GCC 10 will now error when declaring a global variable twice: https://gcc.gnu.org/gcc-10/porting_to.html#common Fix this issue by declaring the variable as `extern' in `krt.h'. The variable is really declared in `krt.c'. LD -r -o all.o cf-parse.tab.o cf-lex.o conf.o /usr/bin/ld: cf-lex.o:/home/bernat/code/exoscale/bird/build~/conf/../lib/krt.h:115: multiple definition of `kif_proto'; cf-parse.tab.o:/home/bernat/code/exoscale/bird/build~/conf/../lib/krt.h:115: first defined here This issue was already fixed in BIRD 2.x. --- sysdep/unix/krt.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/sysdep/unix/krt.h b/sysdep/unix/krt.h index d4a8717e38ec..fe79efc3717d 100644 --- a/sysdep/unix/krt.h +++ b/sysdep/unix/krt.h @@ -112,7 +112,7 @@ struct kif_proto { struct kif_state sys; /* Sysdep state */ }; -struct kif_proto *kif_proto; +extern struct kif_proto *kif_proto; #define KIF_CF ((struct kif_config *)p->p.cf) -- 2.28.0