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Taken from list archive at http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2001-July/004064.html

Initial definitions
-------------------

The following symbol definitions rely on you knowing the translation that
__virt_to_phys() does for your machine.  This macro converts the passed
virtual address to a physical address.  Normally, it is simply:

                phys = virt - PAGE_OFFSET + PHYS_OFFSET


Decompressor Symbols
--------------------

ZTEXTADDR
        Start address of decompressor.  There's no point in talking about
        virtual or physical addresses here, since the MMU will be off at
        the time when you call the decompressor code.  You normally call
        the kernel at this address to start it booting.  This doesn't have
        to be located in RAM, it can be in flash or other read-only or
        read-write addressable medium.

ZBSSADDR
        Start address of zero-initialised work area for the decompressor.
        This must be pointing at RAM.  The decompressor will zero initialise
        this for you.  Again, the MMU will be off.

ZRELADDR
        This is the address where the decompressed kernel will be written,
        and eventually executed.  The following constraint must be valid:

                __virt_to_phys(TEXTADDR) == ZRELADDR

        The initial part of the kernel is carefully coded to be position
        independent.

INITRD_PHYS
        Physical address to place the initial RAM disk.  Only relevant if
        you are using the bootpImage stuff (which only works on the old
        struct param_struct).

INITRD_VIRT
        Virtual address of the initial RAM disk.  The following  constraint
        must be valid:

                __virt_to_phys(INITRD_VIRT) == INITRD_PHYS

PARAMS_PHYS
        Physical address of the struct param_struct or tag list, giving the
        kernel various parameters about its execution environment.


Kernel Symbols
--------------

PHYS_OFFSET
        Physical start address of the first bank of RAM.

PAGE_OFFSET
        Virtual start address of the first bank of RAM.  During the kernel
        boot phase, virtual address PAGE_OFFSET will be mapped to physical
        address PHYS_OFFSET, along with any other mappings you supply.
        This should be the same value as TASK_SIZE.

TASK_SIZE
        The maximum size of a user process in bytes.  Since user space
        always starts at zero, this is the maximum address that a user
        process can access+1.  The user space stack grows down from this
        address.

        Any virtual address below TASK_SIZE is deemed to be user process
        area, and therefore managed dynamically on a process by process
        basis by the kernel.  I'll call this the user segment.

        Anything above TASK_SIZE is common to all processes.  I'll call
        this the kernel segment.

        (In other words, you can't put IO mappings below TASK_SIZE, and
        hence PAGE_OFFSET).

TEXTADDR
        Virtual start address of kernel, normally PAGE_OFFSET + 0x8000.
        This is where the kernel image ends up.  With the latest kernels,
        it must be located at 32768 bytes into a 128MB region.  Previous
        kernels placed a restriction of 256MB here.

DATAADDR
        Virtual address for the kernel data segment.  Must not be defined
        when using the decompressor.

VMALLOC_START
VMALLOC_END
        Virtual addresses bounding the vmalloc() area.  There must not be
        any static mappings in this area; vmalloc will overwrite them.
        The addresses must also be in the kernel segment (see above).
        Normally, the vmalloc() area starts VMALLOC_OFFSET bytes above the
        last virtual RAM address (found using variable high_memory).

VMALLOC_OFFSET
        Offset normally incorporated into VMALLOC_START to provide a hole
        between virtual RAM and the vmalloc area.  We do this to allow
        out of bounds memory accesses (eg, something writing off the end
        of the mapped memory map) to be caught.  Normally set to 8MB.

Architecture Specific Macros
----------------------------

BOOT_MEM(pram,pio,vio)
        `pram' specifies the physical start address of RAM.  Must always
        be present, and should be the same as PHYS_OFFSET.

        `pio' is the physical address of an 8MB region containing IO for
        use with the debugging macros in arch/arm/kernel/debug-armv.S.

        `vio' is the virtual address of the 8MB debugging region.

        It is expected that the debugging region will be re-initialised
        by the architecture specific code later in the code (via the
        MAPIO function).

BOOT_PARAMS
        Same as, and see PARAMS_PHYS.

FIXUP(func)
        Machine specific fixups, run before memory subsystems have been
        initialised.

MAPIO(func)
        Machine specific function to map IO areas (including the debug
        region above).

INITIRQ(func)
        Machine specific function to initialise interrupts.