1 ===================
2 Legacy instructions
3 ===================
4
5 The arm64 port of the Linux kernel provides in
6 emulation of instructions which have been depr
7 the architecture. The infrastructure code uses
8 hooks to support emulation. Where available it
9 the instruction execution in hardware.
10
11 The emulation mode can be controlled by writin
12 (/proc/sys/abi). The following explains the di
13 behaviours and the corresponding values of the
14
15 * Undef
16 Value: 0
17
18 Generates undefined instruction abort. Defau
19 have been obsoleted in the architecture, e.g
20
21 * Emulate
22 Value: 1
23
24 Uses software emulation. To aid migration of
25 usage of emulated instruction is traced as w
26 warnings are issued. This is the default for
27 instructions, .e.g., CP15 barriers
28
29 * Hardware Execution
30 Value: 2
31
32 Although marked as deprecated, some implemen
33 enabling/disabling of hardware support for t
34 instructions. Using hardware execution gener
35 performance, but at the loss of ability to g
36 about the use of the deprecated instructions
37
38 The default mode depends on the status of the
39 architecture. Deprecated instructions should d
40 while obsolete instructions must be undefined
41
42 Note: Instruction emulation may not be possibl
43 individual instruction notes for further infor
44
45 Supported legacy instructions
46 -----------------------------
47 * SWP{B}
48
49 :Node: /proc/sys/abi/swp
50 :Status: Obsolete
51 :Default: Undef (0)
52
53 * CP15 Barriers
54
55 :Node: /proc/sys/abi/cp15_barrier
56 :Status: Deprecated
57 :Default: Emulate (1)
58
59 * SETEND
60
61 :Node: /proc/sys/abi/setend
62 :Status: Deprecated
63 :Default: Emulate (1)*
64
65 Note: All the cpus on the system must have m
66 for this feature to be enabled. If a new CPU
67 endian - is hotplugged in after this feature
68 be unexpected results in the application.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.