The future GCC 6 is making heavier use of DW_AT_specification, which cgo does not understand. This was reported against gccgo as https://gcc.gnu.org/PR68072, but it is a general Go problem. Filing this here to consider adding the patch (which I will send out momentarily) to Go 1.5.2.

The bug can occur in various ways, but the simplest is when there is both an external declaration for a variable and a real declaration, as in

// extern int i;
// int i;
import "C"

Of course in practice the extern int i; would be in a header file. GCC 6 now generates a DW_AT_specification pointing from one declaration to the other. (This is part of the early debug work described at https://gcc.gnu.org/wiki/early-debug .) The cgo tool sees a variable entry that uses DW_AT_specification, an entry that has no name or type, and issues a "malformed DWARF TagVariable entry" error.