configure: check if -latomic is needed for __atomic_*

On some platforms, gcc generates library calls when __atomic_* functions
are used, but does not link the required library (libatomic) automatically
(supposedly to allow the app to use some other atomics implementation?).

Detect this at configure time and add the library when needed. Tested
on armel (library was added) and on x86_64 (was not, as expected).

Some documentation on this is provided in GCC wiki:
https://gcc.gnu.org/wiki/Atomic/GCCMM

Fixes: 8915f0c0 "util: use GCC atomic intrinsics with explicit memory model"
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102573
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

diff --git a/configure.ac b/configure.ac
index f5d960f9d92c8a235c02b59a761b18b50c5a1dc6..d87b76703392e5058f6becef98d22aae37b1f5ba 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -379,8 +379,21 @@ int main() {
 }]])], GCC_ATOMIC_BUILTINS_SUPPORTED=1)
 if test "x$GCC_ATOMIC_BUILTINS_SUPPORTED" = x1; then
     DEFINES="$DEFINES -DUSE_GCC_ATOMIC_BUILTINS"
+    dnl On some platforms, new-style atomics need a helper library
+    AC_MSG_CHECKING(whether -latomic is needed)
+    AC_LINK_IFELSE([AC_LANG_SOURCE([[
+    #include <stdint.h>
+    uint64_t v;
+    int main() {
+        return (int)__atomic_load_n(&v, __ATOMIC_ACQUIRE);
+    }]])], GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC=no, GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC=yes)
+    AC_MSG_RESULT($GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC)
+    if test "x$GCC_ATOMIC_BUILTINS_NEED_LIBATOMIC" = xyes; then
+        LIBATOMIC_LIBS="-latomic"
+    fi
 fi
 AM_CONDITIONAL([GCC_ATOMIC_BUILTINS_SUPPORTED], [test x$GCC_ATOMIC_BUILTINS_SUPPORTED = x1])
+AC_SUBST([LIBATOMIC_LIBS])
 
 dnl Check if host supports 64-bit atomics
 dnl note that lack of support usually results in link (not compile) error

diff --git a/src/util/Makefile.am b/src/util/Makefile.am
index 9885bbe9685b3d702057a00a53a6edb2a605bade..c37afff75200e21fa5a549ef1ae99ec7e62bdd88 100644 (file)
--- a/src/util/Makefile.am
+++ b/src/util/Makefile.am
@@ -48,7 +48,8 @@ libmesautil_la_SOURCES = \
 
 libmesautil_la_LIBADD = \
        $(CLOCK_LIB) \
-       $(ZLIB_LIBS)
+       $(ZLIB_LIBS) \
+       $(LIBATOMIC_LIBS)
 
 libxmlconfig_la_SOURCES = $(XMLCONFIG_FILES)
 libxmlconfig_la_CFLAGS = \