[PATCH v2 05/14] doc: Bring in FIT x86 boot
Simon Glass
sjg at chromium.org
Fri Jun 23 14:22:05 CEST 2023
Bring this file into the documentation.
Signed-off-by: Simon Glass <sjg at chromium.org>
---
(no changes since v1)
doc/uImage.FIT/x86-fit-boot.txt | 272 --------------------------------
doc/usage/fit/index.rst | 1 +
doc/usage/fit/x86-fit-boot.rst | 269 +++++++++++++++++++++++++++++++
3 files changed, 270 insertions(+), 272 deletions(-)
delete mode 100644 doc/uImage.FIT/x86-fit-boot.txt
create mode 100644 doc/usage/fit/x86-fit-boot.rst
diff --git a/doc/uImage.FIT/x86-fit-boot.txt b/doc/uImage.FIT/x86-fit-boot.txt
deleted file mode 100644
index 88d3460a83eb..000000000000
--- a/doc/uImage.FIT/x86-fit-boot.txt
+++ /dev/null
@@ -1,272 +0,0 @@
-Booting Linux on x86 with FIT
-=============================
-
-Background
-----------
-
-(corrections to the text below are welcome)
-
-Generally Linux x86 uses its own very complex booting method. There is a setup
-binary which contains all sorts of parameters and a compressed self-extracting
-binary for the kernel itself, often with a small built-in serial driver to
-display decompression progress.
-
-The x86 CPU has various processor modes. I am no expert on these, but my
-understanding is that an x86 CPU (even a really new one) starts up in a 16-bit
-'real' mode where only 1MB of memory is visible, moves to 32-bit 'protected'
-mode where 4GB is visible (or more with special memory access techniques) and
-then to 64-bit 'long' mode if 64-bit execution is required.
-
-Partly the self-extracting nature of Linux was introduced to cope with boot
-loaders that were barely capable of loading anything. Even changing to 32-bit
-mode was something of a challenge, so putting this logic in the kernel seemed
-to make sense.
-
-Bit by bit more and more logic has been added to this post-boot pre-Linux
-wrapper:
-
-- Changing to 32-bit mode
-- Decompression
-- Serial output (with drivers for various chips)
-- Load address randomisation
-- Elf loader complete with relocation (for the above)
-- Random number generator via 3 methods (again for the above)
-- Some sort of EFI mini-loader (1000+ glorious lines of code)
-- Locating and tacking on a device tree and ramdisk
-
-To my mind, if you sit back and look at things from first principles, this
-doesn't make a huge amount of sense. Any boot loader worth its salts already
-has most of the above features and more besides. The boot loader already knows
-the layout of memory, has a serial driver, can decompress things, includes an
-ELF loader and supports device tree and ramdisks. The decision to duplicate
-all these features in a Linux wrapper caters for the lowest common
-denominator: a boot loader which consists of a BIOS call to load something off
-disk, followed by a jmp instruction.
-
-(Aside: On ARM systems, we worry that the boot loader won't know where to load
-the kernel. It might be easier to just provide that information in the image,
-or in the boot loader rather than adding a self-relocator to put it in the
-right place. Or just use ELF?
-
-As a result, the x86 kernel boot process is needlessly complex. The file
-format is also complex, and obfuscates the contents to a degree that it is
-quite a challenge to extract anything from it. This bzImage format has become
-so prevalent that is actually isn't possible to produce the 'raw' kernel build
-outputs with the standard Makefile (as it is on ARM for example, at least at
-the time of writing).
-
-This document describes an alternative boot process which uses simple raw
-images which are loaded into the right place by the boot loader and then
-executed.
-
-
-Build the kernel
-----------------
-
-Note: these instructions assume a 32-bit kernel. U-Boot also supports directly
-booting a 64-bit kernel by jumping into 64-bit mode first (see below).
