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From: Peter Maydell <peter.maydell@linaro.org>
Date: Tue, 23 Jun 2015 09:04:11 +0100
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Subject: Re: [Qemu-devel] [PATCH v3 04/11] linux-user: arm: set CPSR.E
 correctly for BE8 mode
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To: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>

On 22 June 2015 at 23:48, Peter Crosthwaite
<peter.crosthwaite@xilinx.com> wrote:
> On Thu, Jun 26, 2014 at 7:18 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 26/06/2014 16:15, Peter Maydell ha scritto:
>>>
>>> (There is code for handling CPSR_E in the kernel's start_thread()
>>> macro but that is actually only called for starting new
>>> processes, AFAICT.)
>>
>>
>> Yes, you're right.
>>
>
> So I am struggling on figuring out the need to have this extra state
> of signal_cpsr_e. Is it still needed and to follow up, would something
> similar be needed for SCTLR.E0E on AA64 support?

The Linux userland ABI says:
 (1) the ELF file defines whether an executable is BE8 or not
 (2) this setting affects:
    (a) whether we start at the process entry point in BE or LE
    (b) whether we run signal handlers in BE or LE
    (c) whether newly cloned threads start in BE or LE

signal_cpsr_e is how this patch implements that -- we set it
based on the ELF file flags, then set CPSR.E based on it:
 * in main, for the initial thread
 * in cpu_clone_regs, for subsequent threads
 * in signal.c, for signal handlers

For AArch64 BE we will need something similar. I don't know if
there's somewhere more appropriate to store this "what's the
ELF file endianness" state, but we do need to keep it somewhere...

thanks
-- PMM