It's a long time since I tangled with x86 assembler; but as I recall, ENTER and LEAVE were specifically for functions, and I'm not aware of any other use for them.
ENTER and LEAVE were specific x86 instructions though, not some kind of assembler special sauce. The assembler just translated your ENTER instruction into the corresponding machine opcode; no ABI knowledge required whatsoever.
It's a long time since I tangled with x86 assembler; but as I recall, ENTER and LEAVE were specifically for functions, and I'm not aware of any other use for them.