-
-You can build the kernel as normal with 'make'. This will create a file called
-'vmlinux'. This is a standard ELF file and you can look at it if you like:
-
-$ objdump -h vmlinux
-
-vmlinux: file format elf32-i386
-
-Sections:
-Idx Name Size VMA LMA File off Algn
- 0 .text 00416850 81000000 01000000 00001000 2**5
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
- 1 .notes 00000024 81416850 01416850 00417850 2**2
- CONTENTS, ALLOC, LOAD, READONLY, CODE
- 2 __ex_table 00000c50 81416880 01416880 00417880 2**3
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 3 .rodata 00154b9e 81418000 01418000 00419000 2**5
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 4 __bug_table 0000597c 8156cba0 0156cba0 0056dba0 2**0
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 5 .pci_fixup 00001b80 8157251c 0157251c 0057351c 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 6 .tracedata 00000024 8157409c 0157409c 0057509c 2**0
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 7 __ksymtab 00007ec0 815740c0 015740c0 005750c0 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 8 __ksymtab_gpl 00004a28 8157bf80 0157bf80 0057cf80 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 9 __ksymtab_strings 0001d6fc 815809a8 015809a8 005819a8 2**0
- CONTENTS, ALLOC, LOAD, READONLY, DATA
- 10 __init_rodata 00001c3c 8159e0a4 0159e0a4 0059f0a4 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 11 __param 00000ff0 8159fce0 0159fce0 005a0ce0 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 12 __modver 00000330 815a0cd0 015a0cd0 005a1cd0 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 13 .data 00063000 815a1000 015a1000 005a2000 2**12
- CONTENTS, ALLOC, LOAD, RELOC, DATA
- 14 .init.text 0002f104 81604000 01604000 00605000 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
- 15 .init.data 00040cdc 81634000 01634000 00635000 2**12
- CONTENTS, ALLOC, LOAD, RELOC, DATA
- 16 .x86_cpu_dev.init 0000001c 81674cdc 01674cdc 00675cdc 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 17 .altinstructions 0000267c 81674cf8 01674cf8 00675cf8 2**0
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 18 .altinstr_replacement 00000942 81677374 01677374 00678374 2**0
- CONTENTS, ALLOC, LOAD, READONLY, CODE
- 19 .iommu_table 00000014 81677cb8 01677cb8 00678cb8 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 20 .apicdrivers 00000004 81677cd0 01677cd0 00678cd0 2**2
- CONTENTS, ALLOC, LOAD, RELOC, DATA
- 21 .exit.text 00001a80 81677cd8 01677cd8 00678cd8 2**0
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
- 22 .data..percpu 00007880 8167a000 0167a000 0067b000 2**12
- CONTENTS, ALLOC, LOAD, RELOC, DATA
- 23 .smp_locks 00003000 81682000 01682000 00683000 2**2
- CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
- 24 .bss 000a1000 81685000 01685000 00686000 2**12
- ALLOC
- 25 .brk 00424000 81726000 01726000 00686000 2**0
- ALLOC
- 26 .comment 00000049 00000000 00000000 00686000 2**0
- CONTENTS, READONLY
- 27 .GCC.command.line 0003e055 00000000 00000000 00686049 2**0
- CONTENTS, READONLY
- 28 .debug_aranges 0000f4c8 00000000 00000000 006c40a0 2**3
- CONTENTS, RELOC, READONLY, DEBUGGING
- 29 .debug_info 0440b0df 00000000 00000000 006d3568 2**0
- CONTENTS, RELOC, READONLY, DEBUGGING
- 30 .debug_abbrev 0022a83b 00000000 00000000 04ade647 2**0
- CONTENTS, READONLY, DEBUGGING
- 31 .debug_line 004ead0d 00000000 00000000 04d08e82 2**0
- CONTENTS, RELOC, READONLY, DEBUGGING
- 32 .debug_frame 0010a960 00000000 00000000 051f3b90 2**2
- CONTENTS, RELOC, READONLY, DEBUGGING
- 33 .debug_str 001b442d 00000000 00000000 052fe4f0 2**0
- CONTENTS, READONLY, DEBUGGING
- 34 .debug_loc 007c7fa9 00000000 00000000 054b291d 2**0
- CONTENTS, RELOC, READONLY, DEBUGGING
- 35 .debug_ranges 00098828 00000000 00000000 05c7a8c8 2**3
- CONTENTS, RELOC, READONLY, DEBUGGING
-
-There is also the setup binary mentioned earlier. This is at
-arch/x86/boot/setup.bin and is about 12KB in size. It includes the command
-line and various settings need by the kernel. Arguably the boot loader should
-provide all of this also, but setting it up is some complex that the kernel
-helps by providing a head start.
