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 .. Copyright 2010 Nicolas Palix <npalix@diku.dk>
 .. Copyright 2010 Julia Lawall <julia@diku.dk>
 .. Copyright 2010 Gilles Muller <Gilles.Muller@lip6.fr>
 
 .. highlight:: none
 
 .. _devtools_coccinelle:
 
 Coccinelle
 ==========
 
 Coccinelle is a tool for pattern matching and text transformation that has
 many uses in kernel development, including the application of complex,
 tree-wide patches and detection of problematic programming patterns.
 
 Getting Coccinelle
 ------------------
 
 The semantic patches included in the kernel use features and options
 which are provided by Coccinelle version 1.0.0-rc11 and above.
 Using earlier versions will fail as the option names used by
 the Coccinelle files and coccicheck have been updated.
 
 Coccinelle is available through the package manager
 of many distributions, e.g. :
 
  - Debian
  - Fedora
  - Ubuntu
  - OpenSUSE
  - Arch Linux
  - NetBSD
  - FreeBSD
 
 Some distribution packages are obsolete and it is recommended
 to use the latest version released from the Coccinelle homepage at
 http://coccinelle.lip6.fr/
 
 Or from Github at:
 
 https://github.com/coccinelle/coccinelle
 
 Once you have it, run the following commands::
 
         ./autogen
         ./configure
         make
 
 as a regular user, and install it with::
 
         sudo make install
 
 More detailed installation instructions to build from source can be
 found at:
 
 https://github.com/coccinelle/coccinelle/blob/master/install.txt
 
 Supplemental documentation
 --------------------------
 
 For supplemental documentation refer to the wiki:
 
 https://bottest.wiki.kernel.org/coccicheck
 
 The wiki documentation always refers to the linux-next version of the script.
 
 For Semantic Patch Language(SmPL) grammar documentation refer to:
 
 https://coccinelle.gitlabpages.inria.fr/website/docs/main_grammar.html
 
 Using Coccinelle on the Linux kernel
 ------------------------------------
 
 A Coccinelle-specific target is defined in the top level
 Makefile. This target is named ``coccicheck`` and calls the ``coccicheck``
 front-end in the ``scripts`` directory.
 
 Four basic modes are defined: ``patch``, ``report``, ``context``, and
 ``org``. The mode to use is specified by setting the MODE variable with
 ``MODE=<mode>``.
 
 - ``patch`` proposes a fix, when possible.
 
 - ``report`` generates a list in the following format:
   file:line:column-column: message
 
 - ``context`` highlights lines of interest and their context in a
   diff-like style. Lines of interest are indicated with ``-``.
 
 - ``org`` generates a report in the Org mode format of Emacs.
 
 Note that not all semantic patches implement all modes. For easy use
 of Coccinelle, the default mode is "report".
 
 Two other modes provide some common combinations of these modes.
 
 - ``chain`` tries the previous modes in the order above until one succeeds.
 
 - ``rep+ctxt`` runs successively the report mode and the context mode.
   It should be used with the C option (described later)
   which checks the code on a file basis.
 
