[Soot-list] duplicate subgraphs in CFG

[hsadat at gmail.com]

Thanks Eric.

You're right. Actually, I was partly confused because I had no "throw"- 
ending path in the CFG; but after I scrolled to the right, it was  
right there! (I'm using brief CFG, so, I get a forest.)

Now, what you said explains the duplication for "normal" and  
"exceptional" paths; however, the subgraph is also duplicated for two  
different paths that both merge into normal return. Here is my example  
(see the attached png for the CFG):

try{
	f();
}
catch(IOException)
{
	g();
}
finally{
	h();
}

Please see the attached CFG.

So, the flow from catch (handled exception) and try (normal flow) both  
merge into finally block. Therefore, there's no need for duplicate h()  
nodes for these two paths. Am I missing another thing? (Sorry if I'm  
asking dumb questions ...)

--Hossein
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On 4-Dec-08, at 5:43 PM, Eric Bodden wrote:

> The duplication is simply to implement the correct semantics. If you  
> have...
>
> try{
>  foo();
> } finally {
>  bar();
> }
>
> ... then you need something like ...
>
> label1:
>  foo();
> label2:
>  bar();
>  return;
> label3:
>  e = @caughtexception;
>  bar();
>  throw e;
>
> trap Throwable from label1 to label2 with label3;
>
> ... on the Jimple level because you want to execute bar() *regardless*
> of the exception being thrown, but you obviously want to return *or*
> throw depending on whether an exception was raised within the try
> block. The label/location of the copied block therefore sort of
> encodes the information "exception" or "no exception".
>
> Eric
>
>
>
> 2008/12/4  <hsadat at gmail.com>:
>> Hi,
>>
>> I was looking at the CFGs built in interactive mode using Soot  
>> Eclipse
>> plugin and noticed that there are some duplicate subgraphs;  
>> specifically,
>> the subgraph corresponding to "finally" block is repeated, one for  
>> the path
>> from the end of the catch block and the other for the path from end  
>> of try
>> block. Has anyone encountered this? and is there an explanation  
>> behind it?
>>
>> I tried to think of possible reasons for duplicating; because I  
>> know in the
>> analysis context, some of the nodes are created to make later
>> analysis/transformation easier (e.g. "nop" nodes).
>>
>> So, any clues?
>>
>> Thanks
>>
>> --Hossein
>> _______________________________________________
>> Soot-list mailing list
>> Soot-list at sable.mcgill.ca
>> http://mailman.cs.mcgill.ca/mailman/listinfo/soot-list
>>
>
>
>
> -- 
> Eric Bodden
> Sable Research Group, McGill University, Montr?al, Canada
> Got an interesting job offer? http://www.bodden.de/hire-me/