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authorPunit Agrawal <punit.agrawal@arm.com>2014-11-18 11:41:25 +0000
committerWill Deacon <will.deacon@arm.com>2014-11-20 16:34:31 +0000
commitbd35a4adc4131c530ec7d90242555eac7b3dbe3f (patch)
tree61db668ee8924e5dae4aa53fadf8b8ffde6bba3b /arch/arm64/Kconfig
parent587064b610c703f259317d00dc37bf6d40f4fc74 (diff)
downloadlinux-bd35a4adc4131c530ec7d90242555eac7b3dbe3f.tar.bz2
arm64: Port SWP/SWPB emulation support from arm
The SWP instruction was deprecated in the ARMv6 architecture. The ARMv7 multiprocessing extensions mandate that SWP/SWPB instructions are treated as undefined from reset, with the ability to enable them through the System Control Register SW bit. With ARMv8, the option to enable these instructions through System Control Register was dropped as well. To support legacy applications using these instructions, port the emulation of the SWP and SWPB instructions from the arm port to arm64. Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Punit Agrawal <punit.agrawal@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/Kconfig')
-rw-r--r--arch/arm64/Kconfig21
1 files changed, 21 insertions, 0 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index aa8f4bea3738..2b6213840ec8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -180,6 +180,27 @@ menuconfig ARMV8_DEPRECATED
if ARMV8_DEPRECATED
+config SWP_EMULATION
+ bool "Emulate SWP/SWPB instructions"
+ help
+ 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.
+
+ 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
+
endif
endmenu