1 .. Copyright 2010 Nicolas Palix <npalix@diku.dk>
2 .. Copyright 2010 Julia Lawall <julia@diku.dk>
3 .. Copyright 2010 Gilles Muller <Gilles.Muller@lip6.fr>
4
5 .. highlight:: none
6
7 .. _devtools_coccinelle:
8
9 Coccinelle
10 ==========
11
12 Coccinelle is a tool for pattern matching and text transformation that has
13 many uses in kernel development, including the application of complex,
14 tree-wide patches and detection of problematic programming patterns.
15
16 Getting Coccinelle
17 ------------------
18
19 The semantic patches included in the kernel use features and options
20 which are provided by Coccinelle version 1.0.0-rc11 and above.
21 Using earlier versions will fail as the option names used by
22 the Coccinelle files and coccicheck have been updated.
23
24 Coccinelle is available through the package manager
25 of many distributions, e.g. :
26
27 - Debian
28 - Fedora
29 - Ubuntu
30 - OpenSUSE
31 - Arch Linux
32 - NetBSD
33 - FreeBSD
34
35 Some distribution packages are obsolete and it is recommended
36 to use the latest version released from the Coccinelle homepage at
37 http://coccinelle.lip6.fr/
38
39 Or from Github at:
40
41 https://github.com/coccinelle/coccinelle
42
43 Once you have it, run the following commands::
44
45 ./autogen
46 ./configure
47 make
48
49 as a regular user, and install it with::
50
51 sudo make install
52
53 More detailed installation instructions to build from source can be
54 found at:
55
56 https://github.com/coccinelle/coccinelle/blob/master/install.txt
57
58 Supplemental documentation
59 --------------------------
60
61 For supplemental documentation refer to the wiki:
62
63 https://bottest.wiki.kernel.org/coccicheck
64
65 The wiki documentation always refers to the linux-next version of the script.
66
67 For Semantic Patch Language(SmPL) grammar documentation refer to:
68
69 https://coccinelle.gitlabpages.inria.fr/website/docs/main_grammar.html
70
71 Using Coccinelle on the Linux kernel
72 ------------------------------------
73
74 A Coccinelle-specific target is defined in the top level
75 Makefile. This target is named ``coccicheck`` and calls the ``coccicheck``
76 front-end in the ``scripts`` directory.
77
78 Four basic modes are defined: ``patch``, ``report``, ``context``, and
79 ``org``. The mode to use is specified by setting the MODE variable with
80 ``MODE=<mode>``.
81
82 - ``patch`` proposes a fix, when possible.
83
84 - ``report`` generates a list in the following format:
85 file:line:column-column: message
86
87 - ``context`` highlights lines of interest and their context in a
88 diff-like style. Lines of interest are indicated with ``-``.
89
90 - ``org`` generates a report in the Org mode format of Emacs.
91
92 Note that not all semantic patches implement all modes. For easy use
93 of Coccinelle, the default mode is "report".
94
95 Two other modes provide some common combinations of these modes.
96
97 - ``chain`` tries the previous modes in the order above until one succeeds.
98
99 - ``rep+ctxt`` runs successively the report mode and the context mode.
100 It should be used with the C option (described later)
101 which checks the code on a file basis.
102
103 Examples
104 ~~~~~~~~
105
106 To make a report for every semantic patch, run the following command::
107
108 make coccicheck MODE=report
109
110 To produce patches, run::
111
112 make coccicheck MODE=patch
113
114
115 The coccicheck target applies every semantic patch available in the
116 sub-directories of ``scripts/coccinelle`` to the entire Linux kernel.
117
118 For each semantic patch, a commit message is proposed. It gives a
119 description of the problem being checked by the semantic patch, and
120 includes a reference to Coccinelle.
121
122 As with any static code analyzer, Coccinelle produces false
123 positives. Thus, reports must be carefully checked, and patches
124 reviewed.
125
126 To enable verbose messages set the V= variable, for example::
127
128 make coccicheck MODE=report V=1
129
130 Coccinelle parallelization
131 --------------------------
132
133 By default, coccicheck tries to run as parallel as possible. To change
134 the parallelism, set the J= variable. For example, to run across 4 CPUs::
135
136 make coccicheck MODE=report J=4
137
138 As of Coccinelle 1.0.2 Coccinelle uses Ocaml parmap for parallelization;
139 if support for this is detected you will benefit from parmap parallelization.
140
141 When parmap is enabled coccicheck will enable dynamic load balancing by using
142 ``--chunksize 1`` argument. This ensures we keep feeding threads with work
143 one by one, so that we avoid the situation where most work gets done by only
144 a few threads. With dynamic load balancing, if a thread finishes early we keep
145 feeding it more work.
