| 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. |
