492 lines
16 KiB
Plaintext
492 lines
16 KiB
Plaintext
.. Copyright 2010 Nicolas Palix <npalix@diku.dk>
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.. Copyright 2010 Julia Lawall <julia@diku.dk>
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.. Copyright 2010 Gilles Muller <Gilles.Muller@lip6.fr>
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.. highlight:: none
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Coccinelle
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==========
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Coccinelle is a tool for pattern matching and text transformation that has
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many uses in kernel development, including the application of complex,
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tree-wide patches and detection of problematic programming patterns.
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Getting Coccinelle
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-------------------
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The semantic patches included in the kernel use features and options
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which are provided by Coccinelle version 1.0.0-rc11 and above.
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Using earlier versions will fail as the option names used by
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the Coccinelle files and coccicheck have been updated.
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Coccinelle is available through the package manager
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of many distributions, e.g. :
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- Debian
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- Fedora
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- Ubuntu
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- OpenSUSE
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- Arch Linux
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- NetBSD
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- FreeBSD
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You can get the latest version released from the Coccinelle homepage at
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http://coccinelle.lip6.fr/
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Information and tips about Coccinelle are also provided on the wiki
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pages at http://cocci.ekstranet.diku.dk/wiki/doku.php
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Once you have it, run the following command::
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./configure
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make
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as a regular user, and install it with::
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sudo make install
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Supplemental documentation
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---------------------------
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For supplemental documentation refer to the wiki:
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https://bottest.wiki.kernel.org/coccicheck
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The wiki documentation always refers to the linux-next version of the script.
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Using Coccinelle on the Linux kernel
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------------------------------------
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A Coccinelle-specific target is defined in the top level
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Makefile. This target is named ``coccicheck`` and calls the ``coccicheck``
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front-end in the ``scripts`` directory.
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Four basic modes are defined: ``patch``, ``report``, ``context``, and
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``org``. The mode to use is specified by setting the MODE variable with
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``MODE=<mode>``.
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- ``patch`` proposes a fix, when possible.
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- ``report`` generates a list in the following format:
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file:line:column-column: message
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- ``context`` highlights lines of interest and their context in a
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diff-like style.Lines of interest are indicated with ``-``.
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- ``org`` generates a report in the Org mode format of Emacs.
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Note that not all semantic patches implement all modes. For easy use
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of Coccinelle, the default mode is "report".
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Two other modes provide some common combinations of these modes.
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- ``chain`` tries the previous modes in the order above until one succeeds.
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- ``rep+ctxt`` runs successively the report mode and the context mode.
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It should be used with the C option (described later)
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which checks the code on a file basis.
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Examples
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~~~~~~~~
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To make a report for every semantic patch, run the following command::
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make coccicheck MODE=report
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To produce patches, run::
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make coccicheck MODE=patch
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The coccicheck target applies every semantic patch available in the
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sub-directories of ``scripts/coccinelle`` to the entire Linux kernel.
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For each semantic patch, a commit message is proposed. It gives a
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description of the problem being checked by the semantic patch, and
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includes a reference to Coccinelle.
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As any static code analyzer, Coccinelle produces false
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positives. Thus, reports must be carefully checked, and patches
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reviewed.
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To enable verbose messages set the V= variable, for example::
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make coccicheck MODE=report V=1
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Coccinelle parallelization
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---------------------------
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By default, coccicheck tries to run as parallel as possible. To change
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the parallelism, set the J= variable. For example, to run across 4 CPUs::
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make coccicheck MODE=report J=4
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As of Coccinelle 1.0.2 Coccinelle uses Ocaml parmap for parallelization,
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if support for this is detected you will benefit from parmap parallelization.
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When parmap is enabled coccicheck will enable dynamic load balancing by using
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``--chunksize 1`` argument, this ensures we keep feeding threads with work
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one by one, so that we avoid the situation where most work gets done by only
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a few threads. With dynamic load balancing, if a thread finishes early we keep
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feeding it more work.
