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CONFIG_SWP_EMULATE: Emulate SWP/SWPB instructions

General informations

The Linux kernel configuration item CONFIG_SWP_EMULATE:

Help text

ARMv6 architecture deprecates use of the SWP/SWPB instructions. ARMv7 multiprocessing extensions introduce the ability to disable these instructions, triggering an undefined instruction exception when executed. Say Y here to enable software emulation of these instructions for userspace (not kernel) using LDREX/STREX. Also creates /proc/cpu/swp_emulation for statistics.

In some older versions of glibc [<=2.8] SWP is used during futex trylock() operations with the assumption that the code will not be preempted. This invalid assumption may be more likely to fail with SWP emulation enabled, leading to deadlock of the user application.

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.

If unsure, say Y.

Hardware

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