Re: [Qemu-devel] [PATCH 10/15] target/arm: Don't use cpsr_write/cpsr_read to transfer M profile XPSR

[Peter Maydell]

On 3 August 2017 at 23:13, Richard Henderson <address@hidden> wrote:
> On 08/02/2017 09:43 AM, Peter Maydell wrote:
>> +        if (val & XPSR_EXCP) {
>> +            /* This is a CPSR format value from an older QEMU. (We can tell
>> +             * because values transferred in XPSR format always have zero
>> +             * for the EXCP field, and CPSR format will always have bit 4
>> +             * set in CPSR_M.) Rearrange it into XPSR format. The 
>> significant
>> +             * differences are that the T bit is not in the same place, the
>> +             * primask/faultmask info may be in the CPSR I and F bits, and
>> +             * we do not want the mode bits.
>> +             */
>> +            uint32_t newval = val;
>> +
>> +            newval &= (CPSR_NZCV | CPSR_Q | CPSR_IT | CPSR_GE);
>> +            if (val & CPSR_T) {
>> +                newval |= XPSR_T;
>> +            }
>> +            /* If the I or F bits are set then this is a migration from
>> +             * an old QEMU which still stored the M profile FAULTMASK
>> +             * and PRIMASK in env->daif. For a new QEMU, the data is
>> +             * transferred using the vmstate_m_faultmask_primask subsection.
>> +             */
>
> The second comment seems sort of redundant with the first now.

I felt that the migration-compat stuff was sufficiently subtle
that it was worth retaining the second detailed comment as well
as the brief summary in the new first comment.

thanks
-- PMM