kernel / Documentation / coccinelle.txt

Copyright 2010 Nicolas Palix <[e-mail]>
Copyright 2010 Julia Lawall <[e-mail]>
Copyright 2010 Gilles Muller <[e-mail]>


 Getting Coccinelle
~~~~~~~~~~~~~~~~~~~~

The semantic patches included in the kernel use the 'virtual rule'
feature which was introduced in Coccinelle version 0.1.11.

Coccinelle (>=0.2.0) is available through the package manager
of many distributions, e.g. :

 - Debian (>=squeeze)
 - Fedora (>=13)
 - Ubuntu (>=10.04 Lucid Lynx)
 - 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

The semantic patches in the kernel will work best with Coccinelle version
0.2.4 or later.  Using earlier versions may incur some parse errors in the
semantic patch code, but any results that are obtained should still be
correct.

 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 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 "chain" which tries the previous
modes in the order above until one succeeds.

To make a report for every semantic patch, run the following command:

	make coccicheck MODE=report

NB: The 'report' mode is the default one.

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


 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"

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 "chain" mode is the default. You can select another one with the
MODE variable explained above.

In this mode, there is no information about semantic patches
displayed, and no commit message proposed.


 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]]