hello deadbeef

Author: h908714124

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

draft/draft.c

@@ -6,17 +6,20 @@
 #include <sys/syscall.h>
 #include <sys/types.h>
 
-int fh = 0;
-int i = 0;
-
 int main(int argc, char *argv[])
 {
-	char out[5];
-	out[i++] = '0';
-	out[i++] = 'x';
-	out[i++] = '4';
-	out[i++] = '1';
-	out[i++] = '\n';
-	syscall(__NR_write, 1, out, 5);
+	char out[11];
+	out[0] = '0';
+	out[1] = 'x';
+	out[2] = 'd';
+	out[3] = 'e';
+	out[4] = 'a';
+	out[5] = 'd';
+	out[6] = 'b';
+	out[7] = 'e';
+	out[8] = 'e';
+	out[9] = 'f';
+	out[10] = '\n';
+	syscall(__NR_write, 1, out, 11);
 	return 0;
 }

hello/Makefile

@@ -2,5 +2,8 @@ default:
 	$(CC) hello.s -c -g
 	$(LD) -o hello hello.o
 
+check:
+	./hello | md5sum | grep -q ^823c843e5 && printf "\033[1;32m[OK]\033[0m\n"
+
 run:
 	./hello

hello/hello.s

@@ -1,27 +1,27 @@
-#https://www.youtube.com/watch?v=3nYHV5zIQGA
-.globl _start
-
-.hello.str:
-	.asciz "12345678\n"
-
-.text
-
-# void print_chars(int {rsi}, int {rdx});
-print_chars:
-	movq	$1, %rax
-	movq	$1, %rdi
-	syscall
-	ret
-
+	.text
+	.globl	_start
 _start:
-	#https://stackoverflow.com/questions/29790175/assembly-x86-leave-instruction
 	pushq	%rbp
 	movq	%rsp, %rbp
+	movb	$48, -11(%rbp)
+	movb	$120, -10(%rbp)
+	movb	$100, -9(%rbp)
+	movb	$101, -8(%rbp)
+	movb	$97, -7(%rbp)
+	movb	$100, -6(%rbp)
+	movb	$98, -5(%rbp)
+	movb	$101, -4(%rbp)
+	movb	$101, -3(%rbp)
+	movb	$102, -2(%rbp)
+	movb	$10, -1(%rbp)
+	mov	$11, %rdx
+	leaq	-11(%rbp), %rsi
+	mov	$1, %rdi
+	mov	$1, %rax
+	syscall
+	jmp	exit
 
-	leaq	.hello.str, %rsi
-	movq	$10, %rdx
-	call	print_chars
-
+exit:
 	movq	$60, %rax
 	movq	$0, %rdi
 	syscall

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