helloworld.s

	.section	__TEXT,__text,regular,pure_instructions
	.macosx_version_min 10, 12
	.globl	_main
	.p2align	4, 0x90
_main:                                  ## @main
	.cfi_startproc
## BB#0:
	pushq	%rbp
Ltmp0:
	.cfi_def_cfa_offset 16
Ltmp1:
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
Ltmp2:
	.cfi_def_cfa_register %rbp
	leaq	L_.str(%rip), %rdi
	xorl	%eax, %eax
	callq	_printf
	xorl	%eax, %eax
	popq	%rbp
	retq
	.cfi_endproc

	.section	__TEXT,__cstring,cstring_literals
L_.str:                                 ## @.str
	.asciz	"Hello World!\n"


.subsections_via_symbols

What does all this mean? What's the leaq call on line 16 doing to %rip? What are all the directives?!

Hi I'll take a crack at trying to explain this...

Lines 8, 13: Prepare a new stack frame (save the old base pointer, and set
the new base pointer to the current stack pointer)

Lines 16: Get the address of your string (lea = load effective address)
and put it into the rdi register as a parameter to printf. %rip is the instruction
pointer, and the code uses that to find the string literal below.

Line 17: Not sure why this is needed - I believe it sets eax to zero. Must be another parameter to printf

Line 18: Call printf

Line 19: Same thing here - set eax to zero, which is now the return value of the function

Lines 20,21: Restore the old stack frame and return to the caller

Line 26: The string literal referenced by leaq.