On 12/6/19 9:24 AM, Peter Maydell wrote:
>> + union {
>> + /*
>> + * Offsets of the secure and non-secure fields in CPUARMState for
>> + * the register if it is banked. These fields are only used during
>> + * the static registration of a register. During hashing the bank
>> + * associated with a given security state is copied to fieldoffset
>> + * which is used from there on out.
>> + *
>> + * It is expected that register definitions use either fieldoffset
>> + * or bank_fieldoffsets in the definition but not both. It is also
>> + * expected that both bank offsets are set when defining a banked
>> + * register. This use indicates that a register is banked.
>> + */
>> + ptrdiff_t bank_fieldoffsets[2];
>> +
>> + /*
>> + * "Original" writefn and readfn.
>> + * For ARMv8.1-VHE register aliases, we overwrite the read/write
>> + * accessor functions of various EL1/EL0 to perform the runtime
>> + * check for which sysreg should actually be modified, and then
>> + * forwards the operation. Before overwriting the accessors,
>> + * the original function is copied here, so that accesses that
>> + * really do go to the EL1/EL0 version proceed normally.
>> + * (The corresponding EL2 register is linked via opaque.)
>> + */
>> + struct {
>> + CPReadFn *orig_readfn;
>> + CPWriteFn *orig_writefn;
>> + };
>
> Does this really need to be a union ? It's not clear to me
> why we know the two halves of it are never used at the same time.
We don't really need to use a union. I should probably change that. I think
AJB had the same question vs one of the previous revisions.
We know they're not used at the same time because bank_fieldoffsets is only
used *before* the structure is duplicated and added into the hash table
(overwriting .fieldoffset depending on the bank as they are duplicated), and
orig_{read,write}fn are only used *after* the structure has been added to the
hash table.
>> +static void el2_e2h_write(CPUARMState *env, const ARMCPRegInfo *ri,
>> + uint64_t value)
>> +{
>> + CPWriteFn *writefn;
>> +
>> + if (redirect_for_e2h(env)) {
>> + /* Switch to the saved EL2 version of the register. */
>> + ri = ri->opaque;
>> + writefn = ri->writefn;
>> + } else {
>> + writefn = ri->orig_writefn;
>> + }
>> + if (writefn == NULL) {
>> + writefn = raw_write;
>> + }
>> + writefn(env, ri, value);
>> +}
>
> I see how this works when we have a readfn or writefn,
> but how does the redirection work where the access
> goes directly via .fieldoffset ?
When there is no .writefn, we use raw_write, which uses fieldoffset.
r~
