Question

I am getting some warnings when compiling a custom Linux kernel. I have reduced my code (for debugging) to this:

int sw_totcp(struct ip_vs_service *svc)
{
        return(1);
}
EXPORT_SYMBOL(sw_totcp);

int (*sw_totcpcall)(struct ip_vs_service *) = &sw_totcp;
EXPORT_SYMBOL(sw_totcpcall);

And still getting these warnings (for both the function and the function pointer):

warning: data definition has no type or storage class [enabled by default]
warning: type defaults to ‘int’ in declaration of ‘EXPORT_SYMBOL’ [-Wimplicit-int]
warning: parameter names (without types) in function declaration [enabled by default]

They are properly declared in a header file like:

extern int sw_totcp(struct ip_vs_service *);

extern int (*sw_totcpcall)(struct ip_vs_service *);

What may be wrong?

Answer 1

It looks like you are not including the header where EXPORT_SYMBOL macro is defined. That is why the compiler is complaining about an implicit declaration: it thinks it’s a function returning an int.