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authorMaxiwell S. Garcia <maxiwell@linux.ibm.com>2019-08-29 12:50:21 -0300
committerMichael Ellerman <mpe@ellerman.id.au>2019-08-30 09:40:15 +1000
commit134cb3ab71c0736da0ec66d2cfd7f6ebba96c8cf (patch)
treec4528f487f5bb55a6f1b0887508db5ffcde2e4eb /Documentation/powerpc
parent70ed86f4de5bd74dd2d884dcd2f3275c4cfe665f (diff)
Documentation/powerpc: Add ELF note documentation
The ELF note documentation describes the types and descriptors to be used with the PowerPC namespace. Signed-off-by: Maxiwell S. Garcia <maxiwell@linux.ibm.com> Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20190829155021.2915-3-maxiwell@linux.ibm.com
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+==========================
+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 the
+include/uapi/asm/elfnote.h
+
+ 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).
+
+ #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
+----------
+
+arch/powerpc/include/asm/elfnote.h
+arch/powerpc/kernel/note.S
+
+