How to map a data with openmp target to use inside a function?

Question

I would like to know how can I map a data for future use inside of a function?

I wrote some code like the following:

struct {
    int* a;
    int *b;
    // other members...
} s;

void func1(struct s* _s){
    int a* = _s->a;
    int b* = _s->b;
    // do something with _s

    #pragma omp target
    {
        // do something with a and b;
    }
}

int main(){
    struct s* _s;
    // alloc _s, a and b
    int *a = _s->a;
    int *b = _s->b;

    #pragma omp target data map(to: a, b)
    {
        func1(_s);
        // call another funcs with device use of mapped data...
    }

    // free data
}

The code compiles, but on execution Kernel execution error at <address> is spammed from verbose output of execution, followed by many Device kernel launch failed! and CUDA error is: an illegal memory access was encountered

Answer 1

Your map directive looks like it's probably mapping the value of the pointers a and b to the device rather than the arrays they're pointing to. I think you want to shape them so that the runtime maps the data and not just the pointers. Personally, I would also put the map clause on your target region too, since that gives the compiler more information to work with and the present check will find the data already on the device from the outer data region and not perform any further data movement.