diff options
| author | Alex Van Brunt <avanbrunt@nvidia.com> | 2014-01-30 15:10:39 -0800 |
|---|---|---|
| committer | Alexander Van Brunt <avanbrunt@nvidia.com> | 2014-02-15 07:45:08 -0800 |
| commit | 78faf3dda07b85a821c9f118c595574d8e71d356 (patch) | |
| tree | 7205775afd10a16e884e7e19e1d1369ecd3a862a /arch/arm64/Kconfig | |
| parent | 679b362a6fc9c5eb944042ddc700a0d093a12342 (diff) | |
arm64: emulate the swp/swpb instruction
The swp and spwb instructions were deprecated in ARMv6. ARMv8
obsoleted the instruction. Despite this, many applications rely on
these instruuctions.
This patch starts with the version present in the arm architecture.
However, it uses the ldx*()/stx*() functions to implement the handler
in C code. It also removes a lot of code that is not needed.
Bug 1438816
Change-Id: I6882fbe5f71bfa8f9e9a75d067b2111188c6f2fa
Signed-off-by: Alex Van Brunt <avanbrunt@nvidia.com>
Reviewed-on: http://git-master/r/366097
Reviewed-by: Richard Wiley <rwiley@nvidia.com>
Tested-by: Oskari Jaaskelainen <oskarij@nvidia.com>
Diffstat (limited to 'arch/arm64/Kconfig')
| -rw-r--r-- | arch/arm64/Kconfig | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index aeecfdac027b..d680ed628c2f 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -205,6 +205,31 @@ config HOTPLUG_CPU If you don't know what to do here, say N. +config SWP_EMULATE + bool "Emulate SWP/SWPB instructions" + help + ARMv6 architecture deprecates use of the SWP/SWPB instructions. ARMv8 + oblosetes the use of 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. + source kernel/Kconfig.preempt config ARCH_NR_GPIO @@ -247,6 +272,7 @@ config HW_PERF_EVENTS config ARMV7_COMPAT bool "Kernel support for ARMv7 applications" depends on COMPAT + select SWP_EMULATE help This option enables features that allow that ran on an ARMv7 or older processor to continue functioning. |