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