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When parmap is enabled, if an error occurs in Coccinelle, this error
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value is propagated back, the return value of the ``make coccicheck``
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captures this return value.
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Using Coccinelle with a single semantic patch
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---------------------------------------------
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The optional make variable COCCI can be used to check a single
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semantic patch. In that case, the variable must be initialized with
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the name of the semantic patch to apply.
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For instance::
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make coccicheck COCCI=<my_SP.cocci> MODE=patch
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or::
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make coccicheck COCCI=<my_SP.cocci> MODE=report
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Controlling Which Files are Processed by Coccinelle
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---------------------------------------------------
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By default the entire kernel source tree is checked.
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To apply Coccinelle to a specific directory, ``M=`` can be used.
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For example, to check drivers/net/wireless/ one may write::
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make coccicheck M=drivers/net/wireless/
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To apply Coccinelle on a file basis, instead of a directory basis, the
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following command may be used::
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make C=1 CHECK="scripts/coccicheck"
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To check only newly edited code, use the value 2 for the C flag, i.e.::
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make C=2 CHECK="scripts/coccicheck"
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In these modes, which works on a file basis, there is no information
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about semantic patches displayed, and no commit message proposed.
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This runs every semantic patch in scripts/coccinelle by default. The
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COCCI variable may additionally be used to only apply a single
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semantic patch as shown in the previous section.
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The "report" mode is the default. You can select another one with the
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MODE variable explained above.
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Debugging Coccinelle SmPL patches
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---------------------------------
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Using coccicheck is best as it provides in the spatch command line
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include options matching the options used when we compile the kernel.
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You can learn what these options are by using V=1, you could then
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manually run Coccinelle with debug options added.
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Alternatively you can debug running Coccinelle against SmPL patches
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by asking for stderr to be redirected to stderr, by default stderr
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is redirected to /dev/null, if you'd like to capture stderr you
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can specify the ``DEBUG_FILE="file.txt"`` option to coccicheck. For
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instance::
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rm -f cocci.err
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make coccicheck COCCI=scripts/coccinelle/free/kfree.cocci MODE=report DEBUG_FILE=cocci.err
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cat cocci.err
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You can use SPFLAGS to add debugging flags, for instance you may want to
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add both --profile --show-trying to SPFLAGS when debugging. For instance
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you may want to use::
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rm -f err.log
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export COCCI=scripts/coccinelle/misc/irqf_oneshot.cocci
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make coccicheck DEBUG_FILE="err.log" MODE=report SPFLAGS="--profile --show-trying" M=./drivers/mfd/arizona-irq.c
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err.log will now have the profiling information, while stdout will
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provide some progress information as Coccinelle moves forward with
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work.
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DEBUG_FILE support is only supported when using coccinelle >= 1.2.
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.cocciconfig support
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--------------------
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Coccinelle supports reading .cocciconfig for default Coccinelle options that
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should be used every time spatch is spawned, the order of precedence for
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variables for .cocciconfig is as follows:
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- Your current user's home directory is processed first
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- Your directory from which spatch is called is processed next
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- The directory provided with the --dir option is processed last, if used
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Since coccicheck runs through make, it naturally runs from the kernel
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proper dir, as such the second rule above would be implied for picking up a
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.cocciconfig when using ``make coccicheck``.
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``make coccicheck`` also supports using M= targets.If you do not supply
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any M= target, it is assumed you want to target the entire kernel.
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The kernel coccicheck script has::
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if [ "$KBUILD_EXTMOD" = "" ] ; then
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OPTIONS="--dir $srctree $COCCIINCLUDE"
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else
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OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
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fi
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KBUILD_EXTMOD is set when an explicit target with M= is used. For both cases
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the spatch --dir argument is used, as such third rule applies when whether M=
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is used or not, and when M= is used the target directory can have its own
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.cocciconfig file. When M= is not passed as an argument to coccicheck the
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target directory is the same as the directory from where spatch was called.
