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Diffstat (limited to 'Documentation/i386/boot.txt')
| -rw-r--r-- | Documentation/i386/boot.txt | 35 |
1 files changed, 22 insertions, 13 deletions
diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt index 1c48f0eba6f..10312bebe55 100644 --- a/Documentation/i386/boot.txt +++ b/Documentation/i386/boot.txt @@ -2,7 +2,7 @@ ---------------------------- H. Peter Anvin <hpa@zytor.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 /Size -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" below. -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 +this limit. 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.) +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: +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 |