linux-next/Documentation/coccinelle.txt

Copyright 2010 Nicolas Palix <npalix@diku.dk>
Copyright 2010 Julia Lawall <julia@diku.dk>
Copyright 2010 Gilles Muller <Gilles.Muller@lip6.fr>


 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/

Once you have it, run the following command:

     	./configure
        make

as a regular user, and install it with

        sudo make install


 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: report, patch, context, and org. The mode to
use is specified by setting the MODE variable with 'MODE=<mode>'.

'report' generates a list in the following format:
  file:line:column-column: message

'patch' proposes a fix, when possible.

'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.

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
subdirectories of 'scripts/coccinelle' to the entire Linux kernel.

For each semantic patch, a changelog 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.


 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


 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
subdirectories 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/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/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/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/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]]