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If not using the kernel's coccicheck target, keep the above precedence
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order logic of .cocciconfig reading. If using the kernel's coccicheck target,
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override any of the kernel's .coccicheck's settings using SPFLAGS.
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We help Coccinelle when used against Linux with a set of sensible defaults
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options for Linux with our own Linux .cocciconfig. This hints to coccinelle
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git can be used for ``git grep`` queries over coccigrep. A timeout of 200
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seconds should suffice for now.
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The options picked up by coccinelle when reading a .cocciconfig do not appear
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as arguments to spatch processes running on your system, to confirm what
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options will be used by Coccinelle run::
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spatch --print-options-only
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You can override with your own preferred index option by using SPFLAGS. Take
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note that when there are conflicting options Coccinelle takes precedence for
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the last options passed. Using .cocciconfig is possible to use idutils, however
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given the order of precedence followed by Coccinelle, since the kernel now
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carries its own .cocciconfig, you will need to use SPFLAGS to use idutils if
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desired. See below section "Additional flags" for more details on how to use
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idutils.
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Additional flags
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----------------
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Additional flags can be passed to spatch through the SPFLAGS
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variable. This works as Coccinelle respects the last flags
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given to it when options are in conflict. ::
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make SPFLAGS=--use-glimpse coccicheck
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Coccinelle supports idutils as well but requires coccinelle >= 1.0.6.
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When no ID file is specified coccinelle assumes your ID database file
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is in the file .id-utils.index on the top level of the kernel, coccinelle
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carries a script scripts/idutils_index.sh which creates the database with::
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mkid -i C --output .id-utils.index
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If you have another database filename you can also just symlink with this
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name. ::
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make SPFLAGS=--use-idutils coccicheck
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Alternatively you can specify the database filename explicitly, for
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instance::
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make SPFLAGS="--use-idutils /full-path/to/ID" coccicheck
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See ``spatch --help`` to learn more about spatch options.
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Note that the ``--use-glimpse`` and ``--use-idutils`` options
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require external tools for indexing the code. None of them is
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thus active by default. However, by indexing the code with
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one of these tools, and according to the cocci file used,
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spatch could proceed the entire code base more quickly.
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SmPL patch specific options
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---------------------------
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SmPL patches can have their own requirements for options passed
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to Coccinelle. SmPL patch specific options can be provided by
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providing them at the top of the SmPL patch, for instance::
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// Options: --no-includes --include-headers
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SmPL patch Coccinelle requirements
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----------------------------------
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As Coccinelle features get added some more advanced SmPL patches
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may require newer versions of Coccinelle. If an SmPL patch requires
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at least a version of Coccinelle, this can be specified as follows,
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as an example if requiring at least Coccinelle >= 1.0.5::
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// Requires: 1.0.5
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Proposing new semantic patches
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-------------------------------
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New semantic patches can be proposed and submitted by kernel
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developers. For sake of clarity, they should be organized in the
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sub-directories of ``scripts/coccinelle/``.
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Detailed description of the ``report`` mode
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-------------------------------------------
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``report`` generates a list in the following format::
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file:line:column-column: message
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Example
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~~~~~~~
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Running::
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make coccicheck MODE=report COCCI=scripts/coccinelle/api/err_cast.cocci
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will execute the following part of the SmPL script::
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<smpl>
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@r depends on !context && !patch && (org || report)@
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expression x;
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position p;
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@@
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ERR_PTR@p(PTR_ERR(x))
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@script:python depends on report@
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p << r.p;
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x << r.x;
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@@
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msg="ERR_CAST can be used with %s" % (x)
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coccilib.report.print_report(p[0], msg)
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</smpl>
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This SmPL excerpt generates entries on the standard output, as
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illustrated below::
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/home/user/linux/crypto/ctr.c:188:9-16: ERR_CAST can be used with alg
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/home/user/linux/crypto/authenc.c:619:9-16: ERR_CAST can be used with auth
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/home/user/linux/crypto/xts.c:227:9-16: ERR_CAST can be used with alg
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Detailed description of the ``patch`` mode
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------------------------------------------
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When the ``patch`` mode is available, it proposes a fix for each problem
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identified.
