external modules | 3 | - how to build external modules |
4 | - how to make your module use kbuild infrastructure | 4 | - how to make your module use the kbuild infrastructure |
5 | - how kbuild will install a kernel | 5 | - how kbuild will install a kernel |
6 | - how to install modules in a non-standard location | 6 | - how to install modules in a non-standard location |
7 | 7 | ||
@@ -36,13 +36,13 @@ In this document you will find information about: | |||
36 | 36 | ||
37 | kbuild includes functionality for building modules both | 37 | kbuild includes functionality for building modules both |
38 | within the kernel source tree and outside the kernel source tree. | 38 | within the kernel source tree and outside the kernel source tree. |
39 | The latter is usually referred to as external modules and is used | 39 | The latter is usually referred to as external or "out-of-tree" |
40 | both during development and for modules that are not planned to be | 40 | modules and is used both during development and for modules that |
41 | included in the kernel tree. | 41 | are not planned to be included in the kernel tree. |
42 | 42 | ||
43 | What is covered within this file is mainly information to authors | 43 | What is covered within this file is mainly information to authors |
44 | of modules. The author of an external modules should supply | 44 | of modules. The author of an external module should supply |
45 | a makefile that hides most of the complexity so one only has to type | 45 | a makefile that hides most of the complexity, so one only has to type |
46 | 'make' to build the module. A complete example will be present in | 46 | 'make' to build the module. A complete example will be present in |
47 | chapter 4, "Creating a kbuild file for an external module". | 47 | chapter 4, "Creating a kbuild file for an external module". |
48 | 48 | ||
@@ -137,7 +137,7 @@ when building an external module. | |||
137 | module versioning work. | 137 | module versioning work. |
138 | 138 | ||
139 | --- 2.5 Building separate files for a module | 139 | --- 2.5 Building separate files for a module |
140 | It is possible to build single files which is part of a module. | 140 | It is possible to build single files which are part of a module. |
141 | This works equal for the kernel, a module and even for external | 141 | This works equal for the kernel, a module and even for external |
142 | modules. | 142 | modules. |
143 | Examples (module foo.ko, consist of bar.o, baz.o): | 143 | Examples (module foo.ko, consist of bar.o, baz.o): |
@@ -151,7 +151,7 @@ when building an external module. | |||
151 | 151 | ||
152 | This example shows the actual commands to be executed when building | 152 | This example shows the actual commands to be executed when building |
153 | an external module for the currently running kernel. | 153 | an external module for the currently running kernel. |
154 | In the example below the distribution is supposed to use the | 154 | In the example below, the distribution is supposed to use the |
155 | facility to locate output files for a kernel compile in a different | 155 | facility to locate output files for a kernel compile in a different |
156 | directory than the kernel source - but the examples will also work | 156 | directory than the kernel source - but the examples will also work |
157 | when the source and the output files are mixed in the same directory. | 157 | when the source and the output files are mixed in the same directory. |
@@ -170,7 +170,7 @@ the following commands to build the module: | |||
170 | O=/lib/modules/`uname-r`/build \ | 170 | O=/lib/modules/`uname-r`/build \ |
171 | M=`pwd` | 171 | M=`pwd` |
172 | 172 | ||
173 | Then to install the module use the following command: | 173 | Then, to install the module use the following command: |
174 | 174 | ||
175 | make -C /usr/src/`uname -r`/source \ | 175 | make -C /usr/src/`uname -r`/source \ |
176 | O=/lib/modules/`uname-r`/build \ | 176 | O=/lib/modules/`uname-r`/build \ |
@@ -230,7 +230,7 @@ following files: | |||
230 | 230 | ||
231 | endif | 231 | endif |
232 | 232 | ||
233 | In example 1 the check for KERNELRELEASE is used to separate | 233 | In example 1, the check for KERNELRELEASE is used to separate |
234 | the two parts of the Makefile. kbuild will only see the two | 234 | the two parts of the Makefile. kbuild will only see the two |
235 | assignments whereas make will see everything except the two | 235 | assignments whereas make will see everything except the two |
236 | kbuild assignments. | 236 | kbuild assignments. |