-
-As you can see the code loads to address 0x01000000 and everything else
-follows after that. We could load this image using the 'bootelf' command but
-we would still need to provide the setup binary. This is not supported by
-U-Boot although I suppose you could mostly script it. This would permit the
-use of a relocatable kernel.
-
-All we need to boot is the vmlinux file and the setup.bin file.
-
-
-Create a FIT
-------------
-
-To create a FIT you will need a source file describing what should go in the
-FIT. See kernel.its for an example for x86 and also instructions on setting
-the 'arch' value for booting 64-bit kernels if desired. Put this into a file
-called image.its.
-
-Note that setup is loaded to the special address of 0x90000 (a special address
-you just have to know) and the kernel is loaded to 0x01000000 (the address you
-saw above). This means that you will need to load your FIT to a different
-address so that U-Boot doesn't overwrite it when decompressing. Something like
-0x02000000 will do so you can set CONFIG_SYS_LOAD_ADDR to that.
-
-In that example the kernel is compressed with lzo. Also we need to provide a
-flat binary, not an ELF. So the steps needed to set things are are:
-
- # Create a flat binary
- objcopy -O binary vmlinux vmlinux.bin
-
- # Compress it into LZO format
- lzop vmlinux.bin
-
- # Build a FIT image
- mkimage -f image.its image.fit
-
-(be careful to run the mkimage from your U-Boot tools directory since it
-will have x86_setup support.)
-
-You can take a look at the resulting fit file if you like:
-
-$ dumpimage -l image.fit
-FIT description: Simple image with single Linux kernel on x86
-Created: Tue Oct 7 10:57:24 2014
- Image 0 (kernel)
- Description: Vanilla Linux kernel
- Created: Tue Oct 7 10:57:24 2014
- Type: Kernel Image
- Compression: lzo compressed
- Data Size: 4591767 Bytes = 4484.15 kB = 4.38 MB
- Architecture: Intel x86
- OS: Linux
- Load Address: 0x01000000
- Entry Point: 0x00000000
- Hash algo: sha1
- Hash value: 446b5163ebfe0fb6ee20cbb7a8501b263cd92392
- Image 1 (setup)
- Description: Linux setup.bin
- Created: Tue Oct 7 10:57:24 2014
- Type: x86 setup.bin
- Compression: uncompressed
- Data Size: 12912 Bytes = 12.61 kB = 0.01 MB
- Hash algo: sha1
- Hash value: a1f2099cf47ff9816236cd534c77af86e713faad
- Default Configuration: 'config-1'
- Configuration 0 (config-1)
- Description: Boot Linux kernel
- Kernel: kernel
-
-
-Booting the FIT
----------------
-
-To make it boot you need to load it and then use 'bootm' to boot it. A
-suitable script to do this from a network server is:
-
- bootp
- tftp image.fit
- bootm
-
-This will load the image from the network and boot it. The command line (from
-the 'bootargs' environment variable) will be passed to the kernel.
-
-If you want a ramdisk you can add it as normal with FIT. If you want a device
-tree then x86 doesn't normally use those - it has ACPI instead.
-
-
-Why Bother?
------------
-
-1. It demystifies the process of booting an x86 kernel
-2. It allows use of the standard U-Boot boot file format
-3. It allows U-Boot to perform decompression - problems will provide an error
-message and you are still in the boot loader. It is possible to investigate.
-4. It avoids all the pre-loader code in the kernel which is quite complex to
-follow
-5. You can use verified/secure boot and other features which haven't yet been
-added to the pre-Linux
-6. It makes x86 more like other architectures in the way it boots a kernel.
-You can potentially use the same file format for the kernel, and the same
-procedure for building and packaging it.
-
-
-References
-----------
-
-In the Linux kernel, Documentation/x86/boot.txt defines the boot protocol for
-the kernel including the setup.bin format. This is handled in U-Boot in
-arch/x86/lib/zimage.c and arch/x86/lib/bootm.c.
-
-Various files in the same directory as this file describe the FIT format.
