add print subroutine (lol im actually doing stack frame thingy here)

Makefile

@@ -97,7 +97,7 @@ $(OBJ_DIR)/%.o: $(SRC_DIR)/%.s
 	$(AS) $(ASFLAGS) -o $@ $<
 	$(OBJCOPY) --remove-section .note.gnu.property $@
 
-MBR_TEST_OBJ		=	obj/mbr_test.o
+MBR_TEST_OBJ		=	obj/mbr_test.o obj/print.o
 
 mbr_test: $(MBR_TEST_OBJ) $(DISK)
 	$(LD) -T src/mbr_test.ld -o $(BIN_DIR)/mbr_test.bin $(MBR_TEST_OBJ)
@@ -106,6 +106,9 @@ mbr_test_clean:
 	rm $(BIN_DIR)/mbr_test.bin
 	rm $(OBJ_DIR)/mbr_test.o
 
+mbr_test_objdump:
+	objdump -b binary -mi386 -Maddr16,data16 -D $(BIN_DIR)/mbr_test.bin
+
 mbr_test_qemu: mbr_test
 	$(QEMU) -accel tcg,thread=single									\
 			-cpu core2duo												\

src/mbr_test.s

@@ -24,17 +24,15 @@
     # far jump to new memory region
     jmp $0x0050,$.bootloader
 .bootloader:
+    # initialize stack
+    mov $0x07DF, %ax
+    mov %ax, %ss
+    xor %sp, %sp
 
-    mov $msg, %si
+.entry:
-.putc_loop:
+    push $msg
-    lodsb
+    call print
-    or %al, %al
-    jz .halt
 
-    mov $0x0E, %ah
-    mov $0x00, %bh
-    int $0x10
-    jmp .putc_loop
 .halt:
     jmp .halt
 

src/print.s

@@ -0,0 +1,35 @@
+.section .text
+.code16
+
+.globl print
+
+# (%bp)     - old bp
+# 2(%bp)   - ret addr
+# 4(%bp)   - arg 1
+
+# arg 1 - string addr
+print:
+    push %bp
+    mov %sp, %bp
+
+    push %bx
+    push %si
+
+    mov 4(%bp), %si
+    cld
+.putc:
+    lodsb
+    or %al, %al
+    jz .end
+
+    mov $0x0E, %ah
+    xor %bh, %bh
+    int $0x10
+    jmp .putc
+.end:
+
+    pop %si
+    pop %bx
+
+    pop %bp
+    ret