Gccgo error passing and modifying C struct in go - c

Question

I'm attempting to convert a go library to be called by C and I'm starting with a simple test (based on an example answering another question I found that worked) file but I'm getting errors when I try to build. I have a struct in C that I'm trying to pass to a go function which uses data from that struct and returns a value (in this case an integer, but eventually it would be another struct).
Go version: 1.4.2
gccgo version: 5.0.1
gcc version: 4.9.2
type.h
typedef struct num {
int n;
} num;
foo.go
package main
// #include "type.h"
import "C"
func New(x int) C.struct_num {
num := C.struct_num{}
num.n = C.int(x)
return num
}
func Add(num C.struct_num, x int) int {
return int(num.n) + x
}
bar.c
#include <stdio.h>
#include "type.h"
extern num go_new(int) __asm__ ("example.main.New");
extern int go_add(num, int) __asm__ ("example.main.Add");
int main() {
num n = go_new(2);
int x = go_add(n, 3);
printf("Result: %d\n", x);
}
Makefile
all: main
main: foo.o bar.c
gcc foo.o bar.c -o main
foo.o: foo.go
go build -compiler gccgo -gccgoflags '-c -o foo.o -fgo-prefix=example' foo.go
clean:
rm -f main *.o
When I run make I get the error:
gcc foo.o bar.c -o main
foo.o:(.rodata.__go_td_pN23_example.main._Ctype_int[__go_td_pN23_example.main._Ctype_int]+0x18): undefined reference to `__go_type_hash_identity'
foo.o:(.rodata.__go_td_pN23_example.main._Ctype_int[__go_td_pN23_example.main._Ctype_int]+0x20): undefined reference to `__go_type_equal_identity'
foo.o:(.rodata.__go_tdn_example.main..example_main._Ctype_int+0x18): undefined reference to `__go_type_hash_identity'
foo.o:(.rodata.__go_tdn_example.main..example_main._Ctype_int+0x20): undefined reference to `__go_type_equal_identity'
foo.o:(.rodata.__go_td_pN30_example.main._Ctype_struct_num[__go_td_pN30_example.main._Ctype_struct_num]+0x18): undefined reference to `__go_type_hash_identity'
foo.o:(.rodata.__go_td_pN30_example.main._Ctype_struct_num[__go_td_pN30_example.main._Ctype_struct_num]+0x20): undefined reference to `__go_type_equal_identity'
foo.o:(.rodata.__go_tdn_example.main..example_main._Ctype_struct_num+0x18): undefined reference to `__go_type_hash_identity'
foo.o:(.rodata.__go_tdn_example.main..example_main._Ctype_struct_num+0x20): undefined reference to `__go_type_equal_identity'
foo.o:(.rodata.__go_td_pN24_example.main._Ctype_void[__go_td_pN24_example.main._Ctype_void]+0x18): undefined reference to `__go_type_hash_identity'
foo.o:(.rodata.__go_td_pN24_example.main._Ctype_void[__go_td_pN24_example.main._Ctype_void]+0x20): undefined reference to `__go_type_equal_identity'
foo.o:(.rodata.__go_tdn_example.main..example_main._Ctype_void+0x18): undefined reference to `__go_type_hash_identity'
foo.o:(.rodata.__go_tdn_example.main..example_main._Ctype_void+0x20): undefined reference to `__go_type_equal_identity'
collect2: error: ld returned 1 exit status
Makefile:4: recipe for target 'main' failed
make: *** [main] Error 1
From what I understand from other searches, these errors relate to the calls made to the C go library, indicating this may not be getting compiled into the object file. I've tried running gccgo directly in the make file as well with the same results. Any insight and/or assistance is appreciated. Thanks.
Edit
I figured this out thanks to this post. Apparently I needed to call gccgo for main in the Makefile since gcc doesn't know how to properly link the go runtime.