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diff --git a/Documentation/powerpc/elfnote.rst b/Documentation/powerpc/elfnote.rst new file mode 100644 index 000000000000..06602248621c --- /dev/null +++ b/Documentation/powerpc/elfnote.rst @@ -0,0 +1,41 @@ +========================== +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 + |