@@ -255,7 +255,7 @@ following files: | |||
255 | echo "X" > 8123_bin_shipped | 255 | echo "X" > 8123_bin_shipped |
256 | 256 | ||
257 | 257 | ||
258 | In example 2 we are down to two fairly simple files and for simple | 258 | In example 2, we are down to two fairly simple files and for simple |
259 | files as used in this example the split is questionable. But some | 259 | files as used in this example the split is questionable. But some |
260 | external modules use Makefiles of several hundred lines and here it | 260 | external modules use Makefiles of several hundred lines and here it |
261 | really pays off to separate the kbuild part from the rest. | 261 | really pays off to separate the kbuild part from the rest. |
@@ -282,9 +282,9 @@ following files: | |||
282 | 282 | ||
283 | endif | 283 | endif |
284 | 284 | ||
285 | The trick here is to include the Kbuild file from Makefile so | 285 | The trick here is to include the Kbuild file from Makefile, so |
286 | if an older version of kbuild picks up the Makefile the Kbuild | 286 | if an older version of kbuild picks up the Makefile, the Kbuild |
287 | file will be included. | 287 | file will be included. |
288 | 288 | ||
289 | --- 4.2 Binary blobs included in a module | 289 | --- 4.2 Binary blobs included in a module |
290 | 290 | ||
@@ -301,18 +301,19 @@ following files: | |||
301 | obj-m := 8123.o | 301 | obj-m := 8123.o |
302 | 8123-y := 8123_if.o 8123_pci.o 8123_bin.o | 302 | 8123-y := 8123_if.o 8123_pci.o 8123_bin.o |
303 | 303 | ||
304 | In example 4 there is no distinction between the ordinary .c/.h files | 304 | In example 4, there is no distinction between the ordinary .c/.h files |
305 | and the binary file. But kbuild will pick up different rules to create | 305 | and the binary file. But kbuild will pick up different rules to create |
306 | the .o file. | 306 | the .o file. |
307 | 307 | ||
308 | 308 | ||
309 | === 5. Include files | 309 | === 5. Include files |
310 | 310 | ||
311 | Include files are a necessity when a .c file uses something from another .c | 311 | Include files are a necessity when a .c file uses something from other .c |
312 | files (not strictly in the sense of .c but if good programming practice is | 312 | files (not strictly in the sense of C, but if good programming practice is |
313 | used). Any module that consist of more than one .c file will have a .h file | 313 | used). Any module that consists of more than one .c file will have a .h file |
314 | for one of the .c files. | 314 | for one of the .c files. |
315 | - If the .h file only describes a module internal interface then the .h file | 315 | |
316 | - If the .h file only describes a module internal interface, then the .h file | ||
316 | shall be placed in the same directory as the .c files. | 317 | shall be placed in the same directory as the .c files. |
317 | - If the .h files describe an interface used by other parts of the kernel | 318 | - If the .h files describe an interface used by other parts of the kernel |
318 | located in different directories, the .h files shall be located in | 319 | located in different directories, the .h files shall be located in |
@@ -323,11 +324,11 @@ under include/ such as include/scsi. Another exception is arch-specific | |||
323 | .h files which are located under include/asm-$(ARCH)/*. | 324 | .h files which are located under include/asm-$(ARCH)/*. |
324 | 325 | ||
325 | External modules have a tendency to locate include files in a separate include/ | 326 | External modules have a tendency to locate include files in a separate include/ |
326 | directory and therefore needs to deal with this in their kbuild file. | 327 | directory and therefore need to deal with this in their kbuild file. |
327 | 328 | ||
328 | --- 5.1 How to include files from the kernel include dir | 329 | --- 5.1 How to include files from the kernel include dir |
329 | 330 | ||
330 | When a module needs to include a file from include/linux/ then one | 331 | When a module needs to include a file from include/linux/, then one |
331 | just uses: | 332 | just uses: |
332 | 333 | ||
333 | #include <linux/modules.h> | 334 | #include <linux/modules.h> |
@@ -348,7 +349,7 @@ directory and therefore needs to deal with this in their kbuild file. | |||
348 | The trick here is to use either EXTRA_CFLAGS (take effect for all .c | 349 | The trick here is to use either EXTRA_CFLAGS (take effect for all .c |
349 | files) or CFLAGS_$F.o (take effect only for a single file). | 350 | files) or CFLAGS_$F.o (take effect only for a single file). |
350 | 351 | ||