 Examples
 ~~~~~~~~
 
 To make a report for every semantic patch, run the following command::
 
                 make coccicheck MODE=report
 
 To produce patches, run::
 
                 make coccicheck MODE=patch
 
 
 The coccicheck target applies every semantic patch available in the
 sub-directories of ``scripts/coccinelle`` to the entire Linux kernel.
 
 For each semantic patch, a commit message is proposed.  It gives a
 description of the problem being checked by the semantic patch, and
 includes a reference to Coccinelle.
 
 As with any static code analyzer, Coccinelle produces false
 positives. Thus, reports must be carefully checked, and patches
 reviewed.
 
 To enable verbose messages set the V= variable, for example::
 
    make coccicheck MODE=report V=1
 
 Coccinelle parallelization
 --------------------------
 
 By default, coccicheck tries to run as parallel as possible. To change
 the parallelism, set the J= variable. For example, to run across 4 CPUs::
 
    make coccicheck MODE=report J=4
 
 As of Coccinelle 1.0.2 Coccinelle uses Ocaml parmap for parallelization;
 if support for this is detected you will benefit from parmap parallelization.
 
 When parmap is enabled coccicheck will enable dynamic load balancing by using
 ``--chunksize 1`` argument. This ensures we keep feeding threads with work
 one by one, so that we avoid the situation where most work gets done by only
 a few threads. With dynamic load balancing, if a thread finishes early we keep
 feeding it more work.
 
 When parmap is enabled, if an error occurs in Coccinelle, this error
 value is propagated back, and the return value of the ``make coccicheck``
 command captures this return value.
 
 Using Coccinelle with a single semantic patch
 ---------------------------------------------
 
 The optional make variable COCCI can be used to check a single
 semantic patch. In that case, the variable must be initialized with
 the name of the semantic patch to apply.
 
 For instance::
 
         make coccicheck COCCI=<my_SP.cocci> MODE=patch
 
 or::
 
         make coccicheck COCCI=<my_SP.cocci> MODE=report
 
 
 Controlling Which Files are Processed by Coccinelle
 ---------------------------------------------------
 
 By default the entire kernel source tree is checked.
 
 To apply Coccinelle to a specific directory, ``M=`` can be used.
 For example, to check drivers/net/wireless/ one may write::
 
     make coccicheck M=drivers/net/wireless/
 
 To apply Coccinelle on a file basis, instead of a directory basis, the
 C variable is used by the makefile to select which files to work with.
 This variable can be used to run scripts for the entire kernel, a
 specific directory, or for a single file.
 
 For example, to check drivers/bluetooth/bfusb.c, the value 1 is
 passed to the C variable to check files that make considers
 need to be compiled.::
 
     make C=1 CHECK=scripts/coccicheck drivers/bluetooth/bfusb.o
 
 The value 2 is passed to the C variable to check files regardless of
 whether they need to be compiled or not.::
 
     make C=2 CHECK=scripts/coccicheck drivers/bluetooth/bfusb.o
 
 In these modes, which work on a file basis, there is no information
 about semantic patches displayed, and no commit message proposed.
 
 This runs every semantic patch in scripts/coccinelle by default. The
 COCCI variable may additionally be used to only apply a single
 semantic patch as shown in the previous section.
 
 The "report" mode is the default. You can select another one with the
 MODE variable explained above.
 
 Debugging Coccinelle SmPL patches
 ---------------------------------
 
 Using coccicheck is best as it provides in the spatch command line
 include options matching the options used when we compile the kernel.
 You can learn what these options are by using V=1; you could then
 manually run Coccinelle with debug options added.
 
 Alternatively you can debug running Coccinelle against SmPL patches
 by asking for stderr to be redirected to stderr. By default stderr
 is redirected to /dev/null; if you'd like to capture stderr you
 can specify the ``DEBUG_FILE="file.txt"`` option to coccicheck. For
 instance::
 
     rm -f cocci.err
     make coccicheck COCCI=scripts/coccinelle/free/kfree.cocci MODE=report DEBUG_FILE=cocci.err
     cat cocci.err
 
 You can use SPFLAGS to add debugging flags; for instance you may want to
 add both --profile --show-trying to SPFLAGS when debugging. For example
 you may want to use::
 
     rm -f err.log
     export COCCI=scripts/coccinelle/misc/irqf_oneshot.cocci
     make coccicheck DEBUG_FILE="err.log" MODE=report SPFLAGS="--profile --show-trying" M=./drivers/mfd
 
 err.log will now have the profiling information, while stdout will
 provide some progress information as Coccinelle moves forward with
 work.
 
 NOTE:
 
 DEBUG_FILE support is only supported when using coccinelle >= 1.0.2.
 
 Currently, DEBUG_FILE support is only available to check folders, and
 not single files. This is because checking a single file requires spatch
