Re: [Qemu-devel] ARM invalid co-processor register

[Peter Maydell]

On 25 May 2016 at 06:44, Karthik <address@hidden> wrote:
> Hi,
>
> CPU: Cortex R5F
>
> I have this instruction that invalidates the entire data cache
>
> MCR p15, 0, r0, c15, c5, 0
>
>
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0460c/Chdhgibd.html
>
> This instruction generates undefined exception, and further debugging
> showed it is because the co-processor register was not implemented.
>
> To get around, I have added the below entry in the cortexr5_cp_reginfo[]
> (target-arm/cpu.c)
>
> {
>     {.name = "INVALLDC", .cp=15, .opc1 = 0, .crn = 5, .opc2 = 0.
>      .access = PL1_W, .type = ARM_CP_NOP | ARM_CP_OVERRIDE},
> }
>
> or
>
> I have to add
> set_feature(&cpu->env, ARM_FEATURE_DUMMY_C15_REGS);
>
> So, which option is recommended?

Better to implement exactly the registers that are required;
the DUMMY_C15_REGS feature is mostly there for our older CPU
emulation because it's what we've always done, and it's a bit
tricky to move to being more specific without potentially breaking
guest code that used to work. We shouldn't be adding it to more
CPUs.

You should check against the ARM ARM whether these cache
invalidation registers are really R5-specific, or if they're
a part of the generic PMSA architecture. If they're generic
PMSA then they should be implemented in the generic code,
enabled by a new feature flag, not in the R5-only reginfo
array.

thanks
-- PMM