Re: [Qemu-devel] [PATCH v3 04/11] linux-user: arm: set CPSR.E correctly for BE8 mode

[Peter Maydell <peter.maydell@linaro.org>]

On 24 June 2015 at 11:09, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>
> On 23/06/2015 22:30, Peter Crosthwaite wrote:
>> > I'm confused. arm_cpu_is_big_endian() tells you whether the CPU
>> > is *currently* big-endian or not. That doesn't help you with
>> > answering the question "I'm about to run a signal handler; what
>> > should I set the CPSR.E bit to?" in linux-user mode. That's
>> > what signal_cpsr_e does.
>>
>> arm_cpu_is_bigendian is the consumer of this information. We still
>> need some state for signal_cpsr_e, just the question is what state
>> does that set. If we reuse arm_cpu_is_big_endian, then signal_cpsr_e
>> (or its rename) needs to drive CPSR.E as well as SCTLR.E0E.
>
> I think signal_cpsr_e is exactly what you want for AArch32.  It sets
> CPSR.E in main and setup_return for AArch32.
>
> For AArch64 you don't need anything because, even though the kernel does
> trap setend and tweak SCTLR.E0E in response to it, setup_return doesn't
> try to restore the native endianness.

I didn't think SETEND existed at all in AArch64? It's a 32-bit only
instruction. So the AArch64 setup is anyway much simpler because
you don't have to worry about the userspace code being a different
endianness to what you want to run the signal handler as.

-- PMM