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# C64 A̶s̶s̶e̶m̶b̶l̶y̶  Machine Code, 2 Bytes

 D0 FE

Branches to itself if the zero flag is not set.

Branches are single-byte offsets from the next instruction location, and 254 is -2 in two's complement... the BNE instruction (D0) takes one byte of memory, and the offset takes a second byte, so branching two bytes back branches back to itself. The zero flag is always cleared when code is loaded into memory. 

Note that this is not a recursive subroutine call, so you will never run out of memory. Also note that there is no header, compiler, or executable overhead... it is truly a two-byte program :)