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SubjectRe: [PATCH v6 19/27] x86, boot: update comments about entries for 64bit image
On Thu, Dec 13, 2012 at 3:27 PM, H. Peter Anvin <> wrote:
> if we depend on other
> things we should make that explicit, not just here but in boot.txt.

please check lines for boot.txt


**** 64-bit BOOT PROTOCOL

For machine with 64bit cpus and 64bit kernel, we could use 64bit bootloader
We need a 64-bit boot protocol.

In 64-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 under or above 4G 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 setting up the struct boot_params, the boot loader can load the
64-bit kernel in the same way as that of 16-bit boot protocol, but
kernel could be above 4G.

In 64-bit boot protocol, the kernel is started by jumping to the
64-bit kernel entry point, which is the start address of loaded
64-bit kernel plus 0x200.

At entry, the CPU must be in 64-bit mode with paging enabled.
The range with setup_header.init_size from start address of loaded
kernel and zero page and command line buffer get ident mapping;
a GDT must be loaded with the descriptors for selectors
__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat
segment; __BOOT_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; %rsi must hold the base
address of the struct boot_params.

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