351 | In our example if we move 8123_if.h to a subdirectory named include/ | 352 | In our example, if we move 8123_if.h to a subdirectory named include/ |
352 | the resulting Kbuild file would look like: | 353 | the resulting Kbuild file would look like: |
353 | 354 | ||
354 | --> filename: Kbuild | 355 | --> filename: Kbuild |
@@ -362,9 +363,9 @@ directory and therefore needs to deal with this in their kbuild file. | |||
362 | 363 | ||
363 | --- 5.3 External modules using several directories | 364 | --- 5.3 External modules using several directories |
364 | 365 | ||
365 | If an external module does not follow the usual kernel style but | 366 | If an external module does not follow the usual kernel style, but |
366 | decide to spread files over several directories then kbuild can | 367 | decides to spread files over several directories, then kbuild can |
367 | support this too. | 368 | handle this too. |
368 | 369 | ||
369 | Consider the following example: | 370 | Consider the following example: |
370 | 371 | ||
@@ -374,7 +375,7 @@ directory and therefore needs to deal with this in their kbuild file. | |||
374 | | +- hal/include/hardwareif.h | 375 | | +- hal/include/hardwareif.h |
375 | +- include/complex.h | 376 | +- include/complex.h |
376 | 377 | ||
377 | To build a single module named complex.ko we then need the following | 378 | To build a single module named complex.ko, we then need the following |
378 | kbuild file: | 379 | kbuild file: |
379 | 380 | ||
380 | Kbuild: | 381 | Kbuild: |
@@ -387,12 +388,12 @@ directory and therefore needs to deal with this in their kbuild file. | |||
387 | 388 | ||
388 | 389 | ||
389 | kbuild knows how to handle .o files located in another directory - | 390 | kbuild knows how to handle .o files located in another directory - |
390 | although this is NOT reccommended practice. The syntax is to specify | 391 | although this is NOT recommended practice. The syntax is to specify |
391 | the directory relative to the directory where the Kbuild file is | 392 | the directory relative to the directory where the Kbuild file is |
392 | located. | 393 | located. |
393 | 394 | ||
394 | To find the .h files we have to explicitly tell kbuild where to look | 395 | To find the .h files, we have to explicitly tell kbuild where to look |
395 | for the .h files. When kbuild executes current directory is always | 396 | for the .h files. When kbuild executes, the current directory is always |
396 | the root of the kernel tree (argument to -C) and therefore we have to | 397 | the root of the kernel tree (argument to -C) and therefore we have to |
397 | tell kbuild how to find the .h files using absolute paths. | 398 | tell kbuild how to find the .h files using absolute paths. |
398 | $(src) will specify the absolute path to the directory where the | 399 | $(src) will specify the absolute path to the directory where the |
@@ -412,7 +413,7 @@ External modules are installed in the directory: | |||
412 | 413 | ||
413 | --- 6.1 INSTALL_MOD_PATH | 414 | --- 6.1 INSTALL_MOD_PATH |
414 | 415 | ||
415 | Above are the default directories, but as always some level of | 416 | Above are the default directories, but as always, some level of |
416 | customization is possible. One can prefix the path using the variable | 417 | customization is possible. One can prefix the path using the variable |
417 | INSTALL_MOD_PATH: | 418 | INSTALL_MOD_PATH: |
418 | 419 | ||
@@ -420,17 +421,17 @@ External modules are installed in the directory: | |||
420 | => Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel | 421 | => Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel |
421 | 422 | ||
422 | INSTALL_MOD_PATH may be set as an ordinary shell variable or as in the | 423 | INSTALL_MOD_PATH may be set as an ordinary shell variable or as in the |
423 | example above be specified on the command line when calling make. | 424 | example above, can be specified on the command line when calling make. |
424 | INSTALL_MOD_PATH has effect both when installing modules included in | 425 | INSTALL_MOD_PATH has effect both when installing modules included in |
425 | the kernel as well as when installing external modules. | 426 | the kernel as well as when installing external modules. |
426 | 427 | ||
427 | --- 6.2 INSTALL_MOD_DIR | 428 | --- 6.2 INSTALL_MOD_DIR |
428 | 429 | ||
429 | When installing external modules they are default installed in a | 430 | When installing external modules they are by default installed to a |
430 | directory under /lib/modules/$(KERNELRELEASE)/extra, but one may wish | 431 | directory under /lib/modules/$(KERNELRELEASE)/extra, but one may wish |
