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>
7 .. _devtools_coccinelle:
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.
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.
24 Coccinelle is available through the package manager
25 of many distributions, e.g. :
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/
41 https://github.com/coccinelle/coccinelle
43 Once you have it, run the following commands::
49 as a regular user, and install it with::
53 More detailed installation instructions to build from source can be
56 https://github.com/coccinelle/coccinelle/blob/master/install.txt
58 Supplemental documentation
59 --------------------------
61 For supplemental documentation refer to the wiki:
63 https://bottest.wiki.kernel.org/coccicheck
65 The wiki documentation always refers to the linux-next version of the script.
67 For Semantic Patch Language(SmPL) grammar documentation refer to:
69 http://coccinelle.lip6.fr/documentation.php
71 Using Coccinelle on the Linux kernel
72 ------------------------------------
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.
78 Four basic modes are defined: ``patch``, ``report``, ``context``, and
79 ``org``. The mode to use is specified by setting the MODE variable with
82 - ``patch`` proposes a fix, when possible.
84 - ``report`` generates a list in the following format:
85 file:line:column-column: message
87 - ``context`` highlights lines of interest and their context in a
88 diff-like style. Lines of interest are indicated with ``-``.
90 - ``org`` generates a report in the Org mode format of Emacs.
92 Note that not all semantic patches implement all modes. For easy use
93 of Coccinelle, the default mode is "report".
95 Two other modes provide some common combinations of these modes.
97 - ``chain`` tries the previous modes in the order above until one succeeds.
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.
106 To make a report for every semantic patch, run the following command::
108 make coccicheck MODE=report
110 To produce patches, run::
112 make coccicheck MODE=patch
115 The coccicheck target applies every semantic patch available in the
116 sub-directories of ``scripts/coccinelle`` to the entire Linux kernel.
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.
122 As with any static code analyzer, Coccinelle produces false
123 positives. Thus, reports must be carefully checked, and patches
126 To enable verbose messages set the V= variable, for example::
128 make coccicheck MODE=report V=1
130 Coccinelle parallelization
131 --------------------------
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::
136 make coccicheck MODE=report J=4
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.
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.
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.
151 Using Coccinelle with a single semantic patch
152 ---------------------------------------------
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.
160 make coccicheck COCCI=<my_SP.cocci> MODE=patch
164 make coccicheck COCCI=<my_SP.cocci> MODE=report
167 Controlling Which Files are Processed by Coccinelle
168 ---------------------------------------------------
170 By default the entire kernel source tree is checked.
172 To apply Coccinelle to a specific directory, ``M=`` can be used.
173 For example, to check drivers/net/wireless/ one may write::
175 make coccicheck M=drivers/net/wireless/
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.
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.::
186 make C=1 CHECK=scripts/coccicheck drivers/bluetooth/bfusb.o
188 The value 2 is passed to the C variable to check files regardless of
189 whether they need to be compiled or not.::
191 make C=2 CHECK=scripts/coccicheck drivers/bluetooth/bfusb.o
193 In these modes, which work on a file basis, there is no information
194 about semantic patches displayed, and no commit message proposed.
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.
200 The "report" mode is the default. You can select another one with the
201 MODE variable explained above.
203 Debugging Coccinelle SmPL patches
204 ---------------------------------
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.
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
218 make coccicheck COCCI=scripts/coccinelle/free/kfree.cocci MODE=report DEBUG_FILE=cocci.err
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::
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/arizona-irq.c
229 err.log will now have the profiling information, while stdout will
230 provide some progress information as Coccinelle moves forward with
233 DEBUG_FILE support is only supported when using coccinelle >= 1.0.2.
238 Coccinelle supports reading .cocciconfig for default Coccinelle options that
239 should be used every time spatch is spawned. The order of precedence for
240 variables for .cocciconfig is as follows:
242 - Your current user's home directory is processed first
243 - Your directory from which spatch is called is processed next
244 - The directory provided with the --dir option is processed last, if used
246 Since coccicheck runs through make, it naturally runs from the kernel
247 proper dir; as such the second rule above would be implied for picking up a
248 .cocciconfig when using ``make coccicheck``.
