Re: [xmlvm-users] Try catch crashes

[Arno P. <ar...@pu...>]

that is a known bug. Flow control in the JVM is represented by absolute 
jumps which we simply map to gotos in Objective-C. Exceptions sometimes 
cause the problems you are experiencing. We have discussed for a long 
time to convert the stack machine to register machine that would also 
reverse engineer flow control by removing the gotos. This is no easy 
matter and is further down on our to-do list. In the meantime you can 
probably get around the problem by inserting a dummy statement just 
before the try. Something like:

   } else {
        int x = 42;
        try {

Arno


Markus Heberling wrote:
> Hi,
> 
> I have the following java code:
> 
>         if(args==null){
>                    System.out.println(1);
>         }else{
>             try{
>                 System.out.println(2);
> 
>             }   catch(Exception e){
>                 System.out.println(3);
> 
>             }
>         }
> 
> It gets converted to the following ObjectiveC code (only relevant part here)
> 
>     if (_op1.o != [NSNull null]) goto label0;
>     _op1.o = [java_lang_System _GET_out];
>     _stack[_sp++].o = _op1.o;
>     _stack[_sp++].i = 1;
>     _sp -= 2;
>     [((java_io_PrintStream*) _stack[_sp].o) println___int:_stack[_sp + 1].i];
>     goto label1;
>     @try {
>     label0:;
>     _op1.o = [java_lang_System _GET_out];
>     _stack[_sp++].o = _op1.o;
>     _stack[_sp++].i = 2;
>     _sp -= 2;
>     [((java_io_PrintStream*) _stack[_sp].o) println___int:_stack[_sp + 1].i];
>     } @catch (java_lang_Exception* _ex) {
>         _stack[_sp++].o = _ex;
>         goto label7;
>     }
> 
> This code crashes. The label0 is inside the try and the code jumps into it from the outside. This seems not to be allowed in ObjectiveC. if I move the label0:; before the try manually, it works. The xsl would need to be changed, so that if there is a jvm:label directly after a jvm:catch, they have to be swapped. I tried but wasn't able to do this myself. Don't know if it has any side effects, too :/
> 
> Markus
> 
> 
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