Re: [Cocci] Re: status of constification

[Julia Lawall <julia@diku.dk>]

On Tue, 9 Nov 2010, Emese Revfy wrote:

> 
> > Hi,
> >
> > So, I'm trying to come up to speed on what's still outstanding in the
> > effort to constify function pointers. I saw patches from Emese Revfy
> > go in, and I saw Lionel Debroux's recent patches. What already-created
> > work still needs attention? I know there's more code to be written,
> > but I'm trying to find any patches that have already been written but
> > have not gone upstream yet.
> Hi, 
> 
> I will gladly break up my current patch for the next -rc by structure
> type or maintainer (some preferred it one way or the other) and send
> it in some time next week so that you can handle the upstream submission
> process (I will continue to maintain my patch in grsecurity).
> 
> There are many structures that can be constified, you can use the following
> command to find most of them (use it on an allyesconfig kernel preferably):
> 
> grep _ops System.map |grep -Ewi 'b|d' | awk '{print $3}' | \
> while read i ; do cscope -d -L -1 $i | grep -E "struct[ \t]*([^ ]*)[ \t]*" \
> --color=none -o | awk '{print $2}' ; done |sort -u
> 
> Also there are always new instances of structures going in that should have
> been constified.
> 
> I tried to automate the whole process with Coccinelle but I abandoned it
> because Coccinelle didn't support recursive header file inclusion at the time.
> If someone feels like fixing Coccinelle then I would quickly finish my script
> (it has a few bugs because I could never test it for real), but see the end
> of the mail for the current version. I think it would be a good idea because
> it would take a few hours only to generate a constification patch for a new
> kernel. One thing that probably cannot be automated with Coccinelle is that
> once the script determines that a given structure cannot be constified, it
> cannot undo already emitted patches for the given structure so it must be
> cleaned up by post processing script.

What would the right approach be?  It is not obvious to find 100% of the 
header files, because some of them depend on information in Makefiles.  
You can use that information by running the preprocessor on Coccinelle 
first, but then the result is only useful for finding files that need 
changing, but not actually making the changes because Coccinelle does not 
relate the preprocessed code back to the original code.  But if you run 
the preprocessor, you only get information for your current configuration, 
which is probably not what you want.

Coccinelle could certainly get a new option -really_all_includes, or 
something like that, that would recursively include among what it can find 
and what has not been included already.  Would that be what is wanted?

I guess that in practice the includes are only being used for type 
information?  Wouldn't it be safe to run the semantic patch based on the 
includes that are available?

julia

> 
> --
> Emese
> 
> 
> // spatch.opt -sp_file $1 -include_headers -local_includes -all_includes -I "include/" -dir $2
> 
> @initialize:python@
> noconst = []
> 
> @stc@
> identifier idtype, y;
> type t;
> position p;
> @@
> struct idtype {
> 	...
> 	t (*y)(...);@p
> 	...
> };
> 
> @notjustfp@
> identifier stc.idtype, y;
> type t;
> position p != stc.p;
> @@
> struct idtype {
> 	...
> 	t y;@p
> 	...
> };
> 
> @script:python depends on notjustfp@
> @@
> cocci.include_match(False)
> 
> @variable@
> identifier stc.idtype, idvariant, id;
> @@
> (
> 	struct idtype idvariant = {
> 		...
> 	};
> |
> 	struct idtype idvariant;
> |
> 	struct idtype *idvariant;
> |
> 	struct id {
> 		...
> 		struct idtype idvariant;
> 		...
> 	};
> )
> 
> @script:python@
> y << variable.idvariant;
> @@
> if y in noconst:
> 	cocci.include_match(False)
> 
> @alreadyconst@
> identifier stc.idtype, variable.idvariant, id;
> @@
> (
> 	const struct idtype idvariant;
> |
> 	const struct idtype idvariant = {
> 		...
> 	};
> |
> 	const struct idtype *idvariant;
> |
> 	struct id {
> 		...
> 		const struct idtype idvariant;
> 		...
> 	};
> )
> 
> @script:python depends on alreadyconst@
> @@
> cocci.include_match(False)
> 
> @fn_declaration@
> identifier stc.idtype, variable.idvariant, fn;
> type t;
> @@
> t fn(struct idtype *idvariant);
> 
> @fn_definition@
> identifier stc.idtype, variable.idvariant, fn;
> type t;
> @@
> t fn(struct idtype *idvariant)
> {
> 	...
> }
> 
> // TODO: handle var.field1.field2, var->field1->field2
> @assignement@
> identifier variable.idvariant, x, idptr;
> @@
> (
> 	idvariant.x = ...;
> |
> 	idvariant->x = ...;
> |
> 	idptr = &idvariant;
> 	...
> 	idptr->x = ...;
> |
> 	memcpy(&idvariant, ...);
> |
> 	memcpy(idvariant.x, ...);
> |
> 	memcpy(idvariant->x, ...);
> |
> 	idvariant = kzalloc(...);
> |
> 	idvariant = kmalloc(...);
> )
> 
> @script:python depends on assignement@
> x << stc.idtype;
> y << variable.idvariant;
> @@
> print "Cannot be const: %s-%s" % (x, y)
> noconst.append(y)
> cocci.include_match(False)
> 
> @depends on stc && !fn_declaration && !fn_definition@
> identifier stc.idtype, variable.idvariant, id;
> @@
> (
> -struct idtype idvariant = {
> +const struct idtype idvariant = {
> 		...
>  };
> |
> -struct idtype idvariant;
> +const struct idtype idvariant;
> |
> -struct idtype *idvariant;
> +const struct idtype *idvariant;
> |
> -struct idtype *idvariant = NULL;
> +const struct idtype *idvariant = NULL;
> |
> struct id {
> ...
> -struct idtype idvariant;
> +const struct idtype idvariant;
> ...
>  };
> )
> 
> @depends on stc && fn_declaration && !fn_definition@
> identifier stc.idtype, variable.idvariant, fn_declaration.fn;
> type fn_declaration.t;
> @@
> t fn(
> -struct idtype *idvariant
> +const struct idtype *idvariant
>  );
> 
> @depends on stc && !fn_declaration && fn_definition@
> identifier stc.idtype, variable.idvariant, fn_definition.fn;
> type fn_definition.t;
> @@
> t fn(
> -struct idtype *idvariant
> +const struct idtype *idvariant
>  )
>  {
>  	...
>  }
> 
>