Re: [Xen-devel] [PATCH v4 5/8] arm/vm_event: get/set registers

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Mon, May 30, 2016 at 5:50 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> On 30.05.16 at 00:37, <tamas@xxxxxxxxxxxxx> wrote:
>> +struct vm_event_regs_arm32 {
>> +    uint32_t r0_usr;
>> +    uint32_t r1_usr;
>> +    uint32_t r2_usr;
>> +    uint32_t r3_usr;
>> +    uint32_t r4_usr;
>> +    uint32_t r5_usr;
>> +    uint32_t r6_usr;
>> +    uint32_t r7_usr;
>> +    uint32_t r8_usr;
>> +    uint32_t r9_usr;
>> +    uint32_t r10_usr;
>> +    uint32_t r12_usr;
>> +    uint32_t lr_usr;
>> +    uint32_t fp;
>> +    uint32_t pc;
>> +    uint32_t sp_usr;
>> +    uint32_t sp_svc;
>> +    uint32_t spsr_svc;
>> +};
>
> It would seem more natural for the "ordinary" registers to be
> arranged in the numerical sequence, i.e. fp, r12, sp, lr, pc.

Not sure I follow.

>
>> +struct vm_event_regs_arm64 {
>> +    uint64_t x0;
>> +    uint64_t x1;
>> +    uint64_t x2;
>> +    uint64_t x3;
>> +    uint64_t x4;
>> +    uint64_t x5;
>> +    uint64_t x6;
>> +    uint64_t x7;
>> +    uint64_t x8;
>> +    uint64_t x9;
>> +    uint64_t x10;
>> +    uint64_t x16;
>> +    uint64_t lr;
>> +    uint64_t fp;
>> +    uint64_t pc;
>> +    uint64_t sp_el0;
>> +    uint64_t sp_el1;
>> +    uint32_t spsr_el1;
>> +    uint32_t _pad;
>> +};
>
> My ARM knowledge is certainly quite limited, but the incomplete set
> of GPRs here is quite obvious: Is there a reason to not make all of
> them available here? And if there is, could the criteria of which
> registers got put here please be documented in a comment (so that
> the next person noticing the incomplete set won't ask again)?

There already is a comment in place that explains why we are not
sending the full set of registers here.

>
> I'm also puzzled by fp and lr - I'm not aware of registers of those
> names (and gas also doesn't accept them afaict).

Not sure why but Xen names x29 fp and x30 lr. See
include/asm-arm/arm64/processor.h.

>
>> +struct vm_event_regs_arm {
>> +    uint32_t cpsr; /* PSR_MODE_BIT is set iff arm32 is used below */
>
> Explicit padding missing after this one.

Ack.

Thanks,
Tamas

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