linux-imx

             THE LINUX/x86 BOOT PROTOCOL

             ---------------------------

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On the x86 platform, the Linux kernel uses a rather complicated boot

convention.  This has evolved partially due to historical aspects, as

well as the desire in the early days to have the kernel itself be a

bootable image, the complicated PC memory model and due to changed

expectations in the PC industry caused by the effective demise of

real-mode DOS as a mainstream operating system.

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Currently, the following versions of the Linux/x86 boot protocol exist.

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Old kernels:    zImage/Image support only.  Some very early kernels

        may not even support a command line.

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Protocol 2.00:  (Kernel 1.3.73) Added bzImage and initrd support, as

        well as a formalized way to communicate between the

        boot loader and the kernel.  setup.S made relocatable,

        although the traditional setup area still assumed

        writable.

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Protocol 2.01:  (Kernel 1.3.76) Added a heap overrun warning.

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Protocol 2.02:  (Kernel 2.4.0-test3-pre3) New command line protocol.

        Lower the conventional memory ceiling.  No overwrite

        of the traditional setup area, thus making booting

        safe for systems which use the EBDA from SMM or 32-bit

        BIOS entry points.  zImage deprecated but still

        supported.

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Protocol 2.03:  (Kernel 2.4.18-pre1) Explicitly makes the highest possible

        initrd address available to the bootloader.

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Protocol 2.04:  (Kernel 2.6.14) Extend the syssize field to four bytes.

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Protocol 2.05:  (Kernel 2.6.20) Make protected mode kernel relocatable.

        Introduce relocatable_kernel and kernel_alignment fields.

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Protocol 2.06:  (Kernel 2.6.22) Added a field that contains the size of

        the boot command line.

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Protocol 2.07:  (Kernel 2.6.24) Added paravirtualised boot protocol.

        Introduced hardware_subarch and hardware_subarch_data

        and KEEP_SEGMENTS flag in load_flags.

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Protocol 2.08:  (Kernel 2.6.26) Added crc32 checksum and ELF format

        payload. Introduced payload_offset and payload_length

        fields to aid in locating the payload.

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Protocol 2.09:  (Kernel 2.6.26) Added a field of 64-bit physical

        pointer to single linked list of struct setup_data.

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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.

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Protocol 2.11:  (Kernel 3.6) Added a field for offset of EFI handover

        protocol entry point.

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Protocol 2.12:  (Kernel 3.8) Added the xloadflags field and extension fields

        to struct boot_params for loading bzImage and ramdisk

        above 4G in 64bit.

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**** MEMORY LAYOUT

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The traditional memory map for the kernel loader, used for Image or

zImage kernels, typically looks like:

​

    |            |

0A0000  +------------------------+

    |  Reserved for BIOS     |  Do not use.  Reserved for BIOS EBDA.

09A000  +------------------------+

    |  Command line      |

    |  Stack/heap        |  For use by the kernel real-mode code.

098000  +------------------------+  

    |  Kernel setup      |  The kernel real-mode code.

090200  +------------------------+

    |  Kernel boot sector    |  The kernel legacy boot sector.

090000  +------------------------+

    |  Protected-mode kernel |  The bulk of the kernel image.

010000  +------------------------+

    |  Boot loader       |  <- Boot sector entry point 0000:7C00

001000  +------------------------+

    |  Reserved for MBR/BIOS |

000800  +------------------------+

    |  Typically used by MBR |

000600  +------------------------+ 

    |  BIOS use only     |

000000  +------------------------+

​

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When using bzImage, the protected-mode kernel was relocated to