patch-2.1.125 linux/Documentation/i386/zero-page.txt

• Lines: 74
• Date: Mon Oct 5 12:59:25 1998
• Orig file: v2.1.124/linux/Documentation/i386/zero-page.txt
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.1.124/linux/Documentation/i386/zero-page.txt linux/Documentation/i386/zero-page.txt
@@ -0,0 +1,73 @@
+Summary of empty_zero_page layout (kernel point of view)
+     ( collected by Hans Lermen and Martin Mares )
+ 
+The contents of empty_zero_page are used to pass parameters from the
+16-bit realmode code of the kernel to the 32-bit part. References/settings
+to it mainly are in:
+
+  arch/i386/boot/setup.S
+  arch/i386/boot/video.S
+  arch/i386/kernel/head.S
+  arch/i386/kernel/setup.c
+ 
+
+Offset	Type		Description
+------  ----		-----------
+    0	32 bytes	struct screen_info, SCREEN_INFO
+			ATTENTION, overlaps the following !!!
+    2	unsigned short	EXT_MEM_K, extended memory size in Kb (from int 0x15)
+ 0x20	unsigned short	CL_MAGIC, commandline magic number (=0xA33F)
+ 0x22	unsigned short	CL_OFFSET, commandline offset
+			Address of commandline is calculated:
+			  0x90000 + contents of CL_OFFSET
+			(only taken, when CL_MAGIC = 0xA33F)
+ 0x40	20 bytes	struct apm_bios_info, APM_BIOS_INFO
+ 0x80	16 bytes	hd0-disk-parameter from intvector 0x41
+ 0x90	16 bytes	hd1-disk-parameter from intvector 0x46
+
+ 0xa0	16 bytes	System description table truncated to 16 bytes.
+			( struct sys_desc_table_struct )
+ 0xb0 - 0x1df		Free. Add more parameters here if you really need them.
+
+0x1e0	unsigned long	ALT_MEM_K, alternative mem check, in Kb
+0x1f1	char		size of setup.S, number of sectors
+0x1f2	unsigned short	MOUNT_ROOT_RDONLY (if !=0)
+0x1f4	unsigned short	size of compressed kernel-part in the
+			(b)zImage-file (in 16 byte units, rounded up)
+0x1f6	unsigned short	swap_dev (unused AFAIK)
+0x1f8	unsigned short	RAMDISK_FLAGS
+0x1fa	unsigned short	VGA-Mode (old one)
+0x1fc	unsigned short	ORIG_ROOT_DEV (high=Major, low=minor)
+0x1ff	char		AUX_DEVICE_INFO
+
+0x200	short jump to start of setup code aka "reserved" field.
+0x202	4 bytes		Signature for SETUP-header, ="HdrS"
+0x206	unsigned short	Version number of header format
+			Current version is 0x0201...
+0x208	8 bytes		(used by setup.S for communication with boot loaders,
+			 look there)
+0x210	char		LOADER_TYPE, = 0, old one
+			else it is set by the loader:
+			0xTV: T=0 for LILO
+				1 for Loadlin
+				2 for bootsect-loader
+				3 for SYSLINUX
+				4 for ETHERBOOT
+				V = version
+0x211	char		loadflags:
+			bit0 = 1: kernel is loaded high (bzImage)
+			bit7 = 1: Heap and pointer (see below) set by boot
+				  loader.
+0x212	unsigned short	(setup.S)
+0x214	unsigned long	KERNEL_START, where the loader started the kernel
+0x218	unsigned long	INITRD_START, address of loaded ramdisk image
+0x21c	unsigned long	INITRD_SIZE, size in bytes of ramdisk image
+0x220	4 bytes		(setup.S)
+0x224	unsigned short	setup.S heap end pointer
+0x226 - 0x7ff		setup.S code.
+
+0x800	string, 2K max	COMMAND_LINE, the kernel commandline as
+			copied using CL_OFFSET.
+			Note: this will be copied once more by setup.c
+			into a local buffer which is only 256 bytes long.
+			( #define COMMAND_LINE_SIZE 256 )