define bootloader size in linker script so later I can use it for relocating bootloader to 0050:0000 memory region

Makefile

@@ -5,6 +5,7 @@ OBJCOPY				=	objcopy
 CLFAGS				=	-g -Wall
 ASFLAGS				=
 LDFLAGS				=	-g
+QEMU				=	qemu-system-x86_64
 
 SRC_DIR				=	src
 OBJ_DIR				=	obj
@@ -105,6 +106,20 @@ mbr_test_clean:
 	rm $(BIN_DIR)/mbr_test.bin
 	rm $(OBJ_DIR)/mbr_test.o
 
+mbr_test_qemu: mbr_test
+	$(QEMU) -accel tcg,thread=single									\
+			-cpu core2duo												\
+			-m 128														\
+			-no-reboot													\
+			-serial stdio												\
+			-smp 1														\
+			-vga std													\
+			-d int														\
+			-d guest_errors												\
+			-s															\
+			-drive format=raw,media=disk,file=$(BIN_DIR)/mbr_test.bin	\
+			-drive format=raw,media=disk,file=$(BIN_DIR)/disk.img
+
 clean:
 	rm -f bin/*
 	rm -f obj/*

src/mbr_test.ld

@@ -1,18 +1,21 @@
 MEMORY
 {
-    BOOTLOADER  (RWX)   :   ORIGIN = 0x7C00, LENGTH = 440
-    UNIQUE_ID   (R)     :   ORIGIN = 0x7DB8, LENGTH = 4
-    RESERVED    (R)     :   ORIGIN = 0x7DBC, LENGTH = 2
-    PTABLE      (R)     :   ORIGIN = 0x7DBE, LENGTH = 64
-    MBR_MAGIC   (R)     :   ORIGIN = 0x7DFE, LENGTH = 2
+    BOOTLOADER  (RWX)   :   ORIGIN = 0x0000, LENGTH = 440
+    UNIQUE_ID   (R)     :   ORIGIN = 0x01B8, LENGTH = 4
+    RESERVED    (R)     :   ORIGIN = 0x01BC, LENGTH = 2
+    PTABLE      (R)     :   ORIGIN = 0x01BE, LENGTH = 64
+    MBR_MAGIC   (R)     :   ORIGIN = 0x01FE, LENGTH = 2
 }
 
 SECTIONS
 {
-    . = 0x7C00;
+    . = 0;
     .text : {
+        BOOTLOADER_START = .;
         *(.text)
         *(.data)
+        BOOTLOADER_END = .;
+        BOOTLOADER_SIZE = BOOTLOADER_END - BOOTLOADER_START;
     } > BOOTLOADER
 
     .unique_id : {

src/mbr_test.s

@@ -1,21 +1,24 @@
 .section .text
 .code16
 
+    mov $BOOTLOADER_SIZE, %ax
+
     mov $0x07C0, %ax
-    mov %ax, %dx
+    mov %ax, %ds
 
     mov msg, %si
+    cld
 .putc_loop:
     lodsb
     or %al, %al
     jz .halt
 
     mov $0x0E, %ah
-    mov $0, %al
+    mov $0x00, %bh
     int $0x10
     jmp .putc_loop
 .halt:
-    hlt
+    jmp .halt
 
 .section .data
-msg:    .asciz "Test MBR hello world\x0D\x0A" # len 22
+msg:    .asciz "Test MBR hello world\r\n"