146
147 When parmap is enabled, if an error occurs in Coccinelle, this error
148 value is propagated back, and the return value of the ``make coccicheck``
149 command captures this return value.
150
151 Using Coccinelle with a single semantic patch
152 ---------------------------------------------
153
154 The optional make variable COCCI can be used to check a single
155 semantic patch. In that case, the variable must be initialized with
156 the name of the semantic patch to apply.
157
158 For instance::
159
160 make coccicheck COCCI=<my_SP.cocci> MODE=patch
161
162 or::
163
164 make coccicheck COCCI=<my_SP.cocci> MODE=report
165
166
167 Controlling Which Files are Processed by Coccinelle
168 ---------------------------------------------------
169
170 By default the entire kernel source tree is checked.
171
172 To apply Coccinelle to a specific directory, ``M=`` can be used.
173 For example, to check drivers/net/wireless/ one may write::
174
175 make coccicheck M=drivers/net/wireless/
176
177 To apply Coccinelle on a file basis, instead of a directory basis, the
178 C variable is used by the makefile to select which files to work with.
179 This variable can be used to run scripts for the entire kernel, a
180 specific directory, or for a single file.
181
182 For example, to check drivers/bluetooth/bfusb.c, the value 1 is
183 passed to the C variable to check files that make considers
184 need to be compiled.::
185
186 make C=1 CHECK=scripts/coccicheck drivers/bluetooth/bfusb.o
187
188 The value 2 is passed to the C variable to check files regardless of
189 whether they need to be compiled or not.::
190
191 make C=2 CHECK=scripts/coccicheck drivers/bluetooth/bfusb.o
192
193 In these modes, which work on a file basis, there is no information
194 about semantic patches displayed, and no commit message proposed.
195
196 This runs every semantic patch in scripts/coccinelle by default. The
197 COCCI variable may additionally be used to only apply a single
198 semantic patch as shown in the previous section.
199
200 The "report" mode is the default. You can select another one with the
201 MODE variable explained above.
202
203 Debugging Coccinelle SmPL patches
204 ---------------------------------
205
206 Using coccicheck is best as it provides in the spatch command line
207 include options matching the options used when we compile the kernel.
208 You can learn what these options are by using V=1; you could then
209 manually run Coccinelle with debug options added.
210
211 Alternatively you can debug running Coccinelle against SmPL patches
212 by asking for stderr to be redirected to stderr. By default stderr
213 is redirected to /dev/null; if you'd like to capture stderr you
214 can specify the ``DEBUG_FILE="file.txt"`` option to coccicheck. For
215 instance::
216
217 rm -f cocci.err
218 make coccicheck COCCI=scripts/coccinelle/free/kfree.cocci MODE=report DEBUG_FILE=cocci.err
219 cat cocci.err
220
221 You can use SPFLAGS to add debugging flags; for instance you may want to
222 add both ``--profile --show-trying`` to SPFLAGS when debugging. For example
223 you may want to use::
224
225 rm -f err.log
226 export COCCI=scripts/coccinelle/misc/irqf_oneshot.cocci
227 make coccicheck DEBUG_FILE="err.log" MODE=report SPFLAGS="--profile --show-trying" M=./drivers/mfd
228
229 err.log will now have the profiling information, while stdout will
230 provide some progress information as Coccinelle moves forward with
231 work.
232
233 NOTE:
234
235 DEBUG_FILE support is only supported when using coccinelle >= 1.0.2.
236
237 Currently, DEBUG_FILE support is only available to check folders, and
238 not single files. This is because checking a single file requires spatch
239 to be called twice leading to DEBUG_FILE being set both times to the same value,
240 giving rise to an error.
241
242 .cocciconfig support
243 --------------------
244
245 Coccinelle supports reading .cocciconfig for default Coccinelle options that
246 should be used every time spatch is spawned. The order of precedence for
247 variables for .cocciconfig is as follows:
248
249 - Your current user's home directory is processed first
250 - Your directory from which spatch is called is processed next
251 - The directory provided with the ``--dir`` option is processed last, if used
252
253 Since coccicheck runs through make, it naturally runs from the kernel
254 proper dir; as such the second rule above would be implied for picking up a
255 .cocciconfig when using ``make coccicheck``.
256
257 ``make coccicheck`` also supports using M= targets. If you do not supply
258 any M= target, it is assumed you want to target the entire kernel.
