[GNUnet-developers] [RFC] util: build with external libatomic

[Daniel Golle]

Recent versions of gcc on some architectures (MIPS, PPC, ...) moved
atomic functions into a separate library. As we are using atomic
load/store in util/time.c we may need to link libgnunetutil against
libatomic for __atomic_load_8 and __atomic_store_8 to be defined.

Fixes build problem on MIPS:
ld: ./.libs/libgnunetutil.so: undefined reference to `__atomic_store_8'
ld: ./.libs/libgnunetutil.so: undefined reference to `__atomic_load_8'
collect2: error: ld returned 1 exit status

This patch, however, causes an endless number of
libtool: relink: warning: 
`/usr/src/lede/staging_dir/toolchain-mipsel_24kc_gcc-7.4.0_musl/lib/libatomic.la'
 seems to be moved
lines printed during build and almost every shared library is linked
against libatomic in the end (though it would really only be needed
for libgnunetutil). Apparently libtool's dependency_libs is the problem
or at least that's where the absolute path of libatomic.la in LIBS
comes from. I was trying to resolve this autotools mess for 2 hours now
and didn't manage to *not* have libtool care about libatomic.

Ideas?
---
 configure.ac         | 7 ++++++-
 src/util/Makefile.am | 7 +++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 8b93d8d6c..00437f2ef 100644
--- a/configure.ac
+++ b/configure.ac
@@ -676,6 +677,8 @@ else
        AC_DEFINE([HAVE_LIBCURL],[1],[Have CURL])
 fi
 
+AC_SEARCH_LIBS(__atomic_load_8, atomic, [have_libatomic=1 
AC_DEFINE(HAVE_LIBATOMIC,1,[external libatomic])])
+AM_CONDITIONAL(HAVE_LIBATOMIC, [test "$have_libatomic" = 1])
 
 # restore LIBS & CPPFLAGS
 LIBS=$SAVE_LIBS
diff --git a/src/util/Makefile.am b/src/util/Makefile.am
index 0ba06f4bb..5fa6e907e 100644
--- a/src/util/Makefile.am
+++ b/src/util/Makefile.am
@@ -123,6 +123,12 @@ libgnunetutil_la_SOURCES = \
   speedup.c speedup.h \
        proc_compat.c
 
+if HAVE_LIBATOMIC
+  LIBATOMIC= -latomic
+else
+  LIBATOMIC=
+endif
+
 if HAVE_LIBIDN
   LIBIDN= -lidn
 else
@@ -137,6 +143,7 @@ endif
 
 libgnunetutil_la_LIBADD = \
   $(GCLIBADD) $(WINLIB) \
+  $(LIBATOMIC) \
   $(LIBGCRYPT_LIBS) \
   $(LTLIBICONV) \
   $(LTLIBINTL) \
-- 
2.20.1