Getting Coccinelle¶

The semantic patches included in the kernel use features and optionswhich are provided by Coccinelle version 1.0.0-rc11 and above.Using earlier versions will fail as the option names used bythe Coccinelle files and coccicheck have been updated.

Coccinelle is available through the package managerof many distributions, e.g. :

• Debian

• Fedora

• Ubuntu

• OpenSUSE

• Arch Linux

• NetBSD

• FreeBSD

Some distribution packages are obsolete and it is recommendedto use the latest version released from the Coccinelle homepage athttp://coccinelle.lip6.fr/

Or from Github at:

https://github.com/coccinelle/coccinelle

Once you have it, run the following commands:

./autogen./configuremake

as a regular user, and install it with:

sudo make install

More detailed installation instructions to build from source can befound 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 levelMakefile. This target is namedcoccicheck and calls thecoccicheckfront-end in thescripts directory.

Four basic modes are defined:patch,report,context, andorg. The mode to use is specified by setting the MODE variable withMODE=<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 adiff-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 useof 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.

make coccicheck MODE=report

make coccicheck MODE=patch

make coccicheck MODE=report V=1

Coccinelle parallelization¶

By default, coccicheck tries to run as parallel as possible. To changethe 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--chunksize1 argument. This ensures we keep feeding threads with workone by one, so that we avoid the situation where most work gets done by onlya few threads. With dynamic load balancing, if a thread finishes early we keepfeeding it more work.

When parmap is enabled, if an error occurs in Coccinelle, this errorvalue is propagated back, and the return value of themakecoccicheckcommand captures this return value.

Using Coccinelle with a single semantic patch¶

The optional make variable COCCI can be used to check a singlesemantic patch. In that case, the variable must be initialized withthe 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, theC 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, aspecific directory, or for a single file.

For example, to check drivers/bluetooth/bfusb.c, the value 1 ispassed to the C variable to check files that make considersneed 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 ofwhether 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 informationabout semantic patches displayed, and no commit message proposed.

This runs every semantic patch in scripts/coccinelle by default. TheCOCCI variable may additionally be used to only apply a singlesemantic patch as shown in the previous section.

The “report” mode is the default. You can select another one with theMODE variable explained above.

Debugging Coccinelle SmPL patches¶

Using coccicheck is best as it provides in the spatch command lineinclude options matching the options used when we compile the kernel.You can learn what these options are by using V=1; you could thenmanually run Coccinelle with debug options added.

Alternatively you can debug running Coccinelle against SmPL patchesby asking for stderr to be redirected to stderr. By default stderris redirected to /dev/null; if you’d like to capture stderr youcan specify theDEBUG_FILE="file.txt" option to coccicheck. Forinstance:

rm -f cocci.errmake coccicheck COCCI=scripts/coccinelle/free/kfree.cocci MODE=report DEBUG_FILE=cocci.errcat cocci.err

You can use SPFLAGS to add debugging flags; for instance you may want toadd both--profile--show-trying to SPFLAGS when debugging. For exampleyou may want to use:

rm -f err.logexport COCCI=scripts/coccinelle/misc/irqf_oneshot.coccimake coccicheck DEBUG_FILE="err.log" MODE=report SPFLAGS="--profile --show-trying" M=./drivers/mfd

err.log will now have the profiling information, while stdout willprovide some progress information as Coccinelle moves forward withwork.

NOTE:

DEBUG_FILE support is only supported when using coccinelle >= 1.0.2.

Currently, DEBUG_FILE support is only available to check folders, andnot single files. This is because checking a single file requires spatchto 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 thatshould be used every time spatch is spawned. The order of precedence forvariables 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

makecoccicheck also supports using M= targets. If you do not supplyany M= target, it is assumed you want to target the entire kernel.The kernel coccicheck script has:

OPTIONS="--dir $srcroot $COCCIINCLUDE"

Here, $srcroot refers to the source directory of the target: it points to theexternal module’s source directory when M= used, and otherwise, to the kernelsource directory. The third rule ensures the spatch reads the .cocciconfig fromthe target directory, allowing external modules to have their own .cocciconfigfile.

If not using the kernel’s coccicheck target, keep the above precedenceorder 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 defaultoptions for Linux with our own Linux .cocciconfig. This hints to coccinellethat git can be used forgitgrep queries over coccigrep. A timeout of 200seconds should suffice for now.

The options picked up by coccinelle when reading a .cocciconfig do not appearas arguments to spatch processes running on your system. To confirm whatoptions will be used by Coccinelle run:

spatch --print-options-only

You can override with your own preferred index option by using SPFLAGS. Takenote that when there are conflicting options Coccinelle takes precedence forthe last options passed. Using .cocciconfig is possible to use idutils, howevergiven the order of precedence followed by Coccinelle, since the kernel nowcarries its own .cocciconfig, you will need to use SPFLAGS to use idutils ifdesired. See below section “Additional flags” for more details on how to useidutils.

Additional flags¶

Additional flags can be passed to spatch through the SPFLAGSvariable. This works as Coccinelle respects the last flagsgiven 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 fileis in the file .id-utils.index on the top level of the kernel. Coccinellecarries 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 thisname.

make SPFLAGS=--use-idutils coccicheck

Alternatively you can specify the database filename explicitly, forinstance:

make SPFLAGS="--use-idutils /full-path/to/ID" coccicheck

Seespatch--help to learn more about spatch options.

Note that the--use-glimpse and--use-idutils optionsrequire external tools for indexing the code. None of them isthus active by default. However, by indexing the code withone 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 passedto Coccinelle. SmPL patch-specific options can be provided byproviding 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 patchesmay require newer versions of Coccinelle. If an SmPL patch requiresa 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 kerneldevelopers. For sake of clarity, they should be organized in thesub-directories ofscripts/coccinelle/.

Detailed description of thereport mode¶

report generates a list in the following format:

file:line:column-column: message

make coccicheck MODE=report COCCI=scripts/coccinelle/api/err_cast.cocci

<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>

/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 thepatch mode¶

When thepatch mode is available, it proposes a fix for each problemidentified.

make coccicheck MODE=patch COCCI=scripts/coccinelle/api/err_cast.cocci

<smpl>@ depends on !context && patch && !org && !report @expression x;@@- ERR_PTR(PTR_ERR(x))+ ERR_CAST(x)</smpl>

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 thecontext mode¶

context highlights lines of interest and their contextin a diff-like style.

NOTE: The diff-like output generated is NOT an applicable patch. Theintent of thecontext mode is to highlight the important lines(annotated with minus,-) and gives some surrounding contextlines around. This output can be used with the diff mode ofEmacs to review the code.

make coccicheck MODE=context COCCI=scripts/coccinelle/api/err_cast.cocci

<smpl>@ depends on context && !patch && !org && !report@expression x;@@* ERR_PTR(PTR_ERR(x))</smpl>

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 theorg mode¶

org generates a report in the Org mode format of Emacs.

make coccicheck MODE=org COCCI=scripts/coccinelle/api/err_cast.cocci

<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>

* 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]]