arm64: Emulate SETEND for AArch32 tasks

Emulate deprecated 'setend' instruction for AArch32 bit tasks.

	setend [le/be] - Sets the endianness of EL0

On systems with CPUs which support mixed endian at EL0, the hardware
support for the instruction can be enabled by setting the SCTLR_EL1.SED
bit. Like the other emulated instructions it is controlled by an entry in
/proc/sys/abi/. For more information see :
	Documentation/arm64/legacy_instructions.txt

The instruction is emulated by setting/clearing the SPSR_EL1.E bit, which
will be reflected in the PSTATE.E in AArch32 context.

This patch also restores the native endianness for the execution of signal
handlers, since the process could have changed the endianness.

Note: All CPUs on the system must have mixed endian support at EL0. Once the
handler is registered, hotplugging a CPU which doesn't support mixed endian,
could lead to unexpected results/behavior in applications.

Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b1f9a20a3677..21a59bf37145 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -540,6 +540,21 @@ config CP15_BARRIER_EMULATION
 
           If unsure, say Y
 
+config SETEND_EMULATION
+        bool "Emulate SETEND instruction"
+        help
+          The SETEND instruction alters the data-endianness of the
+          AArch32 EL0, and is deprecated in ARMv8.
+
+          Say Y here to enable software emulation of the instruction
+          for AArch32 userspace code.
+
+          Note: All the cpus on the system must have mixed endian support at EL0
+          for this feature to be enabled. If a new CPU - which doesn't support mixed
+          endian - is hotplugged in after this feature has been enabled, there could
+          be unexpected results in the applications.
+
+          If unsure, say Y
 endif
 
 endmenu