Question

The following macro appears in include/linux/kernel.h

#define _THIS_IP_  ({ __label__ __here; __here: (unsigned long)&&__here; })

I don’t understand what the second & applied to __here would do. The first takes the address of the local label, but what about the second?

Answer 1

The second & in && is necessary to make GCC lookup the name as a label, instead of as a variable. For example

foo: ;
int foo;

void *p1 = &&foo;
void *p2 = &foo;

The second initializer refers to the int variable.