From 56b40a8f055cfd05633054aed5d3466a6e058b72 Mon Sep 17 00:00:00 2001
From: Ben Wolsieffer <benwolsieffer@gmail.com>
Date: Thu, 4 Oct 2018 20:25:10 -0400
Subject: [PATCH] Link to libatomic when necessary (eg. on armv6l)

---
 configure.ac    | 16 ++++++++++++++++
 src/Makefile.am |  4 ++--
 tests.sh        |  4 ++--
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/configure.ac b/configure.ac
index 8e1c308ce1..18a77f5977 100644
--- a/configure.ac
+++ b/configure.ac
@@ -165,6 +165,22 @@ AS_IF([test "$with_zlib" != no], [
 ])
 AM_CONDITIONAL([HAVE_ZLIB], [test $HAVE_ZLIB = 1])
 
+dnl On some platforms, std::atomic needs a helper library
+AC_MSG_CHECKING(whether -latomic is needed)
+AC_LINK_IFELSE([AC_LANG_SOURCE([[
+  #include <atomic>
+  #include <cstdint>
+  std::atomic<std::int64_t> v;
+  int main() {
+    return v;
+  }
+]])], STD_ATOMIC_NEED_LIBATOMIC=no, STD_ATOMIC_NEED_LIBATOMIC=yes)
+AC_MSG_RESULT($STD_ATOMIC_NEED_LIBATOMIC)
+if test "x$STD_ATOMIC_NEED_LIBATOMIC" = xyes; then
+  LIBATOMIC_LIBS="-latomic"
+fi
+AC_SUBST([LIBATOMIC_LIBS])
+
 AS_IF([test "$with_protoc" != "no"], [
   PROTOC=$with_protoc
   AS_IF([test "$with_protoc" = "yes"], [
diff --git a/src/Makefile.am b/src/Makefile.am
index bfa0d3ad1b..24c63669fd 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -166,7 +166,7 @@ nobase_include_HEADERS =                                         \
 
 lib_LTLIBRARIES = libprotobuf-lite.la libprotobuf.la libprotoc.la
 
-libprotobuf_lite_la_LIBADD = $(PTHREAD_LIBS)
+libprotobuf_lite_la_LIBADD = $(PTHREAD_LIBS) $(LIBATOMIC_LIBS)
 libprotobuf_lite_la_LDFLAGS = -version-info 17:0:0 -export-dynamic -no-undefined
 if HAVE_LD_VERSION_SCRIPT
 libprotobuf_lite_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libprotobuf-lite.map
@@ -212,7 +212,7 @@ libprotobuf_lite_la_SOURCES =                                  \
   google/protobuf/io/zero_copy_stream.cc                       \
   google/protobuf/io/zero_copy_stream_impl_lite.cc
 
-libprotobuf_la_LIBADD = $(PTHREAD_LIBS)
+libprotobuf_la_LIBADD = $(PTHREAD_LIBS) $(LIBATOMIC_LIBS)
 libprotobuf_la_LDFLAGS = -version-info 17:0:0 -export-dynamic -no-undefined
 if HAVE_LD_VERSION_SCRIPT
 libprotobuf_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libprotobuf.map
diff --git a/tests.sh b/tests.sh
index fc7c95c4d6..df41bc5a61 100755
--- a/tests.sh
+++ b/tests.sh
@@ -16,8 +16,8 @@ internal_build_cpp() {
   git submodule update --init --recursive
 
   ./autogen.sh
-  ./configure CXXFLAGS="-fPIC"  # -fPIC is needed for python cpp test.
-                                # See python/setup.py for more details
+  ./configure CXXFLAGS="-fPIC -std=c++11"  # -fPIC is needed for python cpp test.
+                                           # See python/setup.py for more details
   make -j4
 }