=======
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Porting
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=======
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Taken from list archive at http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2001-July/004064.html
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Initial definitions
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-------------------
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The following symbol definitions rely on you knowing the translation that
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__virt_to_phys() does for your machine. This macro converts the passed
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virtual address to a physical address. Normally, it is simply:
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phys = virt - PAGE_OFFSET + PHYS_OFFSET
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Decompressor Symbols
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--------------------
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ZTEXTADDR
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Start address of decompressor. There's no point in talking about
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virtual or physical addresses here, since the MMU will be off at
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the time when you call the decompressor code. You normally call
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the kernel at this address to start it booting. This doesn't have
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to be located in RAM, it can be in flash or other read-only or
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read-write addressable medium.
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ZBSSADDR
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Start address of zero-initialised work area for the decompressor.
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This must be pointing at RAM. The decompressor will zero initialise
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this for you. Again, the MMU will be off.
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ZRELADDR
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This is the address where the decompressed kernel will be written,
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and eventually executed. The following constraint must be valid:
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__virt_to_phys(TEXTADDR) == ZRELADDR
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The initial part of the kernel is carefully coded to be position
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independent.
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INITRD_PHYS
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Physical address to place the initial RAM disk. Only relevant if
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you are using the bootpImage stuff (which only works on the old
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struct param_struct).
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INITRD_VIRT
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Virtual address of the initial RAM disk. The following constraint
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must be valid:
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__virt_to_phys(INITRD_VIRT) == INITRD_PHYS
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PARAMS_PHYS
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Physical address of the struct param_struct or tag list, giving the
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kernel various parameters about its execution environment.
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Kernel Symbols
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--------------
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PHYS_OFFSET
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Physical start address of the first bank of RAM.
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PAGE_OFFSET
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Virtual start address of the first bank of RAM. During the kernel
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boot phase, virtual address PAGE_OFFSET will be mapped to physical
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address PHYS_OFFSET, along with any other mappings you supply.
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This should be the same value as TASK_SIZE.
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TASK_SIZE
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The maximum size of a user process in bytes. Since user space
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always starts at zero, this is the maximum address that a user
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process can access+1. The user space stack grows down from this
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address.
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Any virtual address below TASK_SIZE is deemed to be user process
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area, and therefore managed dynamically on a process by process
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basis by the kernel. I'll call this the user segment.
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Anything above TASK_SIZE is common to all processes. I'll call
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this the kernel segment.
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(In other words, you can't put IO mappings below TASK_SIZE, and
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hence PAGE_OFFSET).
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TEXTADDR
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Virtual start address of kernel, normally PAGE_OFFSET + 0x8000.
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This is where the kernel image ends up. With the latest kernels,
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it must be located at 32768 bytes into a 128MB region. Previous
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kernels placed a restriction of 256MB here.
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DATAADDR
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Virtual address for the kernel data segment. Must not be defined
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when using the decompressor.
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VMALLOC_START / VMALLOC_END
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Virtual addresses bounding the vmalloc() area. There must not be
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any static mappings in this area; vmalloc will overwrite them.
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The addresses must also be in the kernel segment (see above).
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Normally, the vmalloc() area starts VMALLOC_OFFSET bytes above the
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last virtual RAM address (found using variable high_memory).
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VMALLOC_OFFSET
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Offset normally incorporated into VMALLOC_START to provide a hole
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between virtual RAM and the vmalloc area. We do this to allow
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out of bounds memory accesses (eg, something writing off the end
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of the mapped memory map) to be caught. Normally set to 8MB.
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Architecture Specific Macros
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----------------------------
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BOOT_MEM(pram,pio,vio)
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`pram` specifies the physical start address of RAM. Must always
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be present, and should be the same as PHYS_OFFSET.
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`pio` is the physical address of an 8MB region containing IO for
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use with the debugging macros in arch/arm/kernel/debug-armv.S.
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`vio` is the virtual address of the 8MB debugging region.
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It is expected that the debugging region will be re-initialised
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by the architecture specific code later in the code (via the
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MAPIO function).
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BOOT_PARAMS
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Same as, and see PARAMS_PHYS.
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FIXUP(func)
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Machine specific fixups, run before memory subsystems have been
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initialised.
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MAPIO(func)
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Machine specific function to map IO areas (including the debug
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region above).
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INITIRQ(func)
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Machine specific function to initialise interrupts.
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