Based on kernel version 4.16.1. Page generated on 2018-04-09 11:52 EST.
1 The arm64 port of the Linux kernel provides infrastructure to support 2 emulation of instructions which have been deprecated, or obsoleted in 3 the architecture. The infrastructure code uses undefined instruction 4 hooks to support emulation. Where available it also allows turning on 5 the instruction execution in hardware. 6 7 The emulation mode can be controlled by writing to sysctl nodes 8 (/proc/sys/abi). The following explains the different execution 9 behaviours and the corresponding values of the sysctl nodes - 10 11 * Undef 12 Value: 0 13 Generates undefined instruction abort. Default for instructions that 14 have been obsoleted in the architecture, e.g., SWP 15 16 * Emulate 17 Value: 1 18 Uses software emulation. To aid migration of software, in this mode 19 usage of emulated instruction is traced as well as rate limited 20 warnings are issued. This is the default for deprecated 21 instructions, .e.g., CP15 barriers 22 23 * Hardware Execution 24 Value: 2 25 Although marked as deprecated, some implementations may support the 26 enabling/disabling of hardware support for the execution of these 27 instructions. Using hardware execution generally provides better 28 performance, but at the loss of ability to gather runtime statistics 29 about the use of the deprecated instructions. 30 31 The default mode depends on the status of the instruction in the 32 architecture. Deprecated instructions should default to emulation 33 while obsolete instructions must be undefined by default. 34 35 Note: Instruction emulation may not be possible in all cases. See 36 individual instruction notes for further information. 37 38 Supported legacy instructions 39 ----------------------------- 40 * SWP{B} 41 Node: /proc/sys/abi/swp 42 Status: Obsolete 43 Default: Undef (0) 44 45 * CP15 Barriers 46 Node: /proc/sys/abi/cp15_barrier 47 Status: Deprecated 48 Default: Emulate (1) 49 50 * SETEND 51 Node: /proc/sys/abi/setend 52 Status: Deprecated 53 Default: Emulate (1)* 54 Note: All the cpus on the system must have mixed endian support at EL0 55 for this feature to be enabled. If a new CPU - which doesn't support mixed 56 endian - is hotplugged in after this feature has been enabled, there could 57 be unexpected results in the application.