Re: [DotGNU]Something is broken here, and I don't know what :)

[Gopal V]

Hmmm... a .NET.IL domain ;-)

If memory serves me right, Michael Stolovitzsky wrote:
> Could anyone briefly explain me what are the possible origins of 
> "System.Security.VerificationException: Could not verify the code" and what 
> is the security verification intended to do?

This exception is thrown when the input IL codes fails the bytecode verifier.
a simple example would be a stack underflow (in IL) Other issues like 
typesafety and stack states are checked during verification. I'll explain
more on why pnet uses a verifier (to avoid making this mail looooong)...

As we were talking on IRC , the interface bug is what caused this error 
I'm posting a simplified version of this bug ..

I hope you have got an idea of how to debug such an issue ?....
Uncomment the  /*#define    IL_VERIFY_DEBUG*/ in pnet/engine/verify.c:543
make in the engine dir and try running the ilverify program .

In this case ilverify does not report any bugs ???? ... But ilrun throws
the exception and the VERIFY_ERROR reports the line number and source file
in which it was thrown .. here verify_var.c:294 

SingleLinkedList::.ctor [2076] - stloc.0 at verify_var.c:294
Uncaught exception: System.Security.VerificationException: Could not verify the 
code
    at T..ctor() in test.cs:32
    at MainClass.Main() in test.cs:46

I inspected the verify_var.c code and found that the error was actually in
the AssignCompatible() function in verify.c:426

            /* Is the type a regular class or an interface? */
            if(!ILClass_IsInterface(classInfo))
            {
                /* Regular class: the value must inherit from the type */
                if(ILClassInheritsFrom(classInfo2, classInfo))
                {
                    return 1;
                }

                /* If "classInfo2" is an interface, then the conversion
                   is OK if "type" is "System.Object", because all
                   interfaces inherit from "System.Object", even though
                   the metadata doesn't explicitly say so */
                if(ILClass_IsInterface(classInfo2))
                {
                    return ILTypeIsObjectClass(type);
                }

                /*fprintf(stdout,"<%s> => <0x%08X>\n",ILClass_Name(classInfo),
                                ILClassGetAttrs(classInfo));*/
                /* The conversion is not OK */
                return 0;
            }
    
Eventhough IEnumerator is an interface , ILClass_IsInterface() fails,
further debugging (fprintf) revealed that the Attrs was 0x00000000 instead
of containng 0x00000020 (IL_META_TYPEDEF_INTERFACE)

So there is that bug (and how I debugged it) in detail ... 

Sorry , I couldn't find a way to fix it :-(

Gopal
-- 
The difference between insanity and genius is measured by success

Xenumerator.cs
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