Documentation/arch/arm/porting.rst

File Facts

System

Linux kernel

Corpus path

Documentation/arch/arm/porting.rst

Extension

.rst

Size

4514 bytes

Lines

138

Domain

Support Tooling And Documentation

Bucket

Documentation

Inferred role

Support Tooling And Documentation: documentation

Status

atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

• Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
• Allocates kernel memory; connect allocation flags and lifetime to context constraints.
• Defines or uses C structs; map object ownership, embedded links, reference counts, and lock ownership.

Dependency Surface

• No C-style include directives detected by the generator.

Detected Declarations

• No top-level syscall, struct, function, initcall, or export declaration detected by the generator.

Annotated Snippet

=======
Porting
=======

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

Annotation

• Atlas domain: Support Tooling And Documentation / Documentation.
• Implementation status: atlas-only.

Implementation Notes

• This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
• Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
• Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.