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-rw-r--r--Documentation/x86/boot.rst21
1 files changed, 18 insertions, 3 deletions
diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
index fa7ddc0428c8..5325c71ca877 100644
--- a/Documentation/x86/boot.rst
+++ b/Documentation/x86/boot.rst
@@ -1399,8 +1399,8 @@ 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 (deprecated)
+==================================
This protocol allows boot loaders to defer initialisation to the EFI
boot stub. The boot loader is required to load the kernel/initrd(s)
@@ -1408,6 +1408,12 @@ from the boot media and jump to the EFI handover protocol entry point
which is hdr->handover_offset bytes from the beginning of
startup_{32,64}.
+The boot loader MUST respect the kernel's PE/COFF metadata when it comes
+to section alignment, the memory footprint of the executable image beyond
+the size of the file itself, and any other aspect of the PE/COFF header
+that may affect correct operation of the image as a PE/COFF binary in the
+execution context provided by the EFI firmware.
+
The function prototype for the handover entry point looks like this::
efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp)
@@ -1419,9 +1425,18 @@ UEFI specification. 'bp' is the boot loader-allocated boot params.
The boot loader *must* fill out the following fields in bp::
- - hdr.code32_start
- hdr.cmd_line_ptr
- hdr.ramdisk_image (if applicable)
- hdr.ramdisk_size (if applicable)
All other fields should be zero.
+
+NOTE: The EFI Handover Protocol is deprecated in favour of the ordinary PE/COFF
+ entry point, combined with the LINUX_EFI_INITRD_MEDIA_GUID based initrd
+ loading protocol (refer to [0] for an example of the bootloader side of
+ this), which removes the need for any knowledge on the part of the EFI
+ bootloader regarding the internal representation of boot_params or any
+ requirements/limitations regarding the placement of the command line
+ and ramdisk in memory, or the placement of the kernel image itself.
+
+[0] https://github.com/u-boot/u-boot/commit/ec80b4735a593961fe701cc3a5d717d4739b0fd0