250 ``make coccicheck`` also supports using M= targets. If you do not supply
251 any M= target, it is assumed you want to target the entire kernel.
252 The kernel coccicheck script has::
254 if [ "$KBUILD_EXTMOD" = "" ] ; then
255 OPTIONS="--dir $srctree $COCCIINCLUDE"
257 OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
260 KBUILD_EXTMOD is set when an explicit target with M= is used. For both cases
261 the spatch --dir argument is used, as such third rule applies when whether M=
262 is used or not, and when M= is used the target directory can have its own
263 .cocciconfig file. When M= is not passed as an argument to coccicheck the
264 target directory is the same as the directory from where spatch was called.
266 If not using the kernel's coccicheck target, keep the above precedence
267 order logic of .cocciconfig reading. If using the kernel's coccicheck target,
268 override any of the kernel's .coccicheck's settings using SPFLAGS.
270 We help Coccinelle when used against Linux with a set of sensible default
271 options for Linux with our own Linux .cocciconfig. This hints to coccinelle
272 that git can be used for ``git grep`` queries over coccigrep. A timeout of 200
273 seconds should suffice for now.
275 The options picked up by coccinelle when reading a .cocciconfig do not appear
276 as arguments to spatch processes running on your system. To confirm what
277 options will be used by Coccinelle run::
279 spatch --print-options-only
281 You can override with your own preferred index option by using SPFLAGS. Take
282 note that when there are conflicting options Coccinelle takes precedence for
283 the last options passed. Using .cocciconfig is possible to use idutils, however
284 given the order of precedence followed by Coccinelle, since the kernel now
285 carries its own .cocciconfig, you will need to use SPFLAGS to use idutils if
286 desired. See below section "Additional flags" for more details on how to use
292 Additional flags can be passed to spatch through the SPFLAGS
293 variable. This works as Coccinelle respects the last flags
294 given to it when options are in conflict. ::
296 make SPFLAGS=--use-glimpse coccicheck
298 Coccinelle supports idutils as well but requires coccinelle >= 1.0.6.
299 When no ID file is specified coccinelle assumes your ID database file
300 is in the file .id-utils.index on the top level of the kernel. Coccinelle
301 carries a script scripts/idutils_index.sh which creates the database with::
303 mkid -i C --output .id-utils.index
305 If you have another database filename you can also just symlink with this
308 make SPFLAGS=--use-idutils coccicheck
310 Alternatively you can specify the database filename explicitly, for
313 make SPFLAGS="--use-idutils /full-path/to/ID" coccicheck
315 See ``spatch --help`` to learn more about spatch options.
317 Note that the ``--use-glimpse`` and ``--use-idutils`` options
318 require external tools for indexing the code. None of them is
319 thus active by default. However, by indexing the code with
320 one of these tools, and according to the cocci file used,
321 spatch could proceed the entire code base more quickly.
323 SmPL patch specific options
324 ---------------------------
326 SmPL patches can have their own requirements for options passed
327 to Coccinelle. SmPL patch-specific options can be provided by
328 providing them at the top of the SmPL patch, for instance::
330 // Options: --no-includes --include-headers
332 SmPL patch Coccinelle requirements
333 ----------------------------------
335 As Coccinelle features get added some more advanced SmPL patches
336 may require newer versions of Coccinelle. If an SmPL patch requires
337 a minimum version of Coccinelle, this can be specified as follows,
338 as an example if requiring at least Coccinelle >= 1.0.5::
342 Proposing new semantic patches
343 ------------------------------
345 New semantic patches can be proposed and submitted by kernel
346 developers. For sake of clarity, they should be organized in the
347 sub-directories of ``scripts/coccinelle/``.