 to be called twice leading to DEBUG_FILE being set both times to the same value,
 giving rise to an error.
 
 .cocciconfig support
 --------------------
 
 Coccinelle supports reading .cocciconfig for default Coccinelle options that
 should be used every time spatch is spawned. The order of precedence for
 variables for .cocciconfig is as follows:
 
 - Your current user's home directory is processed first
 - Your directory from which spatch is called is processed next
 - The directory provided with the --dir option is processed last, if used
 
 Since coccicheck runs through make, it naturally runs from the kernel
 proper dir; as such the second rule above would be implied for picking up a
 .cocciconfig when using ``make coccicheck``.
 
 ``make coccicheck`` also supports using M= targets. If you do not supply
 any M= target, it is assumed you want to target the entire kernel.
 The kernel coccicheck script has::
 
     if [ "$KBUILD_EXTMOD" = "" ] ; then
         OPTIONS="--dir $srctree $COCCIINCLUDE"
     else
         OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
     fi
 
 KBUILD_EXTMOD is set when an explicit target with M= is used. For both cases
 the spatch --dir argument is used, as such third rule applies when whether M=
 is used or not, and when M= is used the target directory can have its own
 .cocciconfig file. When M= is not passed as an argument to coccicheck the
 target directory is the same as the directory from where spatch was called.
 
 If not using the kernel's coccicheck target, keep the above precedence
 order logic of .cocciconfig reading. If using the kernel's coccicheck target,
 override any of the kernel's .coccicheck's settings using SPFLAGS.
 
 We help Coccinelle when used against Linux with a set of sensible default
 options for Linux with our own Linux .cocciconfig. This hints to coccinelle
 that git can be used for ``git grep`` queries over coccigrep. A timeout of 200
 seconds should suffice for now.
 
 The options picked up by coccinelle when reading a .cocciconfig do not appear
 as arguments to spatch processes running on your system. To confirm what
 options will be used by Coccinelle run::
 
       spatch --print-options-only
 
 You can override with your own preferred index option by using SPFLAGS. Take
 note that when there are conflicting options Coccinelle takes precedence for
 the last options passed. Using .cocciconfig is possible to use idutils, however
 given the order of precedence followed by Coccinelle, since the kernel now
 carries its own .cocciconfig, you will need to use SPFLAGS to use idutils if
 desired. See below section "Additional flags" for more details on how to use
 idutils.
 
 Additional flags
 ----------------
 
 Additional flags can be passed to spatch through the SPFLAGS
 variable. This works as Coccinelle respects the last flags
 given to it when options are in conflict. ::
 
     make SPFLAGS=--use-glimpse coccicheck
 
 Coccinelle supports idutils as well but requires coccinelle >= 1.0.6.
 When no ID file is specified coccinelle assumes your ID database file
 is in the file .id-utils.index on the top level of the kernel. Coccinelle
 carries a script scripts/idutils_index.sh which creates the database with::
 
     mkid -i C --output .id-utils.index
 
 If you have another database filename you can also just symlink with this
 name. ::
 
     make SPFLAGS=--use-idutils coccicheck
 
 Alternatively you can specify the database filename explicitly, for
 instance::
 
     make SPFLAGS="--use-idutils /full-path/to/ID" coccicheck
 
 See ``spatch --help`` to learn more about spatch options.
 
 Note that the ``--use-glimpse`` and ``--use-idutils`` options
 require external tools for indexing the code. None of them is
 thus active by default. However, by indexing the code with
 one of these tools, and according to the cocci file used,
 spatch could proceed the entire code base more quickly.
 
 SmPL patch specific options
 ---------------------------
 
 SmPL patches can have their own requirements for options passed
 to Coccinelle. SmPL patch-specific options can be provided by
 providing them at the top of the SmPL patch, for instance::
 
         // Options: --no-includes --include-headers
 
 SmPL patch Coccinelle requirements
 ----------------------------------
 
 As Coccinelle features get added some more advanced SmPL patches
 may require newer versions of Coccinelle. If an SmPL patch requires
 a minimum version of Coccinelle, this can be specified as follows,
 as an example if requiring at least Coccinelle >= 1.0.5::
 
         // Requires: 1.0.5
 
 Proposing new semantic patches
 ------------------------------
 
 New semantic patches can be proposed and submitted by kernel
 developers. For sake of clarity, they should be organized in the
 sub-directories of ``scripts/coccinelle/``.
 
 
 Detailed description of the ``report`` mode
 -------------------------------------------
 
 ``report`` generates a list in the following format::
 
   file:line:column-column: message
 
 Example
 ~~~~~~~
 
