print ascii reverse

Author: Leonhard Bromoloron

README.md

@@ -2,6 +2,10 @@
 
 [Linux System Call Table](https://blog.rchapman.org/posts/Linux_System_Call_Table_for_x86_64)
 
+[x86 registers](https://wiki.osdev.org/CPU_Registers_x86)
+
+[x86 assembly language](https://en.wikipedia.org/wiki/X86_assembly_language)
+
 ```
 /usr/include/asm-generic/fcntl.h
 ```

draft/Makefile

@@ -1,6 +1,7 @@
 CFLAGS += -D_GNU_SOURCE
 CFLAGS += -Wall
 CFLAGS += -pedantic-errors
+CFLAGS += -Og
 
 draft: draft.c
 	$(CC) $(CFLAGS) -fno-omit-frame-pointer -g -o draft $^

draft/count_memi.s

@@ -0,0 +1,62 @@
+	.file	"draft.c"
+	.text
+	.globl	main
+	.type	main, @function
+main:
+.LFB23:
+	.cfi_startproc
+	pushq	%rbp
+	.cfi_def_cfa_offset 16
+	.cfi_offset 6, -16
+	movq	%rsp, %rbp
+	.cfi_def_cfa_register 6
+	subq	$16, %rsp
+	movl	i(%rip), %eax
+	leal	1(%rax), %ecx
+	movl	%ecx, i(%rip)
+	movslq	%eax, %rdx
+	movb	$48, -5(%rbp,%rdx)
+	leal	2(%rax), %edx
+	movl	%edx, i(%rip)
+	movslq	%ecx, %rcx
+	movb	$120, -5(%rbp,%rcx)
+	leal	3(%rax), %ecx
+	movl	%ecx, i(%rip)
+	movslq	%edx, %rdx
+	movb	$52, -5(%rbp,%rdx)
+	leal	4(%rax), %edx
+	movl	%edx, i(%rip)
+	movslq	%ecx, %rcx
+	movb	$49, -5(%rbp,%rcx)
+	addl	$5, %eax
+	movl	%eax, i(%rip)
+	movslq	%edx, %rdx
+	movb	$10, -5(%rbp,%rdx)
+	leaq	-5(%rbp), %rdx
+	movl	$5, %ecx
+	movl	$1, %esi
+	movl	$1, %edi
+	movl	$0, %eax
+	call	syscall@PLT
+	movl	$0, %eax
+	leave
+	.cfi_def_cfa 7, 8
+	ret
+	.cfi_endproc
+.LFE23:
+	.size	main, .-main
+	.globl	i
+	.bss
+	.align 4
+	.type	i, @object
+	.size	i, 4
+i:
+	.zero	4
+	.globl	fh
+	.align 4
+	.type	fh, @object
+	.size	fh, 4
+fh:
+	.zero	4
+	.ident	"GCC: (Debian 14.2.0-19) 14.2.0"
+	.section	.note.GNU-stack,"",@progbits

print_int/.gdbinit

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

print_int/.gitignore

@@ -1 +1 @@
-hello
+/print_int

print_int/print_int

@@ -22,7 +22,7 @@
 	.text
 	.globl _start
 
-# void print_chars(char *rsi, int rdx);
+# char *rsi, int rdx;
 print_chars:
 	movq	$WRITE, %rax
 	movq	$STDOUT, %rdi
@@ -35,8 +35,11 @@ print_int:
 	push	%rbp
 	push	%rsi
 	push	%rdx
+	push	%rcx
 	mov	%rsp, %rbp 	# save stack pointer
-	push	$0xa		# "\n"
+	mov	$0, %rcx
+	movb	$0xa, -64(%rbp, %rcx)
+	inc	%rcx
 print_int_loop:
 	mov	%rsi, %rax
 	and	$15, %rax
@@ -45,17 +48,21 @@ print_int_loop:
 	jle	print_int_after_adjust
 	add	$39, %rax	# adjust for ascii "a"-"f"
 print_int_after_adjust:
-	push	%rax
+	movb	%al, -64(%rbp, %rcx)
+	inc	%rcx
 	shr	$4, %rsi
 	test	%rsi, %rsi
 	jnz	print_int_loop
-	push	$0x78		# "x"
-	push	$0x30		# "0"
-	mov	%rsp, %rsi
-	mov	%rbp, %rdx
-	sub	%rsp, %rdx	# print from rsp to rbp
+	movb	$0x78, -64(%rbp, %rcx)
+	inc	%rcx
+	movb	$0x30, -64(%rbp, %rcx)
+	inc	%rcx
+	leaq	-64(%rbp), %rsi
+	mov	%rcx, %rdx	# len
+le_print:
 	call	print_chars
 	mov	%rbp, %rsp 	# restore stack pointer
+	pop	%rcx
 	pop	%rdx
 	pop	%rsi
 	pop	%rbp