350 Detailed description of the ``report`` mode
351 -------------------------------------------
353 ``report`` generates a list in the following format::
355 file:line:column-column: message
362 make coccicheck MODE=report COCCI=scripts/coccinelle/api/err_cast.cocci
364 will execute the following part of the SmPL script::
367 @r depends on !context && !patch && (org || report)@
372 ERR_PTR@p(PTR_ERR(x))
374 @script:python depends on report@
379 msg="ERR_CAST can be used with %s" % (x)
380 coccilib.report.print_report(p[0], msg)
383 This SmPL excerpt generates entries on the standard output, as
386 /home/user/linux/crypto/ctr.c:188:9-16: ERR_CAST can be used with alg
387 /home/user/linux/crypto/authenc.c:619:9-16: ERR_CAST can be used with auth
388 /home/user/linux/crypto/xts.c:227:9-16: ERR_CAST can be used with alg
391 Detailed description of the ``patch`` mode
392 ------------------------------------------
394 When the ``patch`` mode is available, it proposes a fix for each problem
402 make coccicheck MODE=patch COCCI=scripts/coccinelle/api/err_cast.cocci
404 will execute the following part of the SmPL script::
407 @ depends on !context && patch && !org && !report @
411 - ERR_PTR(PTR_ERR(x))
415 This SmPL excerpt generates patch hunks on the standard output, as
418 diff -u -p a/crypto/ctr.c b/crypto/ctr.c
419 --- a/crypto/ctr.c 2010-05-26 10:49:38.000000000 +0200
420 +++ b/crypto/ctr.c 2010-06-03 23:44:49.000000000 +0200
421 @@ -185,7 +185,7 @@ static struct crypto_instance *crypto_ct
422 alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_CIPHER,
423 CRYPTO_ALG_TYPE_MASK);
425 - return ERR_PTR(PTR_ERR(alg));
426 + return ERR_CAST(alg);
428 /* Block size must be >= 4 bytes. */
431 Detailed description of the ``context`` mode
432 --------------------------------------------
434 ``context`` highlights lines of interest and their context
435 in a diff-like style.
437 **NOTE**: The diff-like output generated is NOT an applicable patch. The
438 intent of the ``context`` mode is to highlight the important lines
439 (annotated with minus, ``-``) and gives some surrounding context
440 lines around. This output can be used with the diff mode of
441 Emacs to review the code.
448 make coccicheck MODE=context COCCI=scripts/coccinelle/api/err_cast.cocci
450 will execute the following part of the SmPL script::
453 @ depends on context && !patch && !org && !report@
457 * ERR_PTR(PTR_ERR(x))
460 This SmPL excerpt generates diff hunks on the standard output, as
463 diff -u -p /home/user/linux/crypto/ctr.c /tmp/nothing
464 --- /home/user/linux/crypto/ctr.c 2010-05-26 10:49:38.000000000 +0200
466 @@ -185,7 +185,6 @@ static struct crypto_instance *crypto_ct
467 alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_CIPHER,
468 CRYPTO_ALG_TYPE_MASK);
470 - return ERR_PTR(PTR_ERR(alg));
472 /* Block size must be >= 4 bytes. */
475 Detailed description of the ``org`` mode
476 ----------------------------------------
478 ``org`` generates a report in the Org mode format of Emacs.
485 make coccicheck MODE=org COCCI=scripts/coccinelle/api/err_cast.cocci
487 will execute the following part of the SmPL script::
490 @r depends on !context && !patch && (org || report)@
495 ERR_PTR@p(PTR_ERR(x))
497 @script:python depends on org@
502 msg="ERR_CAST can be used with %s" % (x)
503 msg_safe=msg.replace("[","@(").replace("]",")")
504 coccilib.org.print_todo(p[0], msg_safe)
507 This SmPL excerpt generates Org entries on the standard output, as
510 * TODO [[view:/home/user/linux/crypto/ctr.c::face=ovl-face1::linb=188::colb=9::cole=16][ERR_CAST can be used with alg]]
511 * TODO [[view:/home/user/linux/crypto/authenc.c::face=ovl-face1::linb=619::colb=9::cole=16][ERR_CAST can be used with auth]]
512 * TODO [[view:/home/user/linux/crypto/xts.c::face=ovl-face1::linb=227::colb=9::cole=16][ERR_CAST can be used with alg]]