hwt_backend_read
.hwt_backend_read = pt_backend_read,
.hwt_backend_read = spe_backend_read,
error = ctx->hwt_backend->ops->hwt_backend_read(vm, ident,
int (*hwt_backend_read)(struct hwt_vm *, int *ident,
int hwt_backend_read(struct hwt_context *ctx, struct hwt_vm *vm, int *ident,
error = hwt_backend_read(ctx, vm, &ident, &offset, &data);