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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
+
+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
+
+You can get the latest version released from the Coccinelle homepage at
+http://coccinelle.lip6.fr/
+
+Information and tips about Coccinelle are also provided on the wiki
+pages at http://cocci.ekstranet.diku.dk/wiki/doku.php
+
+Once you have it, run the following command::
+
+     	./configure
+        make
+
+as a regular user, and install it with::
+
+        sudo make install
+
+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.
+
+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 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, the return value of the ``make coccicheck``
+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
+following command may be used::
+
+    make C=1 CHECK="scripts/coccicheck"
+
+To check only newly edited code, use the value 2 for the C flag, i.e.::
+
+    make C=2 CHECK="scripts/coccicheck"
+
+In these modes, which works 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 instance
+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/arizona-irq.c
+
+err.log will now have the profiling information, while stdout will
+provide some progress information as Coccinelle moves forward with
+work.
+
+DEBUG_FILE support is only supported when using coccinelle >= 1.2.
+
+.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 defaults
+options for Linux with our own Linux .cocciconfig. This hints to coccinelle
+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
+at least a 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]]