doughgle · January 26, 2018 10:32
diff --git a/myfunc.s b/myfunc.s
 	.file	"example.c"						# filename
 	.text												# store in text section
 	.globl	myfunc							# exported symbol
 	.type	myfunc, @function			#
 myfunc:												# function name
 .LFB0:
 	.cfi_startproc							#### PROLOGUE
 	pushq	%rbp									# push base pointer (64bit) onto the stack
 	.cfi_def_cfa_offset 16
 	.cfi_offset 6, -16
 	movq	%rsp, %rbp						# start a new stack frame, 
                              # move the value of stack pointer to base pointer
 	.cfi_def_cfa_register 6
 															#### PROLOGUE END

 	movl	%edi, -20(%rbp)				# move 32bit reg value onto stack
 	movq	$0, -16(%rbp)					# move the 64bit value 0 into the address pointed to by rbp -16
 	movl	$0, -4(%rbp)					# zero a few bytes...?
 	jmp	.L2											# jump to label
 .L5:
 	movl	-4(%rbp), %eax				# put 0 in eax
 	imull	-20(%rbp), %eax				# multiply src x dest ; i.e. value * 0
 	cltq												# sign-extend the value in eax to fill rax
 	addq	%rax, -16(%rbp)				# rax + 0
 	movl	-4(%rbp), %eax				# reset eax
 	andl	$1, %eax							# bitwise AND 0b1 & eax
 	testl	%eax, %eax
 	je	.L3											# goto L3
 	movq	globl_cnt(%rip), %rax	# rdx = (&rip + globl_cnt)
 	subq	-16(%rbp), %rax				# result = rax - (&rbp - 16)
 	movq	%rax, globl_cnt(%rip) # store result
 	jmp	.L4
 .L3:													# globl_cnt is a global counter of the type “long int” external to the function.
 	movq	globl_cnt(%rip), %rdx # offset globl_cnt bytes from intruction pointer and move value to rdx
 	movq	-16(%rbp), %rax				# move basepointer -16 bytes to rax
 	addq	%rdx, %rax						# rdx + rax
 	movq	%rax, globl_cnt(%rip) # move result to offset instruction pointer
 .L4:
 	addl	$1, -4(%rbp)					# (rbp add -4 bytes) + 1 ;  i.e. increment some variable
 .L2:													#
 	movl	-4(%rbp), %eax				# move the value 4 bytes below the base pointer to eax register
 	cmpl	-20(%rbp), %eax				# compare the value 0x20 bytes below the base pointer with the value in eax register (0?)
 	jl	.L5											# jump to L5 if value < 0
 	nop
 	popq	%rbp									# pop the parent stack frame address
 	.cfi_def_cfa 7, 8
 	ret													# pop return address and jump there
 	.cfi_endproc
 .LFE0:
 	.size	myfunc, .-myfunc
 	.ident	"GCC: (GNU) 6.1.0"
 	.section	.note.GNU-stack,"",@progbits
	.file "example.c" # filename
	.text # store in text section
	.globl myfunc # exported symbol
	.type myfunc, @function #
	myfunc: # function name
	.LFB0:
	.cfi_startproc #### PROLOGUE
	pushq %rbp # push base pointer (64bit) onto the stack
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq %rsp, %rbp # start a new stack frame,
	# move the value of stack pointer to base pointer
	.cfi_def_cfa_register 6
	#### PROLOGUE END

	movl %edi, -20(%rbp) # move 32bit reg value onto stack
	movq $0, -16(%rbp) # move the 64bit value 0 into the address pointed to by rbp -16
	movl $0, -4(%rbp) # zero a few bytes...?
	jmp .L2 # jump to label
	.L5:
	movl -4(%rbp), %eax # put 0 in eax
	imull -20(%rbp), %eax # multiply src x dest ; i.e. value * 0
	cltq # sign-extend the value in eax to fill rax
	addq %rax, -16(%rbp) # rax + 0
	movl -4(%rbp), %eax # reset eax
	andl $1, %eax # bitwise AND 0b1 & eax
	testl %eax, %eax
	je .L3 # goto L3
	movq globl_cnt(%rip), %rax # rdx = (&rip + globl_cnt)
	subq -16(%rbp), %rax # result = rax - (&rbp - 16)
	movq %rax, globl_cnt(%rip) # store result
	jmp .L4
	.L3: # globl_cnt is a global counter of the type “long int” external to the function.
	movq globl_cnt(%rip), %rdx # offset globl_cnt bytes from intruction pointer and move value to rdx
	movq -16(%rbp), %rax # move basepointer -16 bytes to rax
	addq %rdx, %rax # rdx + rax
	movq %rax, globl_cnt(%rip) # move result to offset instruction pointer
	.L4:
	addl $1, -4(%rbp) # (rbp add -4 bytes) + 1 ; i.e. increment some variable
	.L2: #
	movl -4(%rbp), %eax # move the value 4 bytes below the base pointer to eax register
	cmpl -20(%rbp), %eax # compare the value 0x20 bytes below the base pointer with the value in eax register (0?)
	jl .L5 # jump to L5 if value < 0
	nop
	popq %rbp # pop the parent stack frame address
	.cfi_def_cfa 7, 8
	ret # pop return address and jump there
	.cfi_endproc
	.LFE0:
	.size myfunc, .-myfunc
	.ident "GCC: (GNU) 6.1.0"
	.section .note.GNU-stack,"",@progbits