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Diffstat (limited to 'Documentation/arm64/legacy_instructions.txt')
-rw-r--r-- | Documentation/arm64/legacy_instructions.txt | 57 |
1 files changed, 0 insertions, 57 deletions
diff --git a/Documentation/arm64/legacy_instructions.txt b/Documentation/arm64/legacy_instructions.txt deleted file mode 100644 index 01bf3d9fac85..000000000000 --- a/Documentation/arm64/legacy_instructions.txt +++ /dev/null @@ -1,57 +0,0 @@ -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 - -Supported legacy instructions ------------------------------ -* SWP{B} -Node: /proc/sys/abi/swp -Status: Obsolete -Default: Undef (0) - -* CP15 Barriers -Node: /proc/sys/abi/cp15_barrier -Status: Deprecated -Default: Emulate (1) - -* SETEND -Node: /proc/sys/abi/setend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. |