Kernel: Add framebuffer information to kernel image

Framebuffer information is no longer hard coded into bootloader.
Kernel can define framebuffer info structure in its memory which is
used for finding proper video mode.

bootloader/bios/boot.S

@@ -60,8 +60,6 @@ stage2_main:
 	call get_memory_map
 	call read_user_command_line
 
-	call vesa_find_video_mode
-
 	call print_newline
 
 	movw $start_kernel_load_msg, %si
@@ -84,7 +82,7 @@ stage2_main:
 
 	call elf_read_kernel_to_memory
 
-	call vesa_set_target_mode
+	call vesa_set_video_mode
 
 	cli
 

bootloader/bios/framebuffer.S

@@ -1,20 +1,72 @@
-.set TARGET_WIDTH,	800
-.set TARGET_HEIGHT,	600
-.set TARGET_BPP,	32
-
 .code16
 .section .stage2
 
-# Find suitable video mode
+# kernel framebuffer information format
+#	.align 8
+#	.long 0xBABAB007
+#	.long -(0xBABAB007 + width + height + bpp)
+#	.long width		(2 bytes used, 4 bytes for ease of calculation)
+#	.long height	(2 bytes used, 4 bytes for ease of calculation)
+#	.long bpp		(1 bytes used, 4 bytes for ease of calculation)
+
+# scan memory 0x100000 -> 0x200000 for framebuffer information
 # return:
-#	ax: video mode number if found, 0 otherwise
-.global vesa_find_video_mode
+#	ax: target width
+#	bx: target height
+#	cx: target bpp
+vesa_scan_kernel_image:
+	pushl %edx
+	pushl %esi
+
+	movl $0x100000, %esi
+
+ .vesa_scan_kernel_image_loop:
+	# check magic
+	cmpl $0xBABAB007, (%esi)
+	jne .vesa_scan_kernel_image_next_addr
+
+	# check checksum
+	movl 0x00(%esi), %edx
+	addl 0x04(%esi), %edx
+	addl 0x08(%esi), %edx
+	addl 0x0C(%esi), %edx
+	addl 0x10(%esi), %edx
+	testl %edx, %edx
+	jnz .vesa_scan_kernel_image_next_addr
+
+	# set return registers
+	movw 0x08(%esi), %ax
+	movw 0x0C(%esi), %bx
+	movw 0x10(%esi), %cx
+	jmp .vesa_scan_kernel_image_done
+
+ .vesa_scan_kernel_image_next_addr:
+	addl $8, %esi
+	cmpl $0x200000, %esi
+	jb .vesa_scan_kernel_image_loop
+
+	# zero out return registers
+	xorw %ax, %ax
+	xorw %bx, %bx
+	xorw %cx, %cx
+
+ .vesa_scan_kernel_image_done:
+	popl %esi
+	popl %edx
+	ret
+
+# Find suitable video mode and save it in (vesa_target_mode)
 vesa_find_video_mode:
 	pushw %ax
+	pushw %bx
 	pushw %cx
 	pushw %di
 	pushl %esi
 
+	pushl %ebp
+	movl %esp, %ebp
+	subl $6, %esp
+
 	# clear target mode and frame buffer
 	movw $0, (vesa_target_mode)
 	movl $0, (framebuffer + 0)
@@ -23,6 +75,15 @@ vesa_find_video_mode:
 	movl $0, (framebuffer + 12)
 	movw $0, (framebuffer + 16)
 
+	call vesa_scan_kernel_image
+	testw %ax, %ax
+	jz .vesa_find_video_mode_loop_modes_done
+
+	# save arguments in stack
+	movw %ax, -2(%ebp)
+	movw %bx, -4(%ebp)
+	movw %cx, -6(%ebp)
+
 	# get vesa information
 	movw $0x4F00, %ax
 	movw $vesa_info_buffer, %di
@@ -57,21 +118,24 @@ vesa_find_video_mode:
 	jz .vesa_find_video_mode_next_mode
 
 	# compare mode's dimensions
-	cmpw $TARGET_WIDTH, (vesa_mode_info_buffer + 0x12)
+	movw -2(%ebp), %ax; cmpw %ax, (vesa_mode_info_buffer + 0x12)
 	jne .vesa_find_video_mode_next_mode
-	cmpw $TARGET_HEIGHT, (vesa_mode_info_buffer + 0x14)
+	movw -4(%ebp), %ax; cmpw %ax, (vesa_mode_info_buffer + 0x14)
 	jne .vesa_find_video_mode_next_mode
-	cmpb $TARGET_BPP, (vesa_mode_info_buffer + 0x19)
+	movb -6(%ebp), %al; cmpb %al, (vesa_mode_info_buffer + 0x19)
 	jne .vesa_find_video_mode_next_mode
 
