[Cocci] Matching format strings

[okuznik@symas.com (Ondřej Kuzník)]

On Tue, Jul 04, 2017 at 05:25:46PM +0200, Julia Lawall wrote:
> On Tue, 4 Jul 2017, Ond?ej Kuzn?k wrote:
>> Hmm, suddenly the problems with passing expressions to python I stated
>> earlier disappeared, good. Running this takes a log time on some files
>> (over 10 minutes for ./servers/slapd/back-ldap/bind.c and processing of
>> servers/slapd/back-meta/search.c has yet to finish after 30 minutes of
>> processing).
>>
>> I suppose going through all the potential combinations of snprintf/Debug
>> statements is what takes so long, any tips on what usually helps to
>> speed things up?
> 
> Some functions in those files have a lot of ifs.  Ifs are very expensive,
> because both branches have to be considered.

Do they have to be considered every time or can coccinelle sometimes
understand that taking neither branch can affect the match? (as in, can
I adjust the patch to help coccinelle somehow?).

> In the rule below at least, I don't think you need the initial
> { ... and final ... }.  That would only seem to be necessary if you have a
> lot of redeclarations of variables.

That is the case at least in servers/slapd/back-meta/search.c, where
buf is often declared just before it is used and I hoped that would
speed things up slightly.

> Also, it could help to be more specific about the type of buf.

I have tried

{
-char buf[S];
-snprintf at p1( buf, E, format1, args );
-Debug at p2( L, format2, args_before, buf, args_after );
+Debug( L, merged, args_before, args, args_after );
... when != buf
}

To see whether I can remove a lot of the simple ones quickly and then
work with a simpler file, but this one seems to take the same amount of
time once I put the "... when != buf" in.

>> Also, more importantly, the patch below this seems to remove this
>> comment:
>> https://github.com/openldap/openldap/blob/master/servers/slapd/back-asyncmeta/conn.c#L547
>>
>> [...]
>>
>> I would like to preserve the comment, is there something I can do about
>> that?
> 
> I thought that comments are only removed when they come before removed
> code, while here they come after removed code.  I can check on it.

Thanks!


-- 
Ond?ej Kuzn?k
Senior Software Engineer
Symas Corporation                       http://www.symas.com
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