[Cocci] Patching const char * constants

[Rob Hoelz]

Hi Coccinelle community,

I just discovered Coccinelle a few days ago, and already my mind is reeling with the possibilities.
I'm doing some work porting the Claws Mail mail client to GTK3, and I think Coccinelle would be a
great tool to use to accomplish this task.

One of the thing I'm trying to use Coccinelle to do is to detect and patch string concatenation via

...
GTK_STOCK_NO, "+" GTK_STOCK_YES, NULL);
@@
constant char *stock_constant =~ "^GTK_STOCK";
@@
-"+" stock_constant
+stock_constant

For starters, Coccinelle doesn't seem to recognize string juxtaposition (spatch gives me an error when
I try this); secondly, I can't seem to get "constant char *p" to match *any* string literals. For example,

int
main(void)
{
const char *p = "bar";
return 0;
}

If I just use "constant p", it'll match the 0 literal in the return statement. I can use "constant int p" to
make only that 0 match, but I'd like to match the "bar" string literal, and "constant char *p" doesn't seem to
work. Is there some way I can get Coccinelle to match only string literals to a metavariable?

Another quick question: is there a way to tell Coccinelle to dump its AST so I can see which type an expression
has been assigned? Having such a tool might help me get more familiar with the tool!

Thanks,
Rob

[Julia Lawall]

Post by Rob Hoelz
Hi Coccinelle community,
I just discovered Coccinelle a few days ago, and already my mind is reeling with the possibilities.
I'm doing some work porting the Claws Mail mail client to GTK3, and I think Coccinelle would be a
great tool to use to accomplish this task.
One of the thing I'm trying to use Coccinelle to do is to detect and patch string concatenation via

...
GTK_STOCK_NO, "+" GTK_STOCK_YES, NULL);
@@
constant char *stock_constant =~ "^GTK_STOCK";
@@
-"+" stock_constant
+stock_constant

For starters, Coccinelle doesn't seem to recognize string juxtaposition (spatch gives me an error when
I try this); secondly, I can't seem to get "constant char *p" to match *any* string literals. For example,

int
main(void)
{
const char *p = "bar";
return 0;
}

If I just use "constant p", it'll match the 0 literal in the return statement. I can use "constant int p" to
make only that 0 match, but I'd like to match the "bar" string literal, and "constant char *p" doesn't seem to
work. Is there some way I can get Coccinelle to match only string literals to a metavariable?

It's constant char[] c. A string is an array.

Post by Rob Hoelz
Another quick question: is there a way to tell Coccinelle to dump its AST so I can see which type an expression
has been assigned? Having such a tool might help me get more familiar with the tool!

No there is nothing like this. There is a BNF in the documentation
(http://coccinelle.lip6.fr/docs/index.html).
People don't find it very user-friendly, but for example here:

http://coccinelle.lip6.fr/docs/main_grammar010.html

you can see that there are possibilities like:

exp metaidAssignOp exp
exp metaidBinOp exp
metaidExp
metaidConst

Unfortunately, none of those names actually correspond to the way in which
one declares those metavariables, which are assignment operator x, binary
operator x, expression, and constant, respectively.

It may be helpful to look at the examples in http://coccinellery.org/

For the concatenated strings, unfortunately the patern matching language
doesn't support that. The only thing you can do is match the full string,
and then do some magic with python to get out the parts you want. I'm not
sure that this is the best first project.

julia

[Rob Hoelz]

On Wed, 10 Jan 2018 09:40:19 +0100 (CET)

Post by Julia Lawall

Post by Rob Hoelz
Hi Coccinelle community,
I just discovered Coccinelle a few days ago, and already my mind is
reeling with the possibilities. I'm doing some work porting the
Claws Mail mail client to GTK3, and I think Coccinelle would be a
great tool to use to accomplish this task.
One of the thing I'm trying to use Coccinelle to do is to detect
and patch string concatenation via string literal juxtaposition;

...
GTK_STOCK_NO, "+" GTK_STOCK_YES, NULL);

I would like to write a spatch that does something like the

@@
constant char *stock_constant =~ "^GTK_STOCK";
@@
-"+" stock_constant
+stock_constant

For starters, Coccinelle doesn't seem to recognize string
juxtaposition (spatch gives me an error when I try this); secondly,
I can't seem to get "constant char *p" to match *any* string

int
main(void)
{
const char *p = "bar";
return 0;
}

If I just use "constant p", it'll match the 0 literal in the return
statement. I can use "constant int p" to make only that 0 match,
but I'd like to match the "bar" string literal, and "constant char
*p" doesn't seem to work. Is there some way I can get Coccinelle
to match only string literals to a metavariable?

It's constant char[] c. A string is an array.

/me facepalms

Of course! What a silly mistake on my part =/ Thanks for clarifying for me!

Post by Julia Lawall

Post by Rob Hoelz
Another quick question: is there a way to tell Coccinelle to dump
its AST so I can see which type an expression has been assigned?
Having such a tool might help me get more familiar with the tool!

No there is nothing like this. There is a BNF in the documentation
(http://coccinelle.lip6.fr/docs/index.html).
http://coccinelle.lip6.fr/docs/main_grammar010.html
exp metaidAssignOp exp
exp metaidBinOp exp
metaidExp
metaidConst
Unfortunately, none of those names actually correspond to the way in
which one declares those metavariables, which are assignment operator
x, binary operator x, expression, and constant, respectively.
It may be helpful to look at the examples in http://coccinellery.org/
For the concatenated strings, unfortunately the patern matching
language doesn't support that. The only thing you can do is match
the full string, and then do some magic with python to get out the
parts you want. I'm not sure that this is the best first project.
julia

Thanks for the quick answer, Julia! I'll try to undertake something a little
simpler to start.

-Rob

[Rob Hoelz]

On Thu, 11 Jan 2018 11:11:10 +0100

I'll try to undertake something a little simpler to start.

Thanks for your understanding of the current software situation.
I hope that you will find another promising source code
transformation task that will work also for you finally. But there
can occasionally occur mismatches for your expectations on an
approach which might look simpler than what can be really performed
with the Coccinelle software at the moment.
Extensions could be developed over time. Are you looking for
additional tools and corresponding support?
Regards,
Markus

I have a number of things I can try with Coccinelle - I think that the string literal
matching one was just one of the more ambitious ones! As far as additional tooling
and support go, I'm just playing around with Coccinelle for the moment.

Thanks,
Rob

[Rob Hoelz]

On Thu, 11 Jan 2018 14:30:16 +0100

@@
constant char *stock_constant =~ "^GTK_STOCK";
@@
-"+" stock_constant
+stock_constant
For starters, Coccinelle doesn't seem to recognize string
juxtaposition (spatch gives me an error when I try this);

It would be nice if this small source code adjustment could be
specified also for the semantic patch language in such a convenient
and succinct way. But the Coccinelle software provides a specific
behaviour for string literals so far. I imagine then that you could
achieve the desired transformation with an other approach.
* How do you think about to choose any of the supported programming
languages for the construction of corresponding SmPL script rules?
http://coccinelle.lip6.fr/docs/main_grammar003.html
* A “constant” could be stored in a script variable by this
metavariable type. http://coccinelle.lip6.fr/docs/main_grammar002.html
The received input string can be adjusted in ways you like by
additional function calls from the available programming interfaces.
Would you like to propagate the constructed value back to another
script rule by calling the SmPL method “make_expr”?
Regards,
Markus

I'm *very* much new to Coccinelle, so I think I'll have to trying the scripting
interface as per Julia's suggestion. I think I need to experiment with Coccinelle
a bit (or a lot!) more to get the hang of it.

-Rob