SYSCALL - x86-64 instruction reference

syscallFast system call to the operating system 
Asks the operating system to do something.
x86-64 and later
Intel's reference: SYSCALL 
Used in Getting started with x86-64x86-64 assembly
The 16 registers and their halvesx86-64 assembly
Memory, little endian and sizesx86-64 assembly
Bytes, words, dwords and qwordsx86-64 assembly
The x86-64 instruction setx86-64 assembly
Effective addressesx86-64 assembly
The flags registerx86-64 assembly
Sections, directives and labelsx86-64 assembly
Memory regions and executable filesx86-64 assembly
cmp and the conditional jumpsx86-64 assembly
 
CFPFAFZFSFDFOF –––––––
Changes no flag
The processor masks the flags on its way into the kernel and Linux restores them on the way out, so after the call they are as the program left them; `r11` holds the copy saved on entry.
Forms  syscall  
rax holds the call number, the arguments go in rdi, rsi, rdx, r10, r8 and r9 in that order, and the result comes back in rax, with a small negative number meaning an error. rcx and r11 are destroyed by the call itself, so anything kept in them has to be saved first.
Programs here run as Linux programs, so this is the only way a program reaches the console or the file system. The syscall page lists the calls this emulator implements.
 global _start

section .data
message: db "hello, world", 10, 0

section .text
_start:
        mov rax, 1          ; syscall 1: write
        mov rdi, 1          ; to standard output
        mov rsi, message    ; from this address
        mov rdx, 14         ; this many bytes
        syscall

        mov rax, 60         ; syscall 60: exit
        xor rdi, rdi
        syscall