-
-
---
-Simon Glass
-sjg at chromium.org
-7-Oct-2014
diff --git a/doc/usage/fit/index.rst b/doc/usage/fit/index.rst
index 93a962319035..0635d06b811a 100644
--- a/doc/usage/fit/index.rst
+++ b/doc/usage/fit/index.rst
@@ -11,3 +11,4 @@ doc/uImage.FIT
:maxdepth: 1
source_file_format
+ x86-fit-boot
diff --git a/doc/usage/fit/x86-fit-boot.rst b/doc/usage/fit/x86-fit-boot.rst
new file mode 100644
index 000000000000..93b73bb90192
--- /dev/null
+++ b/doc/usage/fit/x86-fit-boot.rst
@@ -0,0 +1,269 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Booting Linux on x86 with FIT
+=============================
+
+Background
+----------
+
+Generally Linux x86 uses its own very complex booting method. There is a setup
+binary which contains all sorts of parameters and a compressed self-extracting
+binary for the kernel itself, often with a small built-in serial driver to
+display decompression progress.
+
+The x86 CPU has various processor modes. I am no expert on these, but my
+understanding is that an x86 CPU (even a really new one) starts up in a 16-bit
+'real' mode where only 1MB of memory is visible, moves to 32-bit 'protected'
+mode where 4GB is visible (or more with special memory access techniques) and
+then to 64-bit 'long' mode if 64-bit execution is required.
+
+Partly the self-extracting nature of Linux was introduced to cope with boot
+loaders that were barely capable of loading anything. Even changing to 32-bit
+mode was something of a challenge, so putting this logic in the kernel seemed
+to make sense.
+
+Bit by bit more and more logic has been added to this post-boot pre-Linux
+wrapper:
+
+- Changing to 32-bit mode
+- Decompression
+- Serial output (with drivers for various chips)
+- Load address randomisation
+- Elf loader complete with relocation (for the above)
+- Random number generator via 3 methods (again for the above)
+- Some sort of EFI mini-loader (1000+ glorious lines of code)
+- Locating and tacking on a device tree and ramdisk
+
+To my mind, if you sit back and look at things from first principles, this
+doesn't make a huge amount of sense. Any boot loader worth its salts already
+has most of the above features and more besides. The boot loader already knows
+the layout of memory, has a serial driver, can decompress things, includes an
+ELF loader and supports device tree and ramdisks. The decision to duplicate
+all these features in a Linux wrapper caters for the lowest common
+denominator: a boot loader which consists of a BIOS call to load something off
+disk, followed by a jmp instruction.
+
+(Aside: On ARM systems, we worry that the boot loader won't know where to load
+the kernel. It might be easier to just provide that information in the image,
+or in the boot loader rather than adding a self-relocator to put it in the
+right place. Or just use ELF?
+
+As a result, the x86 kernel boot process is needlessly complex. The file
+format is also complex, and obfuscates the contents to a degree that it is
+quite a challenge to extract anything from it. This bzImage format has become
+so prevalent that is actually isn't possible to produce the 'raw' kernel build
+outputs with the standard Makefile (as it is on ARM for example, at least at
+the time of writing).
+
+This document describes an alternative boot process which uses simple raw
+images which are loaded into the right place by the boot loader and then
+executed.
+
+
+Build the kernel
+----------------
+
+Note: these instructions assume a 32-bit kernel. U-Boot also supports directly
+booting a 64-bit kernel by jumping into 64-bit mode first (see below).
