I pass a struct pointer to a device function, and this device function edits this pointer.

struct:

struct substruct{
    int main;
    int sub;
};

struct mainstruct{
    int main;
    int sub;
    substruct* subs;
};

device function:

__global__ void update(mainstruct* target){
    printf("in device: target: %d/%d/%dn", target->main, target->sub, target->subs);
    //substruct *sub = new substruct();
    substruct* sub;
    cudaMalloc(&sub, sizeof(substruct));
    sub->main = 5;
    sub->sub = 5;
    target->subs = sub;
    printf("in device: sub created/allocated: %d/%dn", sub->main, sub->sub);
}

and this is main:

int main(){
    mainstruct *main = new mainstruct();
    main->main = 10;
    main->sub = 10;
    main->subs = nullptr;

    mainstruct* main_device;
    handleerr(cudaMalloc(&main_device, sizeof(mainstruct)));
    handleerr(cudaMemcpy(main_device, main, sizeof(mainstruct), cudaMemcpyHostToDevice));
    
    update << <1, 1 >> > (main_device);
    handleerr(cudaDeviceSynchronize());
    handleerr(cudaGetLastError());

    handleerr(cudaMemcpy(main, main_device, sizeof(mainstruct), cudaMemcpyDeviceToHost));
    substruct *subs = new substruct();
    handleerr(cudaMallocHost(&subs, sizeof(substruct)));
    handleerr(cudaMemcpy(subs, main->subs, sizeof(substruct), cudaMemcpyDeviceToHost));

    main->subs = subs;

    printf("done");
}

I keep encountering an error at the line :
handleerr(cudaMemcpy(subs, main->subs, sizeof(substruct), cudaMemcpyDeviceToHost));

how can I correctly copy memory that was dynamically allocated??