add print_char and a todo

Author: h908714124

README.md

@@ -6,6 +6,8 @@
 
 [x86 assembly language](https://en.wikipedia.org/wiki/X86_assembly_language)
 
+[What is stack frame](https://stackoverflow.com/questions/3699283/what-is-stack-frame-in-assembly)
+
 ```
 /usr/include/asm-generic/fcntl.h
 ```

print_int/.gdbinit

@@ -3,4 +3,4 @@ lay asm
 define hook-quit
 	set confirm off
 end
-break le_print
+break print_int_pop_loop

print_int/Makefile

@@ -6,7 +6,7 @@ run: build
 	./print_int
 
 check: build
-	./print_int | md5sum | grep -q ^823c843e5 && printf "\033[1;32m[OK]\033[0m\n"
+	./print_int | md5sum | grep -q ^0d0f199 && printf "\033[1;32m[OK]\033[0m\n"
 
 clean:
 	rm -f print_int

print_int/print_int.s

@@ -9,6 +9,30 @@
 	.text
 	.globl main
 
+# char rdi
+print_char:
+	push	%rbp
+	mov	%rsp, %rbp
+	push	%rax
+	push	%rcx
+	push	%rdx
+	push	%rsi
+	push	%rdi
+	mov	$WRITE, %rax
+	mov	%rdi, -128(%rbp)
+	lea	-128(%rbp), %rsi
+	mov	$STDOUT, %rdi
+	mov	$1, %rdx
+	syscall
+	pop	%rdi
+	pop	%rsi
+	pop	%rdx
+	pop	%rcx
+	pop	%rax
+	mov	%rbp, %rsp
+	pop	%rbp
+	ret
+
 # char *rsi, int rdx
 write_string:
 	mov	$WRITE, %rax
@@ -23,37 +47,54 @@ print_int:
 	push	%rsi
 	push	%rdx
 	push	%rcx
+	push	%rdi
 	mov	%rsp, %rbp 	# save stack pointer
+
 	mov	$0, %rcx
+
 print_int_push_loop:
 	mov	%rsi, %rax
-	and	$15, %rax
-	add	$48, %rax	# %rax now contains ascii "0"-"9"
-	cmp	$57, %rax
+	and	$0xf, %rax
+	add	$0x30, %rax	# %rax now contains ascii "0"-"9"
+	cmp	$0x39, %rax
 	jle	print_int_after_adjust
 	add	$39, %rax	# adjust for ascii "a"-"f"
 print_int_after_adjust:
+	#movb	%al, -64(%rbp, %rcx)	#to do: use this instead of push
 	push	%rax
 	inc	%rcx
 	shr	$4, %rsi
 	test	%rsi, %rsi
 	jnz	print_int_push_loop
+
+	add	$2, %rcx
+
 	mov	$0, %rdx
+
 	movb	$0x30, -128(%rbp, %rdx)
 	inc	%rdx
+
 	movb	$0x78, -128(%rbp, %rdx)
 	inc	%rdx
+
 print_int_pop_loop:		# copy chars from stack
 	pop	%rax
+
+	mov	%rax, %rdi
+	#call	print_char
+
 	movb	%al, -128(%rbp, %rdx)
 	inc	%rdx
-	cmp	%rsp, %rbp
+	cmp	%rdx, %rcx
 	jne	print_int_pop_loop
+
 	movb	$0xa, -128(%rbp, %rdx)
 	inc	%rdx
+
 	lea	-128(%rbp), %rsi
 	call	write_string
 	mov	%rbp, %rsp 	# restore stack pointer
+	pop	%rdi
 	pop	%rcx
 	pop	%rdx
 	pop	%rsi
@@ -62,9 +103,9 @@ print_int_pop_loop:		# copy chars from stack
 	ret
 
 main:
-	mov	$0xdead, %rsi
+	mov	$0x9084, %rsi
 	shl	$16, %rsi
-	add	$0xbeef, %rsi
+	add	$0xa412, %rsi
 	call	print_int
 	jmp	exit