@Override
	public void fixupDWARFFunction(DWARFFunction dfunc) {
		for (DWARFVariable param : dfunc.params) {
			if (!param.isStackStorage()) {
				continue;
			}
			long paramStackOffset = param.getStackOffset();
			if (dfunc.isInLocalVarStorageArea(paramStackOffset) &&
				dfunc.getLocalVarByOffset(paramStackOffset) == null) {

				DWARFVariable paramSpill = DWARFVariable.fromDataType(dfunc, param.type);
				String paramName = param.name.getName();
				paramSpill.name =
					param.name.replaceName(paramName + "_local", paramName + "_local");
				paramSpill.setStackStorage(paramStackOffset);
				dfunc.localVars.add(paramSpill);
				param.clearStorage();
			}
		}
	}
Steal storage location from parameters that are defined in a function's local variable
area, because the storage location isn't the parameter location during call, but its location
after being spilled.

Create a local variable at that storage location.
Ghidra/Features/Base/src/main/java/ghidra/app/util/bin/format/dwarf/funcfixup/ParamSpillDWARFFunctionFixup.java