Commit 8ee2f2df authored by Yinghai Lu's avatar Yinghai Lu Committed by H. Peter Anvin

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: default avatarYinghai 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: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent ee92d815
...@@ -1054,6 +1054,44 @@ must have read/write permission; CS must be __BOOT_CS and DS, ES, SS ...@@ -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 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. 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.
**** EFI HANDOVER PROTOCOL **** EFI HANDOVER PROTOCOL
This protocol allows boot loaders to defer initialisation to the EFI This protocol allows boot loaders to defer initialisation to the EFI
......
...@@ -37,6 +37,12 @@ ...@@ -37,6 +37,12 @@
__HEAD __HEAD
.code32 .code32
ENTRY(startup_32) ENTRY(startup_32)
/*
* 32bit entry is 0 and it is ABI so immutable!
* If we come here directly from a bootloader,
* kernel(text+data+bss+brk) ramdisk, zero_page, command line
* all need to be under the 4G limit.
*/
cld cld
/* /*
* Test KEEP_SEGMENTS flag to see if the bootloader is asking * Test KEEP_SEGMENTS flag to see if the bootloader is asking
...@@ -182,20 +188,18 @@ ENTRY(startup_32) ...@@ -182,20 +188,18 @@ ENTRY(startup_32)
lret lret
ENDPROC(startup_32) ENDPROC(startup_32)
/*
* Be careful here startup_64 needs to be at a predictable
* address so I can export it in an ELF header. Bootloaders
* should look at the ELF header to find this address, as
* it may change in the future.
*/
.code64 .code64
.org 0x200 .org 0x200
ENTRY(startup_64) ENTRY(startup_64)
/* /*
* 64bit entry is 0x200 and it is ABI so immutable!
* We come here either from startup_32 or directly from a * We come here either from startup_32 or directly from a
* 64bit bootloader. If we come here from a bootloader we depend on * 64bit bootloader.
* an identity mapped page table being provied that maps our * If we come here from a bootloader, kernel(text+data+bss+brk),
* entire text+data+bss and hopefully all of memory. * ramdisk, zero_page, command line could be above 4G.
* We depend on an identity mapped page table being provided
* that maps our entire kernel(text+data+bss+brk), zero page
* and command line.
*/ */
#ifdef CONFIG_EFI_STUB #ifdef CONFIG_EFI_STUB
/* /*
......
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