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author | Linus Torvalds | 2019-07-09 21:34:26 +0200 |
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committer | Linus Torvalds | 2019-07-09 21:34:26 +0200 |
commit | e9a83bd2322035ed9d7dcf35753d3f984d76c6a5 (patch) | |
tree | 66dc466ff9aec0f9bb7f39cba50a47eab6585559 /Documentation/arm64/legacy_instructions.rst | |
parent | Merge tag 'printk-for-5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/p... (diff) | |
parent | docs: automarkup.py: ignore exceptions when seeking for xrefs (diff) | |
download | kernel-qcow2-linux-e9a83bd2322035ed9d7dcf35753d3f984d76c6a5.tar.gz kernel-qcow2-linux-e9a83bd2322035ed9d7dcf35753d3f984d76c6a5.tar.xz kernel-qcow2-linux-e9a83bd2322035ed9d7dcf35753d3f984d76c6a5.zip |
Merge tag 'docs-5.3' of git://git.lwn.net/linux
Pull Documentation updates from Jonathan Corbet:
"It's been a relatively busy cycle for docs:
- A fair pile of RST conversions, many from Mauro. These create more
than the usual number of simple but annoying merge conflicts with
other trees, unfortunately. He has a lot more of these waiting on
the wings that, I think, will go to you directly later on.
- A new document on how to use merges and rebases in kernel repos,
and one on Spectre vulnerabilities.
- Various improvements to the build system, including automatic
markup of function() references because some people, for reasons I
will never understand, were of the opinion that
:c:func:``function()`` is unattractive and not fun to type.
- We now recommend using sphinx 1.7, but still support back to 1.4.
- Lots of smaller improvements, warning fixes, typo fixes, etc"
* tag 'docs-5.3' of git://git.lwn.net/linux: (129 commits)
docs: automarkup.py: ignore exceptions when seeking for xrefs
docs: Move binderfs to admin-guide
Disable Sphinx SmartyPants in HTML output
doc: RCU callback locks need only _bh, not necessarily _irq
docs: format kernel-parameters -- as code
Doc : doc-guide : Fix a typo
platform: x86: get rid of a non-existent document
Add the RCU docs to the core-api manual
Documentation: RCU: Add TOC tree hooks
Documentation: RCU: Rename txt files to rst
Documentation: RCU: Convert RCU UP systems to reST
Documentation: RCU: Convert RCU linked list to reST
Documentation: RCU: Convert RCU basic concepts to reST
docs: filesystems: Remove uneeded .rst extension on toctables
scripts/sphinx-pre-install: fix out-of-tree build
docs: zh_CN: submitting-drivers.rst: Remove a duplicated Documentation/
Documentation: PGP: update for newer HW devices
Documentation: Add section about CPU vulnerabilities for Spectre
Documentation: platform: Delete x86-laptop-drivers.txt
docs: Note that :c:func: should no longer be used
...
Diffstat (limited to 'Documentation/arm64/legacy_instructions.rst')
-rw-r--r-- | Documentation/arm64/legacy_instructions.rst | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/Documentation/arm64/legacy_instructions.rst b/Documentation/arm64/legacy_instructions.rst new file mode 100644 index 000000000000..54401b22cb8f --- /dev/null +++ b/Documentation/arm64/legacy_instructions.rst @@ -0,0 +1,68 @@ +=================== +Legacy instructions +=================== + +The arm64 port of the Linux kernel provides infrastructure to support +emulation of instructions which have been deprecated, or obsoleted in +the architecture. The infrastructure code uses undefined instruction +hooks to support emulation. Where available it also allows turning on +the instruction execution in hardware. + +The emulation mode can be controlled by writing to sysctl nodes +(/proc/sys/abi). The following explains the different execution +behaviours and the corresponding values of the sysctl nodes - + +* Undef + Value: 0 + + Generates undefined instruction abort. Default for instructions that + have been obsoleted in the architecture, e.g., SWP + +* Emulate + Value: 1 + + Uses software emulation. To aid migration of software, in this mode + usage of emulated instruction is traced as well as rate limited + warnings are issued. This is the default for deprecated + instructions, .e.g., CP15 barriers + +* Hardware Execution + Value: 2 + + Although marked as deprecated, some implementations may support the + enabling/disabling of hardware support for the execution of these + instructions. Using hardware execution generally provides better + performance, but at the loss of ability to gather runtime statistics + about the use of the deprecated instructions. + +The default mode depends on the status of the instruction in the +architecture. Deprecated instructions should default to emulation +while obsolete instructions must be undefined by default. + +Note: Instruction emulation may not be possible in all cases. See +individual instruction notes for further information. + +Supported legacy instructions +----------------------------- +* SWP{B} + +:Node: /proc/sys/abi/swp +:Status: Obsolete +:Default: Undef (0) + +* CP15 Barriers + +:Node: /proc/sys/abi/cp15_barrier +:Status: Deprecated +:Default: Emulate (1) + +* SETEND + +:Node: /proc/sys/abi/setend +:Status: Deprecated +:Default: Emulate (1)* + + Note: All the cpus on the system must have mixed endian support at EL0 + for this feature to be enabled. If a new CPU - which doesn't support mixed + endian - is hotplugged in after this feature has been enabled, there could + be unexpected results in the application. |