A reason for a function pointer like void (*f)(void) is that C guarantees that all function pointers are 'compatible' in the sense that you can cast a function pointer to a different type of function pointer and then back again and get a working pointer. This is the same guarantee that void* has for object pointers, but void* also adds implicit conversions for which no function pointer type has.
The xDlSym function uses that particular signature, because as you say, it is somewhat unlikely to be used in normal programming (it actually IS a useful type of function, it just needs to interact through global variables). It is expected that you will case the result to the proper type of function pointer before calling the function. On many machines (and I believer required for POSIX) the conversion of a function pointer to a void* and back to the proper type of function pointer would work, giving you a working function pointer. It was never promised by the standard to work in general, and there are machines where it doesn't work (you just need a larger program space than data space). -- Richard Damon