+
+You can build the kernel as normal with 'make'. This will create a file called
+'vmlinux'. This is a standard ELF file and you can look at it if you like::
+
+ $ objdump -h vmlinux
+
+ vmlinux: file format elf32-i386
+
+ Sections:
+ Idx Name Size VMA LMA File off Algn
+ 0 .text 00416850 81000000 01000000 00001000 2**5
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
+ 1 .notes 00000024 81416850 01416850 00417850 2**2
+ CONTENTS, ALLOC, LOAD, READONLY, CODE
+ 2 __ex_table 00000c50 81416880 01416880 00417880 2**3
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 3 .rodata 00154b9e 81418000 01418000 00419000 2**5
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 4 __bug_table 0000597c 8156cba0 0156cba0 0056dba0 2**0
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 5 .pci_fixup 00001b80 8157251c 0157251c 0057351c 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 6 .tracedata 00000024 8157409c 0157409c 0057509c 2**0
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 7 __ksymtab 00007ec0 815740c0 015740c0 005750c0 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 8 __ksymtab_gpl 00004a28 8157bf80 0157bf80 0057cf80 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 9 __ksymtab_strings 0001d6fc 815809a8 015809a8 005819a8 2**0
+ CONTENTS, ALLOC, LOAD, READONLY, DATA
+ 10 __init_rodata 00001c3c 8159e0a4 0159e0a4 0059f0a4 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 11 __param 00000ff0 8159fce0 0159fce0 005a0ce0 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 12 __modver 00000330 815a0cd0 015a0cd0 005a1cd0 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 13 .data 00063000 815a1000 015a1000 005a2000 2**12
+ CONTENTS, ALLOC, LOAD, RELOC, DATA
+ 14 .init.text 0002f104 81604000 01604000 00605000 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
+ 15 .init.data 00040cdc 81634000 01634000 00635000 2**12
+ CONTENTS, ALLOC, LOAD, RELOC, DATA
+ 16 .x86_cpu_dev.init 0000001c 81674cdc 01674cdc 00675cdc 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 17 .altinstructions 0000267c 81674cf8 01674cf8 00675cf8 2**0
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 18 .altinstr_replacement 00000942 81677374 01677374 00678374 2**0
+ CONTENTS, ALLOC, LOAD, READONLY, CODE
+ 19 .iommu_table 00000014 81677cb8 01677cb8 00678cb8 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 20 .apicdrivers 00000004 81677cd0 01677cd0 00678cd0 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, DATA
+ 21 .exit.text 00001a80 81677cd8 01677cd8 00678cd8 2**0
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
+ 22 .data..percpu 00007880 8167a000 0167a000 0067b000 2**12
+ CONTENTS, ALLOC, LOAD, RELOC, DATA
+ 23 .smp_locks 00003000 81682000 01682000 00683000 2**2
+ CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
+ 24 .bss 000a1000 81685000 01685000 00686000 2**12
+ ALLOC
+ 25 .brk 00424000 81726000 01726000 00686000 2**0
+ ALLOC
+ 26 .comment 00000049 00000000 00000000 00686000 2**0
+ CONTENTS, READONLY
+ 27 .GCC.command.line 0003e055 00000000 00000000 00686049 2**0
+ CONTENTS, READONLY
+ 28 .debug_aranges 0000f4c8 00000000 00000000 006c40a0 2**3
+ CONTENTS, RELOC, READONLY, DEBUGGING
+ 29 .debug_info 0440b0df 00000000 00000000 006d3568 2**0
+ CONTENTS, RELOC, READONLY, DEBUGGING
+ 30 .debug_abbrev 0022a83b 00000000 00000000 04ade647 2**0
+ CONTENTS, READONLY, DEBUGGING
+ 31 .debug_line 004ead0d 00000000 00000000 04d08e82 2**0
+ CONTENTS, RELOC, READONLY, DEBUGGING
+ 32 .debug_frame 0010a960 00000000 00000000 051f3b90 2**2
+ CONTENTS, RELOC, READONLY, DEBUGGING
+ 33 .debug_str 001b442d 00000000 00000000 052fe4f0 2**0
+ CONTENTS, READONLY, DEBUGGING
+ 34 .debug_loc 007c7fa9 00000000 00000000 054b291d 2**0
+ CONTENTS, RELOC, READONLY, DEBUGGING
+ 35 .debug_ranges 00098828 00000000 00000000 05c7a8c8 2**3
+ CONTENTS, RELOC, READONLY, DEBUGGING
+
+There is also the setup binary mentioned earlier. This is at
+arch/x86/boot/setup.bin and is about 12KB in size. It includes the command
+line and various settings need by the kernel. Arguably the boot loader should
+provide all of this also, but setting it up is some complex that the kernel
+helps by providing a head start.