431 | to locate modules for a specific functionality in a separate | 432 | to locate modules for a specific functionality in a separate |
432 | directory. For this purpose one can use INSTALL_MOD_DIR to specify an | 433 | directory. For this purpose, one can use INSTALL_MOD_DIR to specify an |
433 | alternative name than 'extra'. | 434 | alternative name to 'extra'. |
434 | 435 | ||
435 | $ make INSTALL_MOD_DIR=gandalf -C KERNELDIR \ | 436 | $ make INSTALL_MOD_DIR=gandalf -C KERNELDIR \ |
436 | M=`pwd` modules_install | 437 | M=`pwd` modules_install |
@@ -444,16 +445,16 @@ Module versioning is enabled by the CONFIG_MODVERSIONS tag. | |||
444 | Module versioning is used as a simple ABI consistency check. The Module | 445 | Module versioning is used as a simple ABI consistency check. The Module |
445 | versioning creates a CRC value of the full prototype for an exported symbol and | 446 | versioning creates a CRC value of the full prototype for an exported symbol and |
446 | when a module is loaded/used then the CRC values contained in the kernel are | 447 | when a module is loaded/used then the CRC values contained in the kernel are |
447 | compared with similar values in the module. If they are not equal then the | 448 | compared with similar values in the module. If they are not equal, then the |
448 | kernel refuses to load the module. | 449 | kernel refuses to load the module. |
449 | 450 | ||
450 | Module.symvers contains a list of all exported symbols from a kernel build. | 451 | Module.symvers contains a list of all exported symbols from a kernel build. |
451 | 452 | ||
452 | --- 7.1 Symbols fron the kernel (vmlinux + modules) | 453 | --- 7.1 Symbols fron the kernel (vmlinux + modules) |
453 | 454 | ||
454 | During a kernel build a file named Module.symvers will be generated. | 455 | During a kernel build, a file named Module.symvers will be generated. |
455 | Module.symvers contains all exported symbols from the kernel and | 456 | Module.symvers contains all exported symbols from the kernel and |
456 | compiled modules. For each symbols the corresponding CRC value | 457 | compiled modules. For each symbols, the corresponding CRC value |
457 | is stored too. | 458 | is stored too. |
458 | 459 | ||
459 | The syntax of the Module.symvers file is: | 460 | The syntax of the Module.symvers file is: |
@@ -461,27 +462,27 @@ Module.symvers contains a list of all exported symbols from a kernel build. | |||
461 | Sample: | 462 | Sample: |
462 | 0x2d036834 scsi_remove_host drivers/scsi/scsi_mod | 463 | 0x2d036834 scsi_remove_host drivers/scsi/scsi_mod |
463 | 464 | ||
464 | For a kernel build without CONFIG_MODVERSIONING enabled the crc | 465 | For a kernel build without CONFIG_MODVERSIONING enabled, the crc |
465 | would read: 0x00000000 | 466 | would read: 0x00000000 |
466 | 467 | ||
467 | Module.symvers serve two purposes. | 468 | Module.symvers serves two purposes: |
468 | 1) It list all exported symbols both from vmlinux and all modules | 469 | 1) It lists all exported symbols both from vmlinux and all modules |
469 | 2) It list CRC if CONFIG_MODVERSION is enabled | 470 | 2) It lists the CRC if CONFIG_MODVERSION is enabled |
470 | 471 | ||
471 | --- 7.2 Symbols and external modules | 472 | --- 7.2 Symbols and external modules |
472 | 473 | ||
473 | When building an external module the build system needs access to | 474 | When building an external module, the build system needs access to |
474 | the symbols from the kernel to check if all external symbols are | 475 | the symbols from the kernel to check if all external symbols are |
475 | defined. This is done in the MODPOST step and to obtain all | 476 | defined. This is done in the MODPOST step and to obtain all |
476 | symbols modpost reads Module.symvers from the kernel. | 477 | symbols, modpost reads Module.symvers from the kernel. |
477 | If a Module.symvers file is present in the directory where | 478 | If a Module.symvers file is present in the directory where |
478 | the external module is being build this file will be read too. | 479 | the external module is being built, this file will be read too. |
479 | During the MODPOST step a new Module.symvers file will be written | 480 | During the MODPOST step, a new Module.symvers file will be written |
480 | containing all exported symbols that was not defined in the kernel. | 481 | containing all exported symbols that were not defined in the kernel. |
481 | 482 | ||
