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authorH. Peter Anvin <hpa@zytor.com>2009-05-08 03:54:11 +0400
committerH. Peter Anvin <hpa@zytor.com>2009-05-12 04:45:06 +0400
commit5031296c57024a78ddad4edfc993367dbf4abb98 (patch)
tree7506daf7aabf25a5ec567fcd2e644fe22cd91eca /Documentation/x86
parentfe83fcc0a14dcf71996de5eb84771b2369ba7abc (diff)
downloadlinux-5031296c57024a78ddad4edfc993367dbf4abb98.tar.xz
x86: add extension fields for bootloader type and version
A long ago, in days of yore, it all began with a god named Thor. There were vikings and boats and some plans for a Linux kernel header. Unfortunately, a single 8-bit field was used for bootloader type and version. This has generally worked without *too* much pain, but we're getting close to flat running out of ID fields. Add extension fields for both type and version. The type will be extended if it the old field is 0xE; the version is a simple MSB extension. Keep /proc/sys/kernel/bootloader_type containing (type << 4) + (ver & 0xf) for backwards compatiblity, but also add /proc/sys/kernel/bootloader_version which contains the full version number. [ Impact: new feature to support more bootloaders ] Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'Documentation/x86')
-rw-r--r--Documentation/x86/boot.txt59
1 files changed, 52 insertions, 7 deletions
diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index cf8dfc70a118..8da3a795083f 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -50,10 +50,9 @@ Protocol 2.08: (Kernel 2.6.26) Added crc32 checksum and ELF format
Protocol 2.09: (Kernel 2.6.26) Added a field of 64-bit physical
pointer to single linked list of struct setup_data.
-Protocol 2.10: (Kernel 2.6.31) A protocol for relaxed alignment
+Protocol 2.10: (Kernel 2.6.31) Added a protocol for relaxed alignment
beyond the kernel_alignment added, new init_size and
- pref_address fields.
-
+ pref_address fields. Added extended boot loader IDs.
**** MEMORY LAYOUT
@@ -173,7 +172,8 @@ Offset Proto Name Meaning
021C/4 2.00+ ramdisk_size initrd size (set by boot loader)
0220/4 2.00+ bootsect_kludge DO NOT USE - for bootsect.S use only
0224/2 2.01+ heap_end_ptr Free memory after setup end
-0226/2 N/A pad1 Unused
+0226/1 2.02+(3 ext_loader_ver Extended boot loader version
+0227/1 2.02+(3 ext_loader_type Extended boot loader ID
0228/4 2.02+ cmd_line_ptr 32-bit pointer to the kernel command line
022C/4 2.03+ ramdisk_max Highest legal initrd address
0230/4 2.05+ kernel_alignment Physical addr alignment required for kernel
@@ -197,6 +197,8 @@ Offset Proto Name Meaning
field are unusable, which means the size of a bzImage kernel
cannot be determined.
+(3) Ignored, but safe to set, for boot protocols 2.02-2.09.
+
If the "HdrS" (0x53726448) magic number is not found at offset 0x202,
the boot protocol version is "old". Loading an old kernel, the
following parameters should be assumed:
@@ -350,18 +352,32 @@ Protocol: 2.00+
0xTV here, where T is an identifier for the boot loader and V is
a version number. Otherwise, enter 0xFF here.
+ For boot loader IDs above T = 0xD, write T = 0xE to this field and
+ write the extended ID minus 0x10 to the ext_loader_type field.
+ Similarly, the ext_loader_ver field can be used to provide more than
+ four bits for the bootloader version.
+
+ For example, for T = 0x15, V = 0x234, write:
+
+ type_of_loader <- 0xE4
+ ext_loader_type <- 0x05
+ ext_loader_ver <- 0x23
+
Assigned boot loader ids:
0 LILO (0x00 reserved for pre-2.00 bootloader)
1 Loadlin
2 bootsect-loader (0x20, all other values reserved)
- 3 SYSLINUX
- 4 EtherBoot
+ 3 Syslinux
+ 4 Etherboot/gPXE
5 ELILO
7 GRUB
- 8 U-BOOT
+ 8 U-Boot
9 Xen
A Gujin
B Qemu
+ C Arcturus Networks uCbootloader
+ E Extended (see ext_loader_type)
+ F Special (0xFF = undefined)
Please contact <hpa@zytor.com> if you need a bootloader ID
value assigned.
@@ -460,6 +476,35 @@ Protocol: 2.01+
Set this field to the offset (from the beginning of the real-mode
code) of the end of the setup stack/heap, minus 0x0200.
+Field name: ext_loader_ver
+Type: write (optional)
+Offset/size: 0x226/1
+Protocol: 2.02+
+
+ This field is used as an extension of the version number in the
+ type_of_loader field. The total version number is considered to be
+ (type_of_loader & 0x0f) + (ext_loader_ver << 4).
+
+ The use of this field is boot loader specific. If not written, it
+ is zero.
+
+ Kernels prior to 2.6.31 did not recognize this field, but it is safe
+ to write for protocol version 2.02 or higher.
+
+Field name: ext_loader_type
+Type: write (obligatory if (type_of_loader & 0xf0) == 0xe0)
+Offset/size: 0x227/1
+Protocol: 2.02+
+
+ This field is used as an extension of the type number in
+ type_of_loader field. If the type in type_of_loader is 0xE, then
+ the actual type is (ext_loader_type + 0x10).
+
+ This field is ignored if the type in type_of_loader is not 0xE.
+
+ Kernels prior to 2.6.31 did not recognize this field, but it is safe
+ to write for protocol version 2.02 or higher.
+
Field name: cmd_line_ptr
Type: write (obligatory)
Offset/size: 0x228/4