1Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE) 2--------------------------------------------------------------------- 3 4ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommends 5moving to the load-locked/store-conditional instructions LDREX and STREX. 6 7ARMv7 multiprocessing extensions introduce the ability to disable these 8instructions, triggering an undefined instruction exception when executed. 9Trapped instructions are emulated using an LDREX/STREX or LDREXB/STREXB 10sequence. If a memory access fault (an abort) occurs, a segmentation fault is 11signalled to the triggering process. 12 13/proc/cpu/swp_emulation holds some statistics/information, including the PID of 14the 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 22NOTE: 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. 28