Re: [PATCH 3/3] arm64: Emulate SETEND for AArch32 tasks

Mark Rutland
2015-01-16T16:56:25Z

On Thu, Jan 15, 2015 at 12:36:06PM +0000, Suzuki K. Poulose wrote:
> From: "Suzuki K. Poulose" <suzuki.poulose@arm.com>
>
> 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 should support for mixed endian at EL0. Once the
> handler is registered a CPU which doesn't support mixed endian, cannot be
> hotplugged in.
>
> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
> ---
> Documentation/arm64/legacy_instructions.txt | 9 +++
> arch/arm64/Kconfig | 10 ++++
> arch/arm64/include/asm/cpufeature.h | 1 +
> arch/arm64/include/asm/ptrace.h | 7 +++
> arch/arm64/kernel/armv8_deprecated.c | 82 +++++++++++++++++++++++++++
> arch/arm64/kernel/signal32.c | 5 +-
> 6 files changed, 113 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/arm64/legacy_instructions.txt b/Documentation/arm64/legacy_instructions.txt
> index 0a4dc26..92b7945 100644
> --- a/Documentation/arm64/legacy_instructions.txt
> +++ b/Documentation/arm64/legacy_instructions.txt
> @@ -47,3 +47,12 @@ Default: Undef (0)
> Node: /proc/sys/abi/cp15_barrier
> Status: Deprecated
> Default: Emulate (1)
> +
> +* SETEND
> +Node: /proc/sys/abi/setend
> +Status: Deprecated
> +Default: Emulate (1)*
> +Note: All the cpus on the system should support mixed endian at EL0
> +(ID_AA64MMFR0_EL1:BigEnd or BigEndEL0), for this feature to be enabled.

This might read a little better as:

Note: all CPUs in the system must have mixed-endian support at EL0 for
this feature to be enabled.

That matches the ARM ARM wording for ID_AA64MMFR0_EL1. We shouldn't need
to mention the particular register fields here.

Also, we should probably add a note at the top like:

Note: instruction emulation may not be possible in all cases. See
below for further information.

Thanks,
Mark.