When using C, this can return anything (or crash of oracle function returns an invalid pointer, or rewrite its own code if the code section is writable). So if you get rid of "abstract machine", nothing changes - the program can return anything or crash.
The point is that the C standard does guarantee that the function returns 1 if the program is a valid C program - which means there is no UB.
For example: If the oracle function returns an invalid pointer, then dereferencing that pointer is UB, and therefore the program isn't a valid C program.
