Printing an integer to stdout with printf in 64-bit NASM (Linux)

64bitprintfintTut

Printing an integer to stdout with printf in 64-bit NASM (Linux)

While doing some debugging, I found myself wanting to print an address to the screen, and it
took me forever to piece together how to do it from several tutorials.
The main things you need to know are
1) use 'main:' as a label and not '_start:' - because you are calling libc, it won't work without main.
2) compile or link with -lc (that's short for libc). 
3) declare printf as extern
4) zero the vector registers (put 0 into rax). I don't know why, but apparently you are supposed to.

The following program is compiled thusly:
nasm -f elf64 -o test.o test.s
gcc -o test test.o -lc

and prints:
404000
to stdout

;;;; Print a number to stdout

extern printf

global main

section .text
main:
    mov rdi,printf_format
    mov rsi,0x404000
    xor rax,rax
    call printf


    mov rax,60	; exit
    syscall


section .data
    printf_format: db '%x',10,0

https://stackoverflow.com/questions/36007975/compile-error-relocation-r-x86-64-pc32-against-undefined-symbol/41322328#41322328
It seems for some people -- at least, for me -- this is necessary.
So for anyone looking at this, if

call printf

doesn't work, try

call printf WRT ..plt