On a bigger CPU maybe. To plop code anywhere in memory to need to only use relative instructions. The 8052 does not give you a full set.
The stack if you are using a compiler that does not use the stack more issues it uses a chunk of code for local.
there is compiler library calls. Two sets of set up code.

Now a call to an asm function all you need is an address.
A function from the same compiler? Well that is a compiler specific. If you can get it to setup a single uncalled function an locate it You are set. Many support this for bootloader use.