1 Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE)
2 ---------------------------------------------------------------------
3
4 ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommends
5 moving to the load-locked/store-conditional instructions LDREX and STREX.
6
7 ARMv7 multiprocessing extensions introduce the ability to disable these
8 instructions, triggering an undefined instruction exception when executed.
9 Trapped instructions are emulated using an LDREX/STREX or LDREXB/STREXB
10 sequence. If a memory access fault (an abort) occurs, a segmentation fault is
11 signalled to the triggering process.
12
13 /proc/cpu/swp_emulation holds some statistics/information, including the PID of
14 the last process to trigger the emulation to be invocated. For example::
15
16 Emulated SWP: 12
17 Emulated SWPB: 0
18 Aborted SWP{B}: 1
19 Last process: 314
20
21
22 NOTE:
23 when accessing uncached shared regions, LDREX/STREX rely on an external
24 transaction monitoring block called a global monitor to maintain update
25 atomicity. If your system does not implement a global monitor, this option can
26 cause programs that perform SWP operations to uncached memory to deadlock, as
27 the STREX operation will always fail.
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