path: root/Documentation/x86
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authorYinghai Lu <yinghai@kernel.org>2013-01-24 12:20:07 -0800
committerH. Peter Anvin <hpa@linux.intel.com>2013-01-29 19:32:57 -0800
commit8ee2f2dfdbdfe1851fcc0191b2d4faa4c26a39fb (patch)
tree01032cfcd27238ac44a3447ca4d07c4685bdb359 /Documentation/x86
parentee92d815027a76ef92f3ec7b155b0c8aa345f239 (diff)
x86, boot: Update comments about entries for 64bit image
Now 64bit entry is fixed on 0x200, can not be changed anymore. Update the comments to reflect that. Also put info about it in boot.txt -v2: fix some grammar error Signed-off-by: Yinghai Lu <yinghai@kernel.org> Link: http://lkml.kernel.org/r/1359058816-7615-27-git-send-email-yinghai@kernel.org Cc: Rob Landley <rob@landley.net> Cc: Matt Fleming <matt.fleming@intel.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'Documentation/x86')
1 files changed, 38 insertions, 0 deletions
diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index 3edb4c2887a1..0e383169839a 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -1054,6 +1054,44 @@ 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.
+**** 64-bit BOOT PROTOCOL
+For machine with 64bit cpus and 64bit kernel, we could use 64bit bootloader
+and 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
+could be allocated anywhere (even above 4G) and initialized to all zero.
+Then, the setup header at offset 0x01f1 of kernel image on should be
+loaded into struct boot_params and examined. The end of setup header
+can be calculated as follows:
+ 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 described
+in zero-page.txt.
+After setting up the struct boot_params, the boot loader can load
+64-bit kernel in the same way as that of 16-bit boot protocol, but
+kernel could be loaded 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.
This protocol allows boot loaders to defer initialisation to the EFI

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