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authorRoy Franz <roy.franz@linaro.org>2013-09-22 22:45:25 (GMT)
committerMatt Fleming <matt.fleming@intel.com>2013-09-25 11:34:32 (GMT)
commit4172fe2f8a479e2237459918edc83b027efa8808 (patch)
tree8db815fdd21ffc767ac77e3701f54eb1465be9c6 /Documentation/x86
parent258f6fd738221766b512cd8c7120563b78d62829 (diff)
EFI stub documentation updates
Move efi-stub.txt out of x86 directory and into common directory in preparation for adding ARM EFI stub support. Signed-off-by: Roy Franz <roy.franz@linaro.org> Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Diffstat (limited to 'Documentation/x86')
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diff --git a/Documentation/x86/efi-stub.txt b/Documentation/x86/efi-stub.txt
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- The EFI Boot Stub
- ---------------------------
-
-On the x86 platform, a bzImage can masquerade as a PE/COFF image,
-thereby convincing EFI firmware loaders to load it as an EFI
-executable. The code that modifies the bzImage header, along with the
-EFI-specific entry point that the firmware loader jumps to are
-collectively known as the "EFI boot stub", and live in
-arch/x86/boot/header.S and arch/x86/boot/compressed/eboot.c,
-respectively.
-
-By using the EFI boot stub it's possible to boot a Linux kernel
-without the use of a conventional EFI boot loader, such as grub or
-elilo. Since the EFI boot stub performs the jobs of a boot loader, in
-a certain sense it *IS* the boot loader.
-
-The EFI boot stub is enabled with the CONFIG_EFI_STUB kernel option.
-
-
-**** How to install bzImage.efi
-
-The bzImage located in arch/x86/boot/bzImage must be copied to the EFI
-System Partiion (ESP) and renamed with the extension ".efi". Without
-the extension the EFI firmware loader will refuse to execute it. It's
-not possible to execute bzImage.efi from the usual Linux file systems
-because EFI firmware doesn't have support for them.
-
-
-**** Passing kernel parameters from the EFI shell
-
-Arguments to the kernel can be passed after bzImage.efi, e.g.
-
- fs0:> bzImage.efi console=ttyS0 root=/dev/sda4
-
-
-**** The "initrd=" option
-
-Like most boot loaders, the EFI stub allows the user to specify
-multiple initrd files using the "initrd=" option. This is the only EFI
-stub-specific command line parameter, everything else is passed to the
-kernel when it boots.
-
-The path to the initrd file must be an absolute path from the
-beginning of the ESP, relative path names do not work. Also, the path
-is an EFI-style path and directory elements must be separated with
-backslashes (\). For example, given the following directory layout,
-
-fs0:>
- Kernels\
- bzImage.efi
- initrd-large.img
-
- Ramdisks\
- initrd-small.img
- initrd-medium.img
-
-to boot with the initrd-large.img file if the current working
-directory is fs0:\Kernels, the following command must be used,
-
- fs0:\Kernels> bzImage.efi initrd=\Kernels\initrd-large.img
-
-Notice how bzImage.efi can be specified with a relative path. That's
-because the image we're executing is interpreted by the EFI shell,
-which understands relative paths, whereas the rest of the command line
-is passed to bzImage.efi.

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