Is this a BUG GCC/CLANG?

Is this a BUG? GCC 7/8/9 - compile OK. CLANG 9.0.1 - compile OK.

http://tpcg.io/InKuRSMh

typedef struct key_val_t{
    char key[255];
    char val[255];
} key_val_t;
int compare_str(const void* data1, const void* data2)
{
    if(!data1 || !data2)
    return -2;
    const void* val1 = ((key_val_t*) val1)->key;   // <------ What's is val1?
    const void* val2 = data2;
    return strncmp(val1, val2, strlen(val2));
}