482 | --- 7.3 Symbols from another external module | 483 | --- 7.3 Symbols from another external module |
483 | 484 | ||
484 | Sometimes one external module uses exported symbols from another | 485 | Sometimes, an external module uses exported symbols from another |
485 | external module. Kbuild needs to have full knowledge on all symbols | 486 | external module. Kbuild needs to have full knowledge on all symbols |
486 | to avoid spitting out warnings about undefined symbols. | 487 | to avoid spitting out warnings about undefined symbols. |
487 | Two solutions exist to let kbuild know all symbols of more than | 488 | Two solutions exist to let kbuild know all symbols of more than |
@@ -490,9 +491,9 @@ Module.symvers contains a list of all exported symbols from a kernel build. | |||
490 | impractical in certain situations. | 491 | impractical in certain situations. |
491 | 492 | ||
492 | Use a top-level Kbuild file | 493 | Use a top-level Kbuild file |
493 | If you have two modules: 'foo', 'bar' and 'foo' needs symbols | 494 | If you have two modules: 'foo' and 'bar', and 'foo' needs |
494 | from 'bar' then one can use a common top-level kbuild file so | 495 | symbols from 'bar', then one can use a common top-level kbuild |
495 | both modules are compiled in same build. | 496 | file so both modules are compiled in same build. |
496 | 497 | ||
497 | Consider following directory layout: | 498 | Consider following directory layout: |
498 | ./foo/ <= contains the foo module | 499 | ./foo/ <= contains the foo module |
@@ -509,15 +510,15 @@ Module.symvers contains a list of all exported symbols from a kernel build. | |||
509 | knowledge on symbols from both modules. | 510 | knowledge on symbols from both modules. |
510 | 511 | ||
511 | Use an extra Module.symvers file | 512 | Use an extra Module.symvers file |
512 | When an external module is build a Module.symvers file is | 513 | When an external module is built, a Module.symvers file is |
513 | generated containing all exported symbols which are not | 514 | generated containing all exported symbols which are not |
514 | defined in the kernel. | 515 | defined in the kernel. |
515 | To get access to symbols from module 'bar' one can copy the | 516 | To get access to symbols from module 'bar', one can copy the |
516 | Module.symvers file from the compilation of the 'bar' module | 517 | Module.symvers file from the compilation of the 'bar' module |
517 | to the directory where the 'foo' module is build. | 518 | to the directory where the 'foo' module is built. |
518 | During the module build kbuild will read the Module.symvers | 519 | During the module build, kbuild will read the Module.symvers |
519 | file in the directory of the external module and when the | 520 | file in the directory of the external module and when the |
520 | build is finished a new Module.symvers file is created | 521 | build is finished, a new Module.symvers file is created |
521 | containing the sum of all symbols defined and not part of the | 522 | containing the sum of all symbols defined and not part of the |
522 | kernel. | 523 | kernel. |
523 | 524 | ||
@@ -525,7 +526,7 @@ Module.symvers contains a list of all exported symbols from a kernel build. | |||
525 | 526 | ||
526 | --- 8.1 Testing for CONFIG_FOO_BAR | 527 | --- 8.1 Testing for CONFIG_FOO_BAR |
527 | 528 | ||
528 | Modules often needs to check for certain CONFIG_ options to decide if | 529 | Modules often need to check for certain CONFIG_ options to decide if |
529 | a specific feature shall be included in the module. When kbuild is used | 530 | a specific feature shall be included in the module. When kbuild is used |
530 | this is done by referencing the CONFIG_ variable directly. | 531 | this is done by referencing the CONFIG_ variable directly. |
531 | 532 | ||
@@ -537,7 +538,7 @@ Module.symvers contains a list of all exported symbols from a kernel build. | |||
537 | 538 | ||
538 | External modules have traditionally used grep to check for specific | 539 | External modules have traditionally used grep to check for specific |
539 | CONFIG_ settings directly in .config. This usage is broken. | 540 | CONFIG_ settings directly in .config. This usage is broken. |
540 | As introduced before external modules shall use kbuild when building | 541 | As introduced before, external modules shall use kbuild when building |
541 | and therefore can use the same methods as in-kernel modules when testing | 542 | and therefore can use the same methods as in-kernel modules when |
542 | for CONFIG_ definitions. | 543 | testing for CONFIG_ definitions. |
543 | 544 | ||