259 The kernel coccicheck script has::
260
261 if [ "$KBUILD_EXTMOD" = "" ] ; then
262 OPTIONS="--dir $srctree $COCCIINCLUDE"
263 else
264 OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
265 fi
266
267 KBUILD_EXTMOD is set when an explicit target with M= is used. For both cases
268 the spatch ``--dir`` argument is used, as such third rule applies when whether
269 M= is used or not, and when M= is used the target directory can have its own
270 .cocciconfig file. When M= is not passed as an argument to coccicheck the
271 target directory is the same as the directory from where spatch was called.
272
273 If not using the kernel's coccicheck target, keep the above precedence
274 order logic of .cocciconfig reading. If using the kernel's coccicheck target,
275 override any of the kernel's .coccicheck's settings using SPFLAGS.
276
277 We help Coccinelle when used against Linux with a set of sensible default
278 options for Linux with our own Linux .cocciconfig. This hints to coccinelle
279 that git can be used for ``git grep`` queries over coccigrep. A timeout of 200
280 seconds should suffice for now.
281
282 The options picked up by coccinelle when reading a .cocciconfig do not appear
283 as arguments to spatch processes running on your system. To confirm what
284 options will be used by Coccinelle run::
285
286 spatch --print-options-only
287
288 You can override with your own preferred index option by using SPFLAGS. Take
289 note that when there are conflicting options Coccinelle takes precedence for
290 the last options passed. Using .cocciconfig is possible to use idutils, however
291 given the order of precedence followed by Coccinelle, since the kernel now
292 carries its own .cocciconfig, you will need to use SPFLAGS to use idutils if
293 desired. See below section "Additional flags" for more details on how to use
294 idutils.
295
296 Additional flags
297 ----------------
298
299 Additional flags can be passed to spatch through the SPFLAGS
300 variable. This works as Coccinelle respects the last flags
301 given to it when options are in conflict. ::
302
303 make SPFLAGS=--use-glimpse coccicheck
304
305 Coccinelle supports idutils as well but requires coccinelle >= 1.0.6.
306 When no ID file is specified coccinelle assumes your ID database file
307 is in the file .id-utils.index on the top level of the kernel. Coccinelle
308 carries a script scripts/idutils_index.sh which creates the database with::
309
310 mkid -i C --output .id-utils.index
311
312 If you have another database filename you can also just symlink with this
313 name. ::
314
315 make SPFLAGS=--use-idutils coccicheck
316
317 Alternatively you can specify the database filename explicitly, for
318 instance::
319
320 make SPFLAGS="--use-idutils /full-path/to/ID" coccicheck
321
322 See ``spatch --help`` to learn more about spatch options.
323
324 Note that the ``--use-glimpse`` and ``--use-idutils`` options
325 require external tools for indexing the code. None of them is
326 thus active by default. However, by indexing the code with
327 one of these tools, and according to the cocci file used,
328 spatch could proceed the entire code base more quickly.
329
330 SmPL patch specific options
331 ---------------------------
332
333 SmPL patches can have their own requirements for options passed
334 to Coccinelle. SmPL patch-specific options can be provided by
335 providing them at the top of the SmPL patch, for instance::
336
337 // Options: --no-includes --include-headers
338
339 SmPL patch Coccinelle requirements
340 ----------------------------------
341
342 As Coccinelle features get added some more advanced SmPL patches
343 may require newer versions of Coccinelle. If an SmPL patch requires
344 a minimum version of Coccinelle, this can be specified as follows,
345 as an example if requiring at least Coccinelle >= 1.0.5::
346
347 // Requires: 1.0.5
348
349 Proposing new semantic patches
350 ------------------------------
351
352 New semantic patches can be proposed and submitted by kernel
353 developers. For sake of clarity, they should be organized in the
354 sub-directories of ``scripts/coccinelle/``.
355
356
357 Detailed description of the ``report`` mode
358 -------------------------------------------
359
360 ``report`` generates a list in the following format::
361
362 file:line:column-column: message
363
364 Example
365 ~~~~~~~
366
367 Running::
368
369 make coccicheck MODE=report COCCI=scripts/coccinelle/api/err_cast.cocci
370
371 will execute the following part of the SmPL script::
372
373 <smpl>
374 @r depends on !context && !patch && (org || report)@
375 expression x;
376 position p;
377 @@
378
379 ERR_PTR@p(PTR_ERR(x))
380
381 @script:python depends on report@
382 p << r.p;
383 x << r.x;
384 @@
385
386 msg="ERR_CAST can be used with %s" % (x)
387 coccilib.report.print_report(p[0], msg)
388 </smpl>
389
390 This SmPL excerpt generates entries on the standard output, as
391 illustrated below::
392
393 /home/user/linux/crypto/ctr.c:188:9-16: ERR_CAST can be used with alg
394 /home/user/linux/crypto/authenc.c:619:9-16: ERR_CAST can be used with auth
395 /home/user/linux/crypto/xts.c:227:9-16: ERR_CAST can be used with alg
396
397
398 Detailed description of the ``patch`` mode
399 ------------------------------------------
400
401 When the ``patch`` mode is available, it proposes a fix for each problem
402 identified.
