Hi,
We've run into a problem trying to compile openvswitch with CFLAGS=-Werror.
I don't think it's an openvswitch problem. It appears to be a
autoconf/gcc issue.
openvswitch has a test to detect the library that implements
__atomic_load_8 which boils down to "AC_SEARCH_LIBS([__atomic_load_8],
[atomic])". The problem is when configure is invoked with
"CFLAGS=-Werror ./configure" conftest.c fails to compile because the
dummy prototype used doesn't match the builtin definition. This in turn
causes openvswitch to fail to link because -latomic isn't included in LIBS.
Here is a small patch that illustrates the problem
--- 8< ---
diff --git a/Makefile.am b/Makefile.am
new file mode 100644
index 0000000..e69de29
diff --git a/configure.ac b/configure.ac
new file mode 100644
index 0000000..0607b5b
--- /dev/null
+++ b/configure.ac
@@ -0,0 +1,10 @@
+AC_INIT([test], [0.1])
+AM_INIT_AUTOMAKE([-Wall -Werror foreign])
+AC_CONFIG_HEADERS([config.h])
+AC_PROG_CC
+AC_SEARCH_LIBS([__atomic_load_8], [atomic])
+AC_CONFIG_FILES([
+ Makefile
+])
+AC_OUTPUT
+
--- 8< ---
When invoked without specifying CFLAGS I get the following
$ autoreconf -fvi
$ ./configure | grep atomic_load
checking for library containing __atomic_load_8... -latomic
When specifing -Werror I get
$ autoreconf -fvi
$ CFLAGS=-Werror ./configure | grep atomic_load
checking for library containing __atomic_load_8... no
Looking at config.log we can see the following
generated by GNU Autoconf 2.69.
...
configure:2742: checking for C compiler version
configure:2751: gcc --version >&5
gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
...
configure:3478: checking for library containing __atomic_load_8
configure:3509: gcc -o conftest -Werror conftest.c >&5
conftest.c:18:6: error: conflicting types for built-in function
'__atomic_load_8' [-Werror]
char __atomic_load_8 ();
^
cc1: all warnings being treated as errors
Any thoughts on how we can get -latomic detected and -Werror passed
through to the build?
