Bring this file into the documentation.
Signed-off-by: Simon Glass sjg@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@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@chromium.org 7-Oct-2014