IDA Pro Reverse offset in struct

Question

I'm reversing a Delphi program and have a part where it says:

Result = *(Self - 44);

But I want it to say something like:

Result = *(Self - offsetof(VMT_ClassDefinition, vmtClassName));

Being VMT_ClassDefinition the following struct:

struct VMT_ClassDefinition {
    Cardinal vmtSelfPtr;
    Cardinal vmtIntfTable;
    Cardinal vmtAutoTable;
    Cardinal vmtInitTable;
    Cardinal vmtTypeInfo;
    Cardinal vmtFieldTable;
    Cardinal vmtMethodTable;
    Cardinal vmtDynamicTable;
    Cardinal vmtClassName;
    Cardinal vmtInstanceSize;
    Cardinal vmtParent;
    Cardinal vmtSafeCallException;
    Cardinal vmtAfterConstruction;
    Cardinal vmtBeforeDestruction;
    Cardinal vmtDispatch;
    Cardinal vmtDefaultHandler;
    Cardinal vmtNewInstance;
    Cardinal vmtFreeInstance;
    Cardinal vmtDestroy;
};

Where cardinal is unsigned int. The problem is that after using "Right Click > Struct offset" on top of the number 44 it generates the following result:

Result = *(Self - offsetof(VMT_ClassDefinition, vmtSafeCallException));

I was doing what is said in New features in Hex-Rays Decompiler 1.6 section 3, but as you can see the expected result and what I got is totally different.

My guess is that it forgets about the "-" sign and just advances from the start +44. Is there a way to reverse this behavior? I know it can be done in ASM view by inverting with "_" and then pressing "T" like in Negated structure offsets, but that does not apply to the Pseudocode view.

Answer 1

Shifted pointer should work, I think.

Answer 2

Since there seems to be no other way I ended up converting the Self variable into a pointer to the struct and IDA generated the following code:

Self[-1].vmtClassName

At least it is readable now.