x86: boot protocol updates

[sfrench/cifs-2.6.git] / Documentation / i386 / boot.txt

diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt
index 2f75e750e4f5c650a89df593ead1a1ff320eee62..2eb16100bb3fef7658799f5f7f4d259be644b537 100644 (file)
--- a/Documentation/i386/boot.txt
+++ b/Documentation/i386/boot.txt
@@ -170,6 +170,8 @@ Offset      Proto   Name            Meaning
 0238/4 2.06+   cmdline_size    Maximum size of the kernel command line
 023C/4 2.07+   hardware_subarch Hardware subarchitecture
 0240/8 2.07+   hardware_subarch_data Subarchitecture-specific data
+0248/4 2.08+   payload_offset  Offset of kernel payload
+024C/4 2.08+   payload_length  Length of kernel payload
 
 (1) For backwards compatibility, if the setup_sects field contains 0, the
     real value is 4.
@@ -512,6 +514,32 @@ Protocol:  2.07+
 
   A pointer to data that is specific to hardware subarch
 
+Field name:    payload_offset
+Type:          read
+Offset/size:   0x248/4
+Protocol:      2.08+
+
+  If non-zero then this field contains the offset from the end of the
+  real-mode code to the payload.
+
+  The payload may be compressed. The format of both the compressed and
+  uncompressed data should be determined using the standard magic
+  numbers. Currently only gzip compressed ELF is used.
+  
+Field name:    payload_length
+Type:          read
+Offset/size:   0x24c/4
+Protocol:      2.08+
+
+  The length of the payload.
+
+**** THE IMAGE CHECKSUM
+
+From boot protocol version 2.08 onwards the CRC-32 is calculated over
+the entire file using the characteristic polynomial 0x04C11DB7 and an
+initial remainder of 0xffffffff.  The checksum is appended to the
+file; therefore the CRC of the file up to the limit specified in the
+syssize field of the header is always 0.
 
 **** THE KERNEL COMMAND LINE
 
@@ -785,3 +813,41 @@ IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
        After completing your hook, you should jump to the address
        that was in this field before your boot loader overwrote it
        (relocated, if appropriate.)
+
+
+**** 32-bit BOOT PROTOCOL
+
+For machine with some new BIOS other than legacy BIOS, such as EFI,
+LinuxBIOS, etc, and kexec, the 16-bit real mode setup code in kernel
+based on legacy BIOS can not be used, so a 32-bit boot protocol needs
+to be defined.
+
+In 32-bit boot protocol, the first step in loading a Linux kernel
+should be to setup the boot parameters (struct boot_params,
+traditionally known as "zero page"). The memory for struct boot_params
+should be allocated and initialized to all zero. Then the setup header
+from offset 0x01f1 of kernel image on should be loaded into struct
+boot_params and examined. The end of setup header can be calculated as
+follow:
+
+       0x0202 + byte value at offset 0x0201
+
+In addition to read/modify/write the setup header of the struct
+boot_params as that of 16-bit boot protocol, the boot loader should
+also fill the additional fields of the struct boot_params as that
+described in zero-page.txt.
+
+After setupping the struct boot_params, the boot loader can load the
+32/64-bit kernel in the same way as that of 16-bit boot protocol.
+
+In 32-bit boot protocol, the kernel is started by jumping to the
+32-bit kernel entry point, which is the start address of loaded
+32/64-bit kernel.
+
+At entry, the CPU must be in 32-bit protected mode with paging
+disabled; a GDT must be loaded with the descriptors for selectors
+__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat
+segment; __BOOS_CS must have execute/read permission, and __BOOT_DS
+must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
+must be __BOOT_DS; interrupt must be disabled; %esi must hold the base
+address of the struct boot_params; %ebp, %edi and %ebx must be zero.