Documentation/x86/boot.rst

4 The Linux/x86 Boot Protocol
14 Currently, the following versions of the Linux/x86 boot protocol exist.
20 Protocol 2.00	(Kernel 1.3.73) Added bzImage and initrd support, as
26 Protocol 2.01	(Kernel 1.3.76) Added a heap overrun warning.
28 Protocol 2.02	(Kernel 2.4.0-test3-pre3) New command line protocol.
35 Protocol 2.03	(Kernel 2.4.18-pre1) Explicitly makes the highest possible
38 Protocol 2.04	(Kernel 2.6.14) Extend the syssize field to four bytes.
40 Protocol 2.05	(Kernel 2.6.20) Make protected mode kernel relocatable.
43 Protocol 2.06	(Kernel 2.6.22) Added a field that contains the size of
46 Protocol 2.07	(Kernel 2.6.24) Added paravirtualised boot protocol.
50 Protocol 2.08	(Kernel 2.6.26) Added crc32 checksum and ELF format
54 Protocol 2.09	(Kernel 2.6.26) Added a field of 64-bit physical
57 Protocol 2.10	(Kernel 2.6.31) Added a protocol for relaxed alignment
61 Protocol 2.11	(Kernel 3.6) Added a field for offset of EFI handover
62 		protocol entry point.
64 Protocol 2.12	(Kernel 3.8) Added the xloadflags field and extension fields
68 Protocol 2.13	(Kernel 3.14) Support 32- and 64-bit flags being set in
72 Protocol 2.14	BURNT BY INCORRECT COMMIT
77 Protocol 2.15	(Kernel 5.5) Added the kernel_info and kernel_info.setup_type_max.
81      The protocol version number should be changed only if the setup header
84      xloadflags (in this case the protocol version number should not be
88      with great care. Starting from the protocol 2.15 the primary way to
125 the 2.02 protocol resolves that problem.
142 For a modern bzImage kernel with boot protocol version >= 2.02, a
198 0206/2		2.00+		version			Boot protocol version supported
203 0211/1		2.00+		loadflags		Boot protocol option flags
217 0236/2		2.12+		xloadflags		Boot protocol option flags
235   (2) For boot protocol prior to 2.04, the upper two bytes of the syssize
242 the boot protocol version is "old".  Loading an old kernel, the
249 Otherwise, the "version" field contains the protocol version,
250 e.g. protocol version 2.01 will contain 0x0201 in this field.  When
252 supported by the protocol version in use.
274 Protocol:	ALL
285 Protocol:	ALL
295 Offset/size:	0x1f4/4 (protocol 2.04+) 0x1f4/2 (protocol ALL)
296 Protocol:	2.04+
300   For protocol versions older than 2.04 this field is only two bytes
308 Protocol:	ALL
325 Protocol:	ALL
335 Protocol:	ALL
345 Protocol:	2.00+
356 Protocol:	2.00+
365 Protocol:	2.00+
368   Contains the boot protocol version, in (major << 8)+minor format,
376 Protocol:	2.00+
385 Protocol:	2.00+
394 Protocol:	2.00+
416 Protocol:	2.00+
466 Protocol:	2.00+
495 	Protocol: 2.07+
510 Protocol:	2.00-2.01
513   When using protocol 2.00 or 2.01, if the real mode kernel is not
521   This field is can be ignored when the protocol is 2.02 or higher, or
528 Protocol:	2.00+
547 Protocol:	2.00+
557 Protocol:	2.00+
567 Protocol:	2.00+
576 Protocol:	2.01+
586 Protocol:	2.02+
597   to write for protocol version 2.02 or higher.
603 Protocol:	2.02+
613   to write for protocol version 2.02 or higher.
619 Protocol:	2.02+
631   the 2.02+ protocol.
637 Protocol:	2.03+
651 Protocol:	2.05+ (read), 2.10+ (modify)
659   Starting with protocol version 2.10, this reflects the kernel
668 Protocol:	2.05+
680 Protocol:	2.10+
698 Protocol:	2.12+
730 Protocol:	2.06+
735   cmdline_size characters. With protocol version 2.05 and earlier, the
742 Protocol:	2.07+
764 Protocol:	2.07+
775 Protocol:	2.08+
793 Protocol:	2.08+
802 Protocol:	2.09+
834   protocol 2.15::
872 Protocol:	2.10+
909   the EFI handover protocol entry point. Boot loaders using the EFI
910   handover protocol to boot the kernel should jump to this offset.
912   See EFI HANDOVER PROTOCOL below for more details.
918 Protocol:	2.15+
949 without revising the boot protocol entirely, breaking backwards compatibility.
1033 From boot protocol version 2.08 onwards the CRC-32 is calculated over
1049 length can be retrieved from the field cmdline_size.  Before protocol
1053 If the boot protocol version is 2.02 or later, the address of the
1058 If the protocol version is *not* 2.02 or higher, the kernel
1059 command line is entered using the following protocol:
1088 	- When loading a 2.01 or earlier boot protocol kernel.
1093      relocated to 0x90000.  For the "old" protocol, the
1098 For boot protocol 2.02 or higher, the command line does not have to be
1121     When loading at 0x90000 OR the protocol version is 2.01 or earlier:
1137 	if ( protocol >= 0x0200 ) {
1144 		if ( protocol >= 0x0202 && loadflags & 0x01 )
1149 		if ( protocol >= 0x0201 ) {
1154 		if ( protocol >= 0x0202 ) {
1196 The kernel is a bzImage kernel if the protocol >= 2.00 and the 0x01
1199 	is_bzImage = (protocol >= 0x0200) && (loadflags & 0x01);
1274 	/* Note: in the case of the "old" kernel protocol, base_ptr must
1325 32-bit Boot Protocol
1330 based on legacy BIOS can not be used, so a 32-bit boot protocol needs
1333 In 32-bit boot protocol, the first step in loading a Linux kernel
1344 boot_params as that of 16-bit boot protocol, the boot loader should
1349 32/64-bit kernel in the same way as that of 16-bit boot protocol.
1351 In 32-bit boot protocol, the kernel is started by jumping to the
1363 64-bit Boot Protocol
1367 and we need a 64-bit boot protocol.
1369 In 64-bit boot protocol, the first step in loading a Linux kernel
1380 boot_params as that of 16-bit boot protocol, the boot loader should
1385 64-bit kernel in the same way as that of 16-bit boot protocol, but
1388 In 64-bit boot protocol, the kernel is started by jumping to the
1402 EFI Handover Protocol (deprecated)
1405 This protocol allows boot loaders to defer initialisation to the EFI
1407 from the boot media and jump to the EFI handover protocol entry point
1434 NOTE: The EFI Handover Protocol is deprecated in favour of the ordinary PE/COFF
1436       loading protocol (refer to [0] for an example of the bootloader side of