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#define WHITE_TEXT 0x07	/* White text on a black screen */
#define VIDMEMPTR 0xb8000;
#define TXTWIDTH 80
#define TXTHEIGHT 25
#define BYTESPERCHAR 2

/* Define functions */

void clearScreen();
unsigned int printf(char *message, unsigned int line);

int main()
{
	clearScreen();
	printf("Hello, World", 1);
	for(;;)
		;
}

void clearScreen()	/* Clear the screen of text */
{
	/* We set a pointer to the video memory; we declare it char so we can write to it a byte at a time */
	char *vidmem = (char *) VIDMEMPTR;
	unsigned int i = 0;
	
	/* Write to the video memory to clear the screen */
	
	while( i < ( TXTWIDTH * TXTHEIGHT * BYTESPERCHAR ) )
	{
		vidmem[i] = ' ';	/* Set character to blank space */
		i++;
		vidmem[i] = WHITE_TEXT;	/* Set style to WHITE_TEXT */
		i++;
	}
	
}	/* (End clear screen function) */


unsigned int printf(char *message, unsigned int line) /* Prints a message at the given line */
{
	/* We set a pointer to the video memory; we declare it char so we can write to it a byte at a time */
	char *vidmem = (char *) VIDMEMPTR;

	unsigned int i = 0;
	i = ( line * TXTWIDTH * BYTESPERCHAR );

	
	while( *message != 0 )
		{
			vidmem[i] = *message;
			i++;
			vidmem[i] = WHITE_TEXT;
			i++;
			++message;
		}
	
	
	return 1;
	
}	/* End printf function */

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/* Link.ld -- Linker script for the kernel - ensure everything goes in the */
/*            Correct place.  */
/*            Original file taken from Bran's Kernel Development */
/*            tutorials: http://www.osdever.net/bkerndev/index.php. */

ENTRY(start)
SECTIONS
{
  .text 0x100000 :
  {
    code = .; _code = .; __code = .;
    *(.text)
    . = ALIGN(4096);
  }

  .data :
  {
     data = .; _data = .; __data = .;
     *(.data)
     *(.rodata)
     . = ALIGN(4096);
  }

  .bss :
  {
    bss = .; _bss = .; __bss = .;
    *(.bss)
    . = ALIGN(4096);
  }

  end = .; _end = .; __end = .;
}

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ENTRY(start)

SECTIONS
{
   . = 0x100000;

  START_ADDRESS = .;
  CODE_SECTION = .;

  .text :
  {
    *(.text)
  }

  . = ALIGN(4096);
  DATA_SECTION = .;

  .data :
  {
     *(.data)
     *(.rodata)
  }

   . = ALIGN(4096);
  BSS_SECTION = .;

  .bss :
  {
    *(.bss)
  }

  . = ALIGN(4096);
  END_ADDRESS = . ;
}

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char pStr[] = {'h','e','l','l','o','\0'};
printf("%s", pStr);

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	.file	"kernel.c"
	.text
	.p2align 4,,15
.globl putch
	.type	putch, @function
putch:
	pushl	%ebp
	movl	%esp, %ebp
	movl	12(%ebp), %eax
	movl	8(%ebp), %edx
	leal	(%eax,%eax,4), %eax
	sall	$4, %eax
	addl	16(%ebp), %eax
	movb	%dl, 753664(%eax,%eax)
	xorl	%eax, %eax
	popl	%ebp
	ret
	.size	putch, .-putch
	.p2align 4,,15
.globl clearScreen
	.type	clearScreen, @function
clearScreen:
	pushl	%ebp
	xorl	%eax, %eax
	movl	%esp, %ebp
	.p2align 4,,7
.L4:
	movb	$32, 753664(%eax)
	movb	$7, 753665(%eax)
	addl	$2, %eax
	cmpl	$4000, %eax
	jne	.L4
	popl	%ebp
	ret
	.size	clearScreen, .-clearScreen
	.p2align 4,,15
.globl printf
	.type	printf, @function
printf:
	pushl	%ebp
	movl	%esp, %ebp
	movl	8(%ebp), %edx
	movl	12(%ebp), %eax
	movzbl	(%edx), %ecx
	testb	%cl, %cl
	je	.L11
	leal	(%eax,%eax,4), %eax
	sall	$5, %eax
	.p2align 4,,7
.L13:
	movb	%cl, 753664(%eax)
	movb	$7, 753665(%eax)
	movzbl	1(%edx), %ecx
	addl	$2, %eax
	addl	$1, %edx
	testb	%cl, %cl
	jne	.L13
.L11:
	popl	%ebp
	movl	$1, %eax
	ret
	.size	printf, .-printf
	.section	.rodata.str1.1,"aMS",@progbits,1
.LC0:
	.string	"Hello, World"
	.text
	.p2align 4,,15
.globl main
	.type	main, @function
main:
	leal	4(%esp), %ecx
	andl	$-16, %esp
	pushl	-4(%ecx)
	pushl	%ebp
	movl	%esp, %ebp
	pushl	%ecx
	subl	$8, %esp
	call	clearScreen
	movl	$1, 4(%esp)
	movl	$.LC0, (%esp)
	call	printf
.L17:
	jmp	.L17
	.size	main, .-main
	.ident	"GCC: (GNU) 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)"
	.section	.note.GNU-stack,"",@progbits

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	.string	":"
.LC15:
	.string	", Len: "
.LC16:
	.string	", Type: "
.LC17:
	.string	", Size: "
.LC18:
	.string	" KiB"

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LC21:
	.ascii ", Size: \0"