The following commands show a contrived single file program, build it, then create the call graph XML file.

% type file.c
volatile double v1, v2;

int main()
{
    return v1 * v2 != 1.0;
}

% c29clang file.c -o file.out -Wl,-c,-m=file.map

% c29ofd --call_graph file.out > graph.xml

Inspect the call graph in graph.xml. There is no entry for the function main. main is called from the function c_int00_noargs. The function c_int00_noargs appears, and is shown to call yet other functions. But not main. It is likely there are yet other problems similar in nature.