Re: [PATCH v5 1/5] hyperv: Define struct hv_output_get_vp_registers

[Roman Kisel]

On 1/6/2025 9:37 AM, Michael Kelley wrote:
> From: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx> Sent: Monday, December 30, 2024 10:10 AM
[...]
> These bit field definitions don't look right. We want to "fill up"
> the field size, so that we're explicit about each bit, and not leave
> it to the compiler to add padding (which __packed tells the
> compiler not to do). So in aggregate, the "u64" bit fields should
> account for all 64 bits, but here you account for only 32 bits.
> There are two ways to fix this:
>
> 		u32 interruption_pending : 1;
> 		u32 interruption_type: 1;
> 		u32 reserved : 30;
> 		u32 error_code;
> Or
> 		u64 interruption_pending : 1;
> 		u64 interruption_type: 1;
> 		u64 reserved : 30;
> 		u64 error_code : 32;
>
>
> Nuno -- your thoughts?

Quite a blunder on my side! Thank you very much for your help :)
GDB is my witness:

(gdb) ptype /o union hv_arm64_pending_synthetic_exception_event
/* offset      |    size */  type = union 
hv_arm64_pending_synthetic_exception_event {
/*                    16 */    u64 as_uint64[2];
/*                    13 */    struct {
/*      0: 0   |       4 */        u32 event_pending : 1;
/*      0: 1   |       4 */        u32 event_type : 3;
/*      0: 4   |       4 */        u32 reserved : 4;
/*      1      |       4 */        u32 exception_type;
/*      5      |       8 */        u64 context;

                                   /* total size (bytes):   13 */
                               };

                               /* total size (bytes):   16 */
                             }

which looks messed up to me to put it mildly. Will fix next time.

[...]

> Michael
>
> > +
> > +/*
> > + * NOTE: Linux helper struct - NOT from Hyper-V code.
> > + * DECLARE_FLEX_ARRAY() needs to be wrapped into
> > + * a structure and have at least one more member besides
> > + * DECLARE_FLEX_ARRAY.
> > + */
> > +struct hv_output_get_vp_registers {
> > +	struct {
> > +		DECLARE_FLEX_ARRAY(union hv_register_value, values);
> > +		struct {} values_end;
> > +	};
> >   };
> >
> >   #if defined(CONFIG_ARM64)
> > --
> > 2.34.1

--
Thank you,
Roman