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Editorial Team
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Asked: 2026-06-04T07:15:44+00:00

I’ve modified the bytecode of an assembly to get rid off of an error

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I’ve modified the bytecode of an assembly to get rid off of an error and now when I try to use it I get a InvalidProgramException.
All I’ve done is replace this code with NOPS:

catch (Exception exception1)
{
    Exception exception = exception1;
    if (exception as InvalidValueException == null)
    {
        throw new InvalidGenerationException(2);
    }
    else
    {
        throw exception;
    }
}

IL before:

catch [mscorlib]System.Exception
{
    IL_022f: stloc.s exception
    IL_0231: ldloc.s exception
    IL_0233: isinst Custom.InvalidValueException
    IL_0238: brfalse.s IL_023d

    IL_023a: ldloc.s exception
    IL_023c: throw

    IL_023d: ldc.i4.1
    IL_023e: newobj instance void Custom.InvalidGenerationException ...
    IL_0243: throw
}

IL after:

catch [mscorlib]System.Exception
{
    IL_022f: nop
    IL_0230: nop
    IL_0231: nop
    IL_0232: nop
    IL_0233: nop
    IL_0234: nop
    IL_0235: nop
    IL_0236: nop
    IL_0237: nop
    IL_0238: nop
    IL_0239: nop
    IL_023a: nop
    IL_023b: nop
    IL_023c: nop
    IL_023d: nop
    IL_023e: nop
    IL_023f: nop
    IL_0240: nop
    IL_0241: nop
    IL_0242: nop
    IL_0243: nop
}

Any ideas about why is this wrong?

Thanks!

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1 Answer

  1. Editorial Team

    Your original catch block will always throw. That is, there’s no way to exit the block “normally”.

    Your modified catch block doesn’t throw so you need to exit the block normally. You’ll need to use leave or leave.s to do that.

    (You might also need to pop the caught exception off the stack to keep things tidy. I’m not sure about that one though, you’ll have to try it and see for yourself.)

    catch [mscorlib]System.Exception
{
    IL_022f: pop                // not certain if pop is necessary
    IL_0230: leave.s IL_0244
    IL_0232: nop
    IL_0233: nop
    IL_0234: nop
    IL_0235: nop
    IL_0236: nop
    IL_0237: nop
    IL_0238: nop
    IL_0239: nop
    IL_023a: nop
    IL_023b: nop
    IL_023c: nop
    IL_023d: nop
    IL_023e: nop
    IL_023f: nop
    IL_0240: nop
    IL_0241: nop
    IL_0242: nop
    IL_0243: nop
}
IL_0244: ret    // or whatever
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