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Example
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~~~~~~~
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Running::
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make coccicheck MODE=patch COCCI=scripts/coccinelle/api/err_cast.cocci
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will execute the following part of the SmPL script::
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<smpl>
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@ depends on !context && patch && !org && !report @
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expression x;
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@@
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- ERR_PTR(PTR_ERR(x))
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+ ERR_CAST(x)
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</smpl>
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This SmPL excerpt generates patch hunks on the standard output, as
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illustrated below::
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diff -u -p a/crypto/ctr.c b/crypto/ctr.c
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--- a/crypto/ctr.c 2010-05-26 10:49:38.000000000 +0200
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+++ b/crypto/ctr.c 2010-06-03 23:44:49.000000000 +0200
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@@ -185,7 +185,7 @@ static struct crypto_instance *crypto_ct
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alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_CIPHER,
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CRYPTO_ALG_TYPE_MASK);
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if (IS_ERR(alg))
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- return ERR_PTR(PTR_ERR(alg));
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+ return ERR_CAST(alg);
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/* Block size must be >= 4 bytes. */
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err = -EINVAL;
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Detailed description of the ``context`` mode
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--------------------------------------------
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``context`` highlights lines of interest and their context
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in a diff-like style.
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**NOTE**: The diff-like output generated is NOT an applicable patch. The
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intent of the ``context`` mode is to highlight the important lines
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(annotated with minus, ``-``) and gives some surrounding context
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lines around. This output can be used with the diff mode of
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Emacs to review the code.
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Example
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~~~~~~~
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Running::
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make coccicheck MODE=context COCCI=scripts/coccinelle/api/err_cast.cocci
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will execute the following part of the SmPL script::
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<smpl>
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@ depends on context && !patch && !org && !report@
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expression x;
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@@
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* ERR_PTR(PTR_ERR(x))
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</smpl>
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This SmPL excerpt generates diff hunks on the standard output, as
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illustrated below::
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diff -u -p /home/user/linux/crypto/ctr.c /tmp/nothing
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--- /home/user/linux/crypto/ctr.c 2010-05-26 10:49:38.000000000 +0200
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+++ /tmp/nothing
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@@ -185,7 +185,6 @@ static struct crypto_instance *crypto_ct
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alg = crypto_attr_alg(tb[1], CRYPTO_ALG_TYPE_CIPHER,
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CRYPTO_ALG_TYPE_MASK);
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if (IS_ERR(alg))
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- return ERR_PTR(PTR_ERR(alg));
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/* Block size must be >= 4 bytes. */
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err = -EINVAL;
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Detailed description of the ``org`` mode
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----------------------------------------
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``org`` generates a report in the Org mode format of Emacs.
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Example
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~~~~~~~
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Running::
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make coccicheck MODE=org COCCI=scripts/coccinelle/api/err_cast.cocci
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will execute the following part of the SmPL script::
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<smpl>
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@r depends on !context && !patch && (org || report)@
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expression x;
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position p;
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@@
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ERR_PTR@p(PTR_ERR(x))
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@script:python depends on org@
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p << r.p;
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x << r.x;
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@@
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msg="ERR_CAST can be used with %s" % (x)
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msg_safe=msg.replace("[","@(").replace("]",")")
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coccilib.org.print_todo(p[0], msg_safe)
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</smpl>
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This SmPL excerpt generates Org entries on the standard output, as
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illustrated below::
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* TODO [[view:/home/user/linux/crypto/ctr.c::face=ovl-face1::linb=188::colb=9::cole=16][ERR_CAST can be used with alg]]
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* TODO [[view:/home/user/linux/crypto/authenc.c::face=ovl-face1::linb=619::colb=9::cole=16][ERR_CAST can be used with auth]]
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* 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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