Diffstat (limited to 'Documentation/i386/boot.txt')
1 files changed, 22 insertions, 13 deletions
diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt
index 1c48f0eba6f..10312bebe55 100644
@@ -2,7 +2,7 @@
H. Peter Anvin <email@example.com>
- Last update 2002-01-01
+ Last update 2005-09-02
On the i386 platform, the Linux kernel uses a rather complicated boot
convention. This has evolved partially due to historical aspects, as
@@ -34,6 +34,8 @@ Protocol 2.02: (Kernel 2.4.0-test3-pre3) New command line protocol.
Protocol 2.03: (Kernel 2.4.18-pre1) Explicitly makes the highest possible
initrd address available to the bootloader.
+Protocol 2.04: (Kernel 2.6.14) Extend the syssize field to four bytes.
**** MEMORY LAYOUT
@@ -103,10 +105,9 @@ The header looks like:
Offset Proto Name Meaning
-01F1/1 ALL setup_sects The size of the setup in sectors
+01F1/1 ALL(1 setup_sects The size of the setup in sectors
01F2/2 ALL root_flags If set, the root is mounted readonly
-01F4/2 ALL syssize DO NOT USE - for bootsect.S use only
-01F6/2 ALL swap_dev DO NOT USE - obsolete
+01F4/4 2.04+(2 syssize The size of the 32-bit code in 16-byte paras
01F8/2 ALL ram_size DO NOT USE - for bootsect.S use only
01FA/2 ALL vid_mode Video mode control
01FC/2 ALL root_dev Default root device number
@@ -129,8 +130,12 @@ Offset Proto Name Meaning
0228/4 2.02+ cmd_line_ptr 32-bit pointer to the kernel command line
022C/4 2.03+ initrd_addr_max Highest legal initrd address
-For backwards compatibility, if the setup_sects field contains 0, the
-real value is 4.
+(1) For backwards compatibility, if the setup_sects field contains 0, the
+ real value is 4.
+(2) For boot protocol prior to 2.04, the upper two bytes of the syssize
+ field are unusable, which means the size of a bzImage kernel
+ cannot be determined.
If the "HdrS" (0x53726448) magic number is not found at offset 0x202,
the boot protocol version is "old". Loading an old kernel, the
@@ -230,12 +235,16 @@ loader to communicate with the kernel. Some of its options are also
relevant to the boot loader itself, see "special command line options"
-The kernel command line is a null-terminated string up to 255
-characters long, plus the final null.
+The kernel command line is a null-terminated string currently up to
+255 characters long, plus the final null. A string that is too long
+will be automatically truncated by the kernel, a boot loader may allow
+a longer command line to be passed to permit future kernels to extend
If the boot protocol version is 2.02 or later, the address of the
kernel command line is given by the header field cmd_line_ptr (see
+above.) This address can be anywhere between the end of the setup
+heap and 0xA0000.
If the protocol version is *not* 2.02 or higher, the kernel
command line is entered using the following protocol:
@@ -255,7 +264,7 @@ command line is entered using the following protocol:
**** SAMPLE BOOT CONFIGURATION
As a sample configuration, assume the following layout of the real
+mode segment (this is a typical, and recommended layout):
0x0000-0x7FFF Real mode kernel
0x8000-0x8FFF Stack and heap
@@ -312,9 +321,9 @@ Such a boot loader should enter the following fields in the header:
**** LOADING THE REST OF THE KERNEL
-The non-real-mode kernel starts at offset (setup_sects+1)*512 in the
-kernel file (again, if setup_sects == 0 the real value is 4.) It
-should be loaded at address 0x10000 for Image/zImage kernels and
+The 32-bit (non-real-mode) kernel starts at offset (setup_sects+1)*512
+in the kernel file (again, if setup_sects == 0 the real value is 4.)
+It should be loaded at address 0x10000 for Image/zImage kernels and
0x100000 for bzImage kernels.
The kernel is a bzImage kernel if the protocol >= 2.00 and the 0x01