[linux-2.6-block.git] / Documentation / powerpc / elfnote.rst

==========================
ELF Note PowerPC Namespace
==========================

The PowerPC namespace in an ELF Note of the kernel binary is used to store
capabilities and information which can be used by a bootloader or userland.

Types and Descriptors
---------------------

The types to be used with the "PowerPC" namesapce are defined in [#f1]_.

	1) PPC_ELFNOTE_CAPABILITIES

Define the capabilities supported/required by the kernel. This type uses a
bitmap as "descriptor" field. Each bit is described below:

- Ultravisor-capable bit (PowerNV only).

.. code-block:: c

	#define PPCCAP_ULTRAVISOR_BIT (1 << 0)

Indicate that the powerpc kernel binary knows how to run in an
ultravisor-enabled system.

In an ultravisor-enabled system, some machine resources are now controlled
by the ultravisor. If the kernel is not ultravisor-capable, but it ends up
being run on a machine with ultravisor, the kernel will probably crash
trying to access ultravisor resources. For instance, it may crash in early
boot trying to set the partition table entry 0.

In an ultravisor-enabled system, a bootloader could warn the user or prevent
the kernel from being run if the PowerPC ultravisor capability doesn't exist
or the Ultravisor-capable bit is not set.

References
----------

.. [#f1] arch/powerpc/include/asm/elfnote.h
Commit	Line	Data
134cb3ab MG	1	==========================
	2	ELF Note PowerPC Namespace
	3	==========================
	4
	5	The PowerPC namespace in an ELF Note of the kernel binary is used to store
	6	capabilities and information which can be used by a bootloader or userland.
	7
	8	Types and Descriptors
	9	---------------------
	10
ad9b48c5	11	The types to be used with the "PowerPC" namesapce are defined in [#f1]_.
134cb3ab MG	12
	13	1) PPC_ELFNOTE_CAPABILITIES
	14
	15	Define the capabilities supported/required by the kernel. This type uses a
	16	bitmap as "descriptor" field. Each bit is described below:
	17
	18	- Ultravisor-capable bit (PowerNV only).
	19
ad9b48c5 AZ	20	.. code-block:: c
ad9b48c5 AZ	21
134cb3ab MG	22	#define PPCCAP_ULTRAVISOR_BIT (1 << 0)
134cb3ab MG	23
ad9b48c5 AZ	24	Indicate that the powerpc kernel binary knows how to run in an
ad9b48c5 AZ	25	ultravisor-enabled system.
134cb3ab	26
ad9b48c5 AZ	27	In an ultravisor-enabled system, some machine resources are now controlled
	28	by the ultravisor. If the kernel is not ultravisor-capable, but it ends up
	29	being run on a machine with ultravisor, the kernel will probably crash
	30	trying to access ultravisor resources. For instance, it may crash in early
	31	boot trying to set the partition table entry 0.
134cb3ab	32
ad9b48c5 AZ	33	In an ultravisor-enabled system, a bootloader could warn the user or prevent
	34	the kernel from being run if the PowerPC ultravisor capability doesn't exist
	35	or the Ultravisor-capable bit is not set.
134cb3ab MG	36
	37	References
	38	----------
	39
ad9b48c5	40	.. [#f1] arch/powerpc/include/asm/elfnote.h
134cb3ab	41