The smallest you can make an ELF binary under Linux is 45 bytes. You only have eight bytes for code, but it can be done. Fortunately Rob's version can be squeezed into that. So here it is (ported from nasm to gas):
.data .code32 ehdr: .byte 0x7F, 'E', 'L', 'F' .int 1 .int 0 .int 0x1000 .hword 2 .hword 3 .int filesize .int _start + 0x1000 .int 4 _start: movb $36, %al int $0x80 movb $1, %al int $0x80 .hword 0x34 .hword 0x20 .byte 1 filesize = .
as sync.s -o sync.o ld -pie -s --oformat binary sync.o -o sync
When I run it my disk drive light illuminates. That is all I can accurately say about this code.