Prekernel: Split early boot printing into two subroutines

Kernel/Prekernel/Arch/x86/boot.S

@@ -98,6 +98,46 @@ code64_sel:
 start:
  jmp real_start
 
+/*
+ param 1: pointer to C string
+ returns: Length of string (including null byte)
+*/
+print_no_halt:
+ pushl %ebp
+ movl %esp, %ebp
+
+ pushl %esi
+ pushl %ecx
+
+ movl 8(%ebp), %esi
+
+ mov $0xb8000, %ecx /* VRAM address. */
+ mov $0x07, %ah /* grey-on-black text. */
+
+.Lprint_str_loop:
+ lodsb /* Loads a byte from address at %esi into %al and increments %esi. */
+
+ test %al, %al
+ jz .Lprint_str_end
+
+ movw %ax, (%ecx)
+ add $2, %ecx
+
+ jmp .Lprint_str_loop
+.Lprint_str_end:
+
+ mov %esi, %eax
+ sub 8(%ebp), %eax
+
+ popl %ecx
+ popl %esi
+
+ movl %ebp, %esp
+ popl %ebp
+ ret
+
+
+
 /* 
  this function assumes that paging is disabled (or everything is mapped 1:1)
  param 1: pointer to string ended with null terminator (C string)
@@ -122,24 +162,13 @@ print_and_halt:
  movl %esp, %ebp
  movl 4(%ebp), %esi
 
- mov $0xb8000, %ecx /* VRAM address. */
- mov $0x07, %ah /* grey-on-black text. */
-
-.print_str_loop:
- lodsb /* Loads a byte from address at %esi into %al and increments %esi. */
-
- test %al, %al
- jz .print_str_end
-
- movw %ax, (%ecx)
- add $2, %ecx
-
- jmp .print_str_loop
-.print_str_end:
+ /* Print string using non-destructive methods */
+ pushl %esi
+ call print_no_halt
+ addl $4, %esp
 
- /* Calculate string length into %ecx */
- mov %esi, %ecx
- sub 4(%ebp), %ecx
+ /* print_no_halt returns the string length (including null byte) in eax. */
+ mov %eax, %ecx
  movw %cx, (COPIED_STRING_LOCATION) /* Store string length for later use. */
 
  /* Copy string into lower memory */