path: root/Documentation/x86
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authorLinus Torvalds <torvalds@linux-foundation.org>2012-07-26 13:13:25 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-07-26 13:13:25 -0700
commit0a2fe19ccc4bc552a8083a595a3aa737b8bea727 (patch)
tree3bed37182f95fa3ac1673530457e994a89bd7e26 /Documentation/x86
parentc1b669b72a05aeae0882742dd40f30d51732ed15 (diff)
parent9ca8f72a9297f2052d806bd1111e176533aa69bd (diff)
Merge branch 'x86-efi-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pul x86/efi changes from Ingo Molnar: "This tree adds an EFI bootloader handover protocol, which, once supported on the bootloader side, will make bootup faster and might result in simpler bootloaders. The other change activates the EFI wall clock time accessors on x86-64 as well, instead of the legacy RTC readout." * 'x86-efi-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86, efi: Handover Protocol x86-64/efi: Use EFI to deal with platform wall clock
Diffstat (limited to 'Documentation/x86')
1 files changed, 41 insertions, 0 deletions
diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index 473b32fd544e..9efceff51bfb 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -54,6 +54,9 @@ Protocol 2.10: (Kernel 2.6.31) Added a protocol for relaxed alignment
beyond the kernel_alignment added, new init_size and
pref_address fields. Added extended boot loader IDs.
+Protocol 2.11: (Kernel 3.6) Added a field for offset of EFI handover
+ protocol entry point.
The traditional memory map for the kernel loader, used for Image or
@@ -189,6 +192,7 @@ Offset Proto Name Meaning
of struct setup_data
0258/8 2.10+ pref_address Preferred loading address
0260/4 2.10+ init_size Linear memory required during initialization
+0264/4 2.11+ handover_offset Offset of handover entry point
(1) For backwards compatibility, if the setup_sects field contains 0, the
real value is 4.
@@ -693,6 +697,16 @@ Offset/size: 0x260/4
runtime_start = pref_address
+Field name: handover_offset
+Type: read
+Offset/size: 0x264/4
+ This field is the offset from the beginning of the kernel image to
+ the EFI handover protocol entry point. Boot loaders using the EFI
+ handover protocol to boot the kernel should jump to this offset.
+ See EFI HANDOVER PROTOCOL below for more details.
@@ -1013,3 +1027,30 @@ 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.
+This protocol allows boot loaders to defer initialisation to the EFI
+boot stub. The boot loader is required to load the kernel/initrd(s)
+from the boot media and jump to the EFI handover protocol entry point
+which is hdr->handover_offset bytes from the beginning of
+The function prototype for the handover entry point looks like this,
+ efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp)
+'handle' is the EFI image handle passed to the boot loader by the EFI
+firmware, 'table' is the EFI system table - these are the first two
+arguments of the "handoff state" as described in section 2.3 of the
+UEFI specification. 'bp' is the boot loader-allocated boot params.
+The boot loader *must* fill out the following fields in bp,
+ o hdr.code32_start
+ o hdr.cmd_line_ptr
+ o hdr.cmdline_size
+ o hdr.ramdisk_image (if applicable)
+ o hdr.ramdisk_size (if applicable)
+All other fields should be zero.

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