'PointerType' object has no attribute 'type' - llvm

Question

I'm trying convert this raw LLVM code:
%UnwEx = type { i64, i8*, i64, i64 }
#UnwEx.size = constant i64 ptrtoint (%UnwEx* getelementptr (%UnwEx* null, i32 1) to i64)
To the llvmlite:
unw_ex = context.get_identified_type("UnwEx")
unw_ex.elements = [int_, i8_ptr, int_, int_]
i32 = ir.IntType(32)
gep = builder.gep(ir.PointerType(unw_ex), [i32(1)], name="gep")
... # some extra code to cast gep to integer
The idea is get the size of the structured type UnwEx in runtime. However the last line with get command raise this:
Traceback (most recent call last):
File "C:/Users/DavidRagazzi/Desktop/mamba/mamba/core/runtime.py", line 495, in <module>
generate(None, 64, 8)
File "C:/Users/DavidRagazzi/Desktop/mamba/mamba/core/runtime.py", line 280, in generate
gep = builder.gep(unw_ex_ptr, [i32(1)], name="gep")
File "C:\Program Files\Python37\lib\site-packages\llvmlite\ir\builder.py", line 925, in gep
inbounds=inbounds, name=name)
File "C:\Program Files\Python37\lib\site-packages\llvmlite\ir\instructions.py", line 494, in __init__
typ = ptr.type
AttributeError: 'PointerType' object has no attribute 'type'
What's wrong with this? Is there a better way to get the size of type?

Answer 1

The first argument to gep should be a value that is pointer to an instance UnwEx. What you're passing is a type, not a value. The way you get that pointer is by allocating memory using alloca or malloc (in which case you'd have to bitcast the returned pointer to UnwEx*).
Another way of getting UnwEx's size is by using its get_abi_size member. Something like
target = llvmlite.binding.Target.from_default_triple()
target_machine = target.create_target_machine()
unw_ex_size = unw_ex.get_abi_size(target_machine.target_data)
gives you the size of in bytes an instance of UnwEx would occupy on your host platform.