 Running::
 
         make coccicheck MODE=report COCCI=scripts/coccinelle/api/err_cast.cocci
 
 will execute the following part of the SmPL script::
 
    <smpl>
    @r depends on !context && !patch && (org || report)@
    expression x;
    position p;
    @@
 
      ERR_PTR@p(PTR_ERR(x))
 
    @script:python depends on report@
    p << r.p;
    x << r.x;
    @@
 
    msg="ERR_CAST can be used with %s" % (x)
    coccilib.report.print_report(p[0], msg)
    </smpl>
 
 This SmPL excerpt generates entries on the standard output, as
 illustrated below::
 
     /home/user/linux/crypto/ctr.c:188:9-16: ERR_CAST can be used with alg
     /home/user/linux/crypto/authenc.c:619:9-16: ERR_CAST can be used with auth
     /home/user/linux/crypto/xts.c:227:9-16: ERR_CAST can be used with alg
 
 
 Detailed description of the ``patch`` mode
 ------------------------------------------
 
 When the ``patch`` mode is available, it proposes a fix for each problem
 identified.
 
 Example
 ~~~~~~~
 
 Running::
 
         make coccicheck MODE=patch COCCI=scripts/coccinelle/api/err_cast.cocci
 
 will execute the following part of the SmPL script::
 
     <smpl>
     @ depends on !context && patch && !org && !report @
     expression x;
     @@
 
     - ERR_PTR(PTR_ERR(x))
     + ERR_CAST(x)
     </smpl>
 
 This SmPL excerpt generates patch hunks on the standard output, as
 illustrated below::
 
     diff -u -p a/crypto/ctr.c b/crypto/ctr.c
     --- a/crypto/ctr.c 2010-05-26 10:49:38.000000000 +0200
     +++ b/crypto/ctr.c 2010-06-03 23:44:49.000000000 +0200
     @@ -185,7 +185,7 @@ static struct crypto_instance *crypto_ct
         alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_CIPHER,
                                   CRYPTO_ALG_TYPE_MASK);
         if (IS_ERR(alg))
     -           return ERR_PTR(PTR_ERR(alg));
     +           return ERR_CAST(alg);
 
         /* Block size must be >= 4 bytes. */
         err = -EINVAL;
 
 Detailed description of the ``context`` mode
 --------------------------------------------
 
 ``context`` highlights lines of interest and their context
 in a diff-like style.
 
       **NOTE**: The diff-like output generated is NOT an applicable patch. The
       intent of the ``context`` mode is to highlight the important lines
       (annotated with minus, ``-``) and gives some surrounding context
       lines around. This output can be used with the diff mode of
       Emacs to review the code.
 
 Example
 ~~~~~~~
 
 Running::
 
         make coccicheck MODE=context COCCI=scripts/coccinelle/api/err_cast.cocci
 
 will execute the following part of the SmPL script::
 
     <smpl>
     @ depends on context && !patch && !org && !report@
     expression x;
     @@
 
     * ERR_PTR(PTR_ERR(x))
     </smpl>
 
 This SmPL excerpt generates diff hunks on the standard output, as
 illustrated below::
 
     diff -u -p /home/user/linux/crypto/ctr.c /tmp/nothing
     --- /home/user/linux/crypto/ctr.c   2010-05-26 10:49:38.000000000 +0200
     +++ /tmp/nothing
     @@ -185,7 +185,6 @@ static struct crypto_instance *crypto_ct
         alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_CIPHER,
                                   CRYPTO_ALG_TYPE_MASK);
         if (IS_ERR(alg))
     -           return ERR_PTR(PTR_ERR(alg));
 
         /* Block size must be >= 4 bytes. */
         err = -EINVAL;
 
 Detailed description of the ``org`` mode
 ----------------------------------------
 
 ``org`` generates a report in the Org mode format of Emacs.
 
 Example
 ~~~~~~~
 
 Running::
 
         make coccicheck MODE=org COCCI=scripts/coccinelle/api/err_cast.cocci
 
 will execute the following part of the SmPL script::
 
     <smpl>
     @r depends on !context && !patch && (org || report)@
     expression x;
     position p;
     @@
 
       ERR_PTR@p(PTR_ERR(x))
 
     @script:python depends on org@
     p << r.p;
     x << r.x;
     @@
 
     msg="ERR_CAST can be used with %s" % (x)
     msg_safe=msg.replace("[","@(").replace("]",")")
     coccilib.org.print_todo(p[0], msg_safe)
     </smpl>
 
 This SmPL excerpt generates Org entries on the standard output, as
 illustrated below::
 
     * TODO [[view:/home/user/linux/crypto/ctr.c::face=ovl-face1::linb=188::colb=9::cole=16][ERR_CAST can be used with alg]]
     * TODO [[view:/home/user/linux/crypto/authenc.c::face=ovl-face1::linb=619::colb=9::cole=16][ERR_CAST can be used with auth]]
     * 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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