+	# set address, pitch, type
 	movl (vesa_mode_info_buffer + 0x28), %esi
-	movl %esi,				(framebuffer + 0)
+	movl %esi, (framebuffer + 0)
 	movw (vesa_mode_info_buffer + 0x10), %ax
-	movw %ax,				(framebuffer + 4)
-	movl $TARGET_WIDTH,		(framebuffer + 8)
-	movl $TARGET_HEIGHT,	(framebuffer + 12)
-	movb $TARGET_BPP,		(framebuffer + 16)
-	movb $1,				(framebuffer + 17)
+	movw %ax,  (framebuffer + 4)
+	movb $1,   (framebuffer + 17)
+
+	# set width, height, bpp
+	movw -2(%ebp), %ax; movw %ax, (framebuffer +  8)
+	movw -4(%ebp), %ax; movw %ax, (framebuffer + 12)
+	movw -6(%ebp), %ax; movb %al, (framebuffer + 16)
 
 	movw %cx, (vesa_target_mode)
 	jmp .vesa_find_video_mode_loop_modes_done
@@ -81,9 +145,11 @@ vesa_find_video_mode:
 	jmp .vesa_find_video_mode_loop_modes
 
  .vesa_find_video_mode_loop_modes_done:
+	leavel
 	popl %esi
 	popw %di
 	popw %cx
+	popw %bx
 	popw %ax
 	ret
 
@@ -98,13 +164,16 @@ vesa_find_video_mode:
 	jmp print_and_halt
 
 
-# set mode found from vesa_find_video_mode. if no mode
-# was found, set it to 80x25 text mode to clear the screen.
-.global vesa_set_target_mode
-vesa_set_target_mode:
+# scan for video mode in kernel memory and set the correct one.
+# when video mode is not found or does not exists,
+# set it to 80x25 text mode to clear the screen.
+.global vesa_set_video_mode
+vesa_set_video_mode:
 	pushw %ax
 	pushw %bx
 
+	call vesa_find_video_mode
+
 	movw (vesa_target_mode), %bx
 	testw %bx, %bx
 	jz .vesa_set_target_mode_generic

kernel/arch/x86_64/boot.S

@@ -2,6 +2,10 @@
 .set PG_READ_WRITE,	1<<1
 .set PG_PAGE_SIZE,	1<<7
 
+.set FB_WIDTH,	800
+.set FB_HEIGHT,	600
+.set FB_BPP,	32
+
 #define KERNEL_OFFSET 0xFFFFFFFF80000000
 #define V2P(vaddr) ((vaddr) - KERNEL_OFFSET)
 
@@ -9,8 +13,8 @@
 
 # multiboot2 header
 .section .multiboot, "aw"
-multiboot2_start:
 	.align 8
+multiboot2_start:
 	.long 0xE85250D6
 	.long 0
 	.long multiboot2_end - multiboot2_start
@@ -21,9 +25,9 @@ multiboot2_start:
 	.short 5
 	.short 0
 	.long 20
-	.long 800
-	.long 600
-	.long 32
+	.long FB_WIDTH
+	.long FB_HEIGHT
+	.long FB_BPP
 
 	# legacy start
 	.align 8
@@ -38,6 +42,16 @@ multiboot2_start:
 	.long 8
 multiboot2_end:
 
+.section .bananboot, "aw"
+	.align 8
+bananboot_start:
+	.long 0xBABAB007
+	.long -(0xBABAB007 + FB_WIDTH + FB_HEIGHT + FB_BPP)
+	.long FB_WIDTH
+	.long FB_HEIGHT
+	.long FB_BPP
+bananboot_end:
+
 .section .bss, "aw", @nobits
  	# Create stack
 	.global g_boot_stack_bottom

kernel/arch/x86_64/linker.ld

@@ -11,6 +11,7 @@ SECTIONS
 	{
 		g_kernel_execute_start = .;
 		*(.multiboot)
+		*(.bananboot)
 		*(.text.*)
 	}
 	.userspace ALIGN(4K) : AT(ADDR(.userspace) - KERNEL_OFFSET)