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Diffstat (limited to 'Documentation/i386/boot.txt')
| -rw-r--r-- | Documentation/i386/boot.txt | 32 |
1 files changed, 22 insertions, 10 deletions
diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt index 66fa67fec2a..35985b34d5a 100644 --- a/Documentation/i386/boot.txt +++ b/Documentation/i386/boot.txt @@ -2,7 +2,7 @@ ---------------------------- H. Peter Anvin <hpa@zytor.com> - Last update 2007-05-16 + Last update 2007-05-23 On the i386 platform, the Linux kernel uses a rather complicated boot convention. This has evolved partially due to historical aspects, as @@ -202,6 +202,8 @@ All general purpose boot loaders should write the fields marked nonstandard address should fill in the fields marked (reloc); other boot loaders can ignore those fields. +The byte order of all fields is littleendian (this is x86, after all.) + Field name: setup_secs Type: read Offset/size: 0x1f1/1 @@ -280,14 +282,16 @@ Type: read Offset/size: 0x206/2 Protocol: 2.00+ - Contains the boot protocol version, e.g. 0x0204 for version 2.04. + Contains the boot protocol version, in (major << 8)+minor format, + e.g. 0x0204 for version 2.04, and 0x0a11 for a hypothetical version + 10.17. Field name: readmode_swtch Type: modify (optional) Offset/size: 0x208/4 Protocol: 2.00+ - Boot loader hook (see separate chapter.) + Boot loader hook (see ADVANCED BOOT LOADER HOOKS below.) Field name: start_sys Type: read @@ -304,10 +308,17 @@ Protocol: 2.00+ If set to a nonzero value, contains a pointer to a NUL-terminated human-readable kernel version number string, less 0x200. This can be used to display the kernel version to the user. This value - should be less than (0x200*setup_sects). For example, if this value - is set to 0x1c00, the kernel version number string can be found at - offset 0x1e00 in the kernel file. This is a valid value if and only - if the "setup_sects" field contains the value 14 or higher. + should be less than (0x200*setup_sects). + + For example, if this value is set to 0x1c00, the kernel version + number string can be found at offset 0x1e00 in the kernel file. + This is a valid value if and only if the "setup_sects" field + contains the value 15 or higher, as: + + 0x1c00 < 15*0x200 (= 0x1e00) but + 0x1c00 >= 14*0x200 (= 0x1c00) + + 0x1c00 >> 9 = 14, so the minimum value for setup_secs is 15. Field name: type_of_loader Type: write (obligatory) @@ -377,7 +388,7 @@ Protocol: 2.00+ This field can be modified for two purposes: - 1. as a boot loader hook (see separate chapter.) + 1. as a boot loader hook (see ADVANCED BOOT LOADER HOOKS below.) 2. if a bootloader which does not install a hook loads a relocatable kernel at a nonstandard address it will have to modify @@ -715,7 +726,7 @@ switched off, especially if the loaded kernel has the floppy driver as a demand-loaded module! -**** ADVANCED BOOT TIME HOOKS +**** ADVANCED BOOT LOADER HOOKS If the boot loader runs in a particularly hostile environment (such as LOADLIN, which runs under DOS) it may be impossible to follow the @@ -740,4 +751,5 @@ IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and set them up to BOOT_DS (0x18) yourself. After completing your hook, you should jump to the address - that was in this field before your boot loader overwrote it. + that was in this field before your boot loader overwrote it + (relocated, if appropriate.) |