net/sfc: fix build with clang 3.4.2

Old clang requires libatomic as well as gcc. Avoid compiler name and
version based checks. Add custom test for 16-byte atomic operations
to find out if libatomic is required to build.

Bugzilla ID: 760
Fixes: 96fd2bd69b58 ("net/sfc: support flow action count in transfer rules")

Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: David Marchand <david.marchand@redhat.com>

diff --git a/drivers/net/sfc/meson.build b/drivers/net/sfc/meson.build
index 4625859..a1ad792 100644 (file)
--- a/drivers/net/sfc/meson.build
+++ b/drivers/net/sfc/meson.build
@@ -40,8 +40,20 @@ foreach flag: extra_flags
     endif
 endforeach
 
-# for gcc compiles we need -latomic for 128-bit atomic ops
-if cc.get_id() == 'gcc'
+# for gcc and old Clang compiles we need -latomic for 128-bit atomic ops
+atomic_check_code = '''
+int main(void)
+{
+    __int128 a = 0;
+    __int128 b;
+
+    b = __atomic_load_n(&a, __ATOMIC_RELAXED);
+    __atomic_store(&b, &a, __ATOMIC_RELAXED);
+    __atomic_store_n(&b, a, __ATOMIC_RELAXED);
+    return 0;
+}
+'''
+if not cc.links(atomic_check_code)
     libatomic_dep = cc.find_library('atomic', required: false)
     if not libatomic_dep.found()
         build = false
@@ -51,11 +63,7 @@ if cc.get_id() == 'gcc'
 
     # libatomic could be half-installed when above check finds it but
     # linkage fails
-    atomic_link_code = '''
-    #include <stdio.h>
-    void main() { printf("libatomic link check\n"); }
-    '''
-    if not cc.links(atomic_link_code, dependencies: libatomic_dep)
+    if not cc.links(atomic_check_code, dependencies: libatomic_dep)
         build = false
         reason = 'broken dependency, "libatomic"'
         subdir_done()