+
+As you can see the code loads to address 0x01000000 and everything else
+follows after that. We could load this image using the 'bootelf' command but
+we would still need to provide the setup binary. This is not supported by
+U-Boot although I suppose you could mostly script it. This would permit the
+use of a relocatable kernel.
+
+All we need to boot is the vmlinux file and the setup.bin file.
+
+
+Create a FIT
+------------
+
+To create a FIT you will need a source file describing what should go in the
+FIT. See kernel.its for an example for x86 and also instructions on setting
+the 'arch' value for booting 64-bit kernels if desired. Put this into a file
+called image.its.
+
+Note that setup is loaded to the special address of 0x90000 (a special address
+you just have to know) and the kernel is loaded to 0x01000000 (the address you
+saw above). This means that you will need to load your FIT to a different
+address so that U-Boot doesn't overwrite it when decompressing. Something like
+0x02000000 will do so you can set CONFIG_SYS_LOAD_ADDR to that.
+
+In that example the kernel is compressed with lzo. Also we need to provide a
+flat binary, not an ELF. So the steps needed to set things are are::
+
+ # Create a flat binary
+ objcopy -O binary vmlinux vmlinux.bin
+
+ # Compress it into LZO format
+ lzop vmlinux.bin
+
+ # Build a FIT image
+ mkimage -f image.its image.fit
+
+(be careful to run the mkimage from your U-Boot tools directory since it
+will have x86_setup support.)
+
+You can take a look at the resulting fit file if you like::
+
+ $ dumpimage -l image.fit
+ FIT description: Simple image with single Linux kernel on x86
+ Created: Tue Oct 7 10:57:24 2014
+ Image 0 (kernel)
+ Description: Vanilla Linux kernel
+ Created: Tue Oct 7 10:57:24 2014
+ Type: Kernel Image
+ Compression: lzo compressed
+ Data Size: 4591767 Bytes = 4484.15 kB = 4.38 MB
+ Architecture: Intel x86
+ OS: Linux
+ Load Address: 0x01000000
+ Entry Point: 0x00000000
+ Hash algo: sha1
+ Hash value: 446b5163ebfe0fb6ee20cbb7a8501b263cd92392
+ Image 1 (setup)
+ Description: Linux setup.bin
+ Created: Tue Oct 7 10:57:24 2014
+ Type: x86 setup.bin
+ Compression: uncompressed
+ Data Size: 12912 Bytes = 12.61 kB = 0.01 MB
+ Hash algo: sha1
+ Hash value: a1f2099cf47ff9816236cd534c77af86e713faad
+ Default Configuration: 'config-1'
+ Configuration 0 (config-1)
+ Description: Boot Linux kernel
+ Kernel: kernel
+
+
+Booting the FIT
+---------------
+
+To make it boot you need to load it and then use 'bootm' to boot it. A
+suitable script to do this from a network server is::
+
+ bootp
+ tftp image.fit
+ bootm
+
+This will load the image from the network and boot it. The command line (from
+the 'bootargs' environment variable) will be passed to the kernel.
+
+If you want a ramdisk you can add it as normal with FIT. If you want a device
+tree then x86 doesn't normally use those - it has ACPI instead.
+
+
+Why Bother?
+-----------
+
+#. It demystifies the process of booting an x86 kernel
+#. It allows use of the standard U-Boot boot file format
+#. It allows U-Boot to perform decompression - problems will provide an error
+ message and you are still in the boot loader. It is possible to investigate.
+#. It avoids all the pre-loader code in the kernel which is quite complex to
+ follow
+#. You can use verified/secure boot and other features which haven't yet been
+ added to the pre-Linux
+#. It makes x86 more like other architectures in the way it boots a kernel.
+ You can potentially use the same file format for the kernel, and the same
+ procedure for building and packaging it.
+
+
+References
+----------
+
+In the Linux kernel, Documentation/x86/boot.txt defines the boot protocol for
+the kernel including the setup.bin format. This is handled in U-Boot in
+arch/x86/lib/zimage.c and arch/x86/lib/bootm.c.
+
+Various files in the same directory as this file describe the FIT format.
+
+
+.. sectionauthor:: Simon Glass <sjg at chromium.org> 7-Oct-2014
--
2.41.0.162.gfafddb0af9-goog
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