403
404 Example
405 ~~~~~~~
406
407 Running::
408
409 make coccicheck MODE=patch COCCI=scripts/coccinelle/api/err_cast.cocci
410
411 will execute the following part of the SmPL script::
412
413 <smpl>
414 @ depends on !context && patch && !org && !report @
415 expression x;
416 @@
417
418 - ERR_PTR(PTR_ERR(x))
419 + ERR_CAST(x)
420 </smpl>
421
422 This SmPL excerpt generates patch hunks on the standard output, as
423 illustrated below::
424
425 diff -u -p a/crypto/ctr.c b/crypto/ctr.c
426 --- a/crypto/ctr.c 2010-05-26 10:49:38.000000000 +0200
427 +++ b/crypto/ctr.c 2010-06-03 23:44:49.000000000 +0200
428 @@ -185,7 +185,7 @@ static struct crypto_instance *crypto_ct
429 alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_CIPHER,
430 CRYPTO_ALG_TYPE_MASK);
431 if (IS_ERR(alg))
432 - return ERR_PTR(PTR_ERR(alg));
433 + return ERR_CAST(alg);
434
435 /* Block size must be >= 4 bytes. */
436 err = -EINVAL;
437
438 Detailed description of the ``context`` mode
439 --------------------------------------------
440
441 ``context`` highlights lines of interest and their context
442 in a diff-like style.
443
444 **NOTE**: The diff-like output generated is NOT an applicable patch. The
445 intent of the ``context`` mode is to highlight the important lines
446 (annotated with minus, ``-``) and gives some surrounding context
447 lines around. This output can be used with the diff mode of
448 Emacs to review the code.
449
450 Example
451 ~~~~~~~
452
453 Running::
454
455 make coccicheck MODE=context COCCI=scripts/coccinelle/api/err_cast.cocci
456
457 will execute the following part of the SmPL script::
458
459 <smpl>
460 @ depends on context && !patch && !org && !report@
461 expression x;
462 @@
463
464 * ERR_PTR(PTR_ERR(x))
465 </smpl>
466
467 This SmPL excerpt generates diff hunks on the standard output, as
468 illustrated below::
469
470 diff -u -p /home/user/linux/crypto/ctr.c /tmp/nothing
471 --- /home/user/linux/crypto/ctr.c 2010-05-26 10:49:38.000000000 +0200
472 +++ /tmp/nothing
473 @@ -185,7 +185,6 @@ static struct crypto_instance *crypto_ct
474 alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_CIPHER,
475 CRYPTO_ALG_TYPE_MASK);
476 if (IS_ERR(alg))
477 - return ERR_PTR(PTR_ERR(alg));
478
479 /* Block size must be >= 4 bytes. */
480 err = -EINVAL;
481
482 Detailed description of the ``org`` mode
483 ----------------------------------------
484
485 ``org`` generates a report in the Org mode format of Emacs.
486
487 Example
488 ~~~~~~~
489
490 Running::
491
492 make coccicheck MODE=org COCCI=scripts/coccinelle/api/err_cast.cocci
493
494 will execute the following part of the SmPL script::
495
496 <smpl>
497 @r depends on !context && !patch && (org || report)@
498 expression x;
499 position p;
500 @@
501
502 ERR_PTR@p(PTR_ERR(x))
503
504 @script:python depends on org@
505 p << r.p;
506 x << r.x;
507 @@
508
509 msg="ERR_CAST can be used with %s" % (x)
510 msg_safe=msg.replace("[","@(").replace("]",")")
511 coccilib.org.print_todo(p[0], msg_safe)
512 </smpl>
513
514 This SmPL excerpt generates Org entries on the standard output, as
515 illustrated below::
516
517 * TODO [[view:/home/user/linux/crypto/ctr.c::face=ovl-face1::linb=188::colb=9::cole=16][ERR_CAST can be used with alg]]
518 * TODO [[view:/home/user/linux/crypto/authenc.c::face=ovl-face1::linb=619::colb=9::cole=16][ERR_CAST can be used with auth]]
519 * TODO [[view:/home/user/linux/crypto/xts.c::face=ovl-face1::linb=227::colb=9::cole=16][ERR_CAST can be used with alg]]
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