At least the GHashTable is an incomplete type. This breaks the GDB pretty printer which does not know the fields of the struct. Result: the pretty printer throws a GDB error and is pretty much useless.

Tested with GDB 7.7 on Arch Linux

$ cat > n.c <<EOF
#include <glib.h>

int main() {
    GHashTable *ht;

    ht = g_hash_table_new(g_str_hash, g_str_equal);
    g_hash_table_insert(ht, "foo", "bar");
    g_hash_table_insert(ht, "ffs", "omg");
    return 0;
}
EOF
$ gcc $(pkg-config --cflags glib-2.0) n.c -g $(pkg-config --libs glib-2.0)
$ gdb -q -ex 'break 9' -ex r -ex 'p ht' -ex c -ex q ./a.out
...
Breakpoint 1, main () at n.c:9
9           return 0;
Python Exception <class 'gdb.error'> There is no member named keys.: 
$1 = 0x602000
Continuing.