Is it possible to define an array of variable size in Ghidra (size in the struct itself)

Question

I have a struct that holds an array (and other elements), and one of the elements is actually the size of the array. Is there a way to define a struct like that in Ghidra?

16          | Size of array is 0x16 
00 
00 
04
00 00 00 00
10 08 0a 04
...
dc c1 50 08 |
74 cf 50 08 | Array of size 0x16
14 dd 50 08 |
(.........) |

Answer 1

Ghidra flexible arrays support what you are trying to do. From Ghidra help (search for "flexible array"):

A flexible array is added to the end of a structure by adding a last row specified by the base DataType (e.g. char) then invoking the array action and specifying an element count of 0.

So you can't create a flexible array in 1 step. Enter the data type for the variable-length structure member first. Then select the row for that new structure member and press the [ key to invoke the array action. Entering 0 as the element count in the resulting dialog will create a flexible array.

Ghidra flexible arrays have limited functionality. From Ghidra help:

The use of flexible array components is not currently reflected in decompiler results or listing reference markup. Its primary purpose if to reflect the C/C++ source definition of a structure with correct alignment and structure sizing.

While C/C++ support flexible arrays anywhere within a structure, Ghidra only supports the case where it is the last structure component.