/Documentation/i386/zero-page.txt

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  1. Summary of boot_params layout (kernel point of view)
    2. 

  2.      ( collected by Hans Lermen and Martin Mares )
    3. 

  3.  
    4. 

  4. The contents of boot_params are used to pass parameters from the
    5. 

  5. 16-bit realmode code of the kernel to the 32-bit part. References/settings
    6. 

  6. to it mainly are in:
    7. 

  7. 

  8.   arch/i386/boot/setup.S
    9. 

  9.   arch/i386/boot/video.S
    10. 

  10.   arch/i386/kernel/head.S
    11. 

  11.   arch/i386/kernel/setup.c
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  12.  
    13. 

  13. 

  14. Offset	Type		Description
    15. 

  15. ------  ----		-----------
    16. 

  16.     0	32 bytes	struct screen_info, SCREEN_INFO
    17. 

  17. 			ATTENTION, overlaps the following !!!
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  18.     2	unsigned short	EXT_MEM_K, extended memory size in Kb (from int 0x15)
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  19.  0x20	unsigned short	CL_MAGIC, commandline magic number (=0xA33F)
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  20.  0x22	unsigned short	CL_OFFSET, commandline offset
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  21. 			Address of commandline is calculated:
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  22. 			  0x90000 + contents of CL_OFFSET
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  23. 			(only taken, when CL_MAGIC = 0xA33F)
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  24.  0x40	20 bytes	struct apm_bios_info, APM_BIOS_INFO
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  25.  0x60	16 bytes	Intel SpeedStep (IST) BIOS support information
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  26.  0x80	16 bytes	hd0-disk-parameter from intvector 0x41
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  27.  0x90	16 bytes	hd1-disk-parameter from intvector 0x46
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  28. 

  29.  0xa0	16 bytes	System description table truncated to 16 bytes.
    30. 

  30. 			( struct sys_desc_table_struct )
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  31.  0xb0 - 0x13f		Free. Add more parameters here if you really need them.
    32. 

  32.  0x140- 0x1be		EDID_INFO Video mode setup
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  33. 

  34. 0x1c4	unsigned long	EFI system table pointer
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  35. 0x1c8	unsigned long	EFI memory descriptor size
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  36. 0x1cc	unsigned long	EFI memory descriptor version
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  37. 0x1d0	unsigned long	EFI memory descriptor map pointer
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  38. 0x1d4	unsigned long	EFI memory descriptor map size
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  39. 0x1e0	unsigned long	ALT_MEM_K, alternative mem check, in Kb
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  40. 0x1e8	char		number of entries in E820MAP (below)
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  41. 0x1e9	unsigned char	number of entries in EDDBUF (below)
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  42. 0x1ea	unsigned char	number of entries in EDD_MBR_SIG_BUFFER (below)
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  43. 0x1f1	char		size of setup.S, number of sectors
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  44. 0x1f2	unsigned short	MOUNT_ROOT_RDONLY (if !=0)
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  45. 0x1f4	unsigned short	size of compressed kernel-part in the
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  46. 			(b)zImage-file (in 16 byte units, rounded up)
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  47. 0x1f6	unsigned short	swap_dev (unused AFAIK)
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  48. 0x1f8	unsigned short	RAMDISK_FLAGS
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  49. 0x1fa	unsigned short	VGA-Mode (old one)
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  50. 0x1fc	unsigned short	ORIG_ROOT_DEV (high=Major, low=minor)
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  51. 0x1ff	char		AUX_DEVICE_INFO
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  52. 

  53. 0x200	short jump to start of setup code aka "reserved" field.
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  54. 0x202	4 bytes		Signature for SETUP-header, ="HdrS"
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  55. 0x206	unsigned short	Version number of header format
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  56. 			Current version is 0x0201...
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  57. 0x208	8 bytes		(used by setup.S for communication with boot loaders,
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  58. 			 look there)
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  59. 0x210	char		LOADER_TYPE, = 0, old one
    60. 

  60. 			else it is set by the loader:
    61. 

  61. 			0xTV: T=0 for LILO
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  62. 				1 for Loadlin
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  63. 				2 for bootsect-loader
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  64. 				3 for SYSLINUX
    65. 

  65. 				4 for ETHERBOOT
    66. 

  66. 				V = version
    67. 

  67. 0x211	char		loadflags:
    68. 

  68. 			bit0 = 1: kernel is loaded high (bzImage)
    69. 

  69. 			bit7 = 1: Heap and pointer (see below) set by boot
    70. 

  70. 				  loader.
    71. 

  71. 0x212	unsigned short	(setup.S)
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  72. 0x214	unsigned long	KERNEL_START, where the loader started the kernel
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  73. 0x218	unsigned long	INITRD_START, address of loaded ramdisk image
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  74. 0x21c	unsigned long	INITRD_SIZE, size in bytes of ramdisk image
    75. 

  75. 0x220	4 bytes		(setup.S)
    76. 

  76. 0x224	unsigned short	setup.S heap end pointer
    77. 

  77. 0x226   unsigned short	zero_pad
    78. 

  78. 0x228   unsigned long	cmd_line_ptr
    79. 

  79. 0x22c   unsigned long	ramdisk_max
    80. 

  80. 0x230   16 bytes 	trampoline
    81. 

  81. 0x290 - 0x2cf		EDD_MBR_SIG_BUFFER (edd.S)
    82. 

  82. 0x2d0 - 0x600		E820MAP
    83. 

  83. 0x600 - 0x7ff		EDDBUF (edd.S) for disk signature read sector
    84. 

  84. 0x600 - 0x7eb		EDDBUF (edd.S) for edd data
    85.