a página man do objdump diz para usar --insn-width:
$ objdump -d a.out | grep movabs
40053e: 48 b8 45 23 12 90 78 movabs $0x1234567890122345,%rax
40054c: 48 b8 45 33 12 90 73 movabs $0x1334567390123345,%rax
$ objdump --insn-width=10 -d a.out | grep movabs
40053e: 48 b8 45 23 12 90 78 56 34 12 movabs $0x1234567890122345,%rax
40054c: 48 b8 45 33 12 90 73 56 34 13 movabs $0x1334567390123345,%rax