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- Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE)
- ---------------------------------------------------------------------
- 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.
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