CONFIG_SWP_EMULATION: Emulate SWP/SWPB instructions

General informations

The Linux kernel configuration item CONFIG_SWP_EMULATION:

• prompt: Emulate SWP/SWPB instructions
• type: bool
• depends on: (none)
• defined in arch/arm64/Kconfig
• found in Linux kernels: 3.19, 4.0–4.20, 5.0–5.19, 6.0–6.8, 6.9-rc+HEAD

Help text

ARMv8 obsoletes the use of A32 SWP/SWPB instructions such that they are always undefined. Say Y here to enable software emulation of these instructions for userspace using LDXR/STXR. This feature can be controlled at runtime with the abi.swp sysctl which is disabled by default.

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, LDXR/STXR 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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This page is automaticly generated with free (libre, open) software lkddb(see lkddb-sources).

The data is retrived from:

• Linux kernel
• Linux Kernel Driver DataBase (LKDDb)

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