[PATCH v2 2/2] meson: fix CONFIG_ATOMIC128 check

[marcandre . lureau]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

The current testing code isn't correct and matching QEMU usage:

testfile.c: In function 'main':
testfile.c:5:11: error: incorrect number of arguments to function 
'__atomic_load'
    5 |       y = __atomic_load(&x, 0);
      |           ^~~~~~~~~~~~~
testfile.c:6:7: error: argument 2 of '__atomic_store' must be a pointer type
    6 |       __atomic_store(&x, y, 0);
      |       ^~~~~~~~~~~~~~
testfile.c:7:7: error: argument 3 of '__atomic_compare_exchange' must be a 
pointer type
    7 |       __atomic_compare_exchange(&x, &y, x, 0, 0, 0);
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~

Replace the test with common atomics test for u64 and u128 that matches
better QEMU needs.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 meson.build | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/meson.build b/meson.build
index a9ec3974bc67..893eaa8ff971 100644
--- a/meson.build
+++ b/meson.build
@@ -1808,21 +1808,23 @@ config_host_data.set('HAVE_BROKEN_SIZE_MAX', not 
cc.compiles('''
         return printf("%zu", SIZE_MAX);
     }''', args: ['-Werror']))
 
-# See if 64-bit atomic operations are supported.
-# Note that without __atomic builtins, we can only
-# assume atomic loads/stores max at pointer size.
-config_host_data.set('CONFIG_ATOMIC64', cc.links('''
+atomic_test = '''
   #include <stdint.h>
   int main(void)
   {
-    uint64_t x = 0, y = 0;
+    @0@ x = 0, y = 0;
     y = __atomic_load_n(&x, __ATOMIC_RELAXED);
     __atomic_store_n(&x, y, __ATOMIC_RELAXED);
     __atomic_compare_exchange_n(&x, &y, x, 0, __ATOMIC_RELAXED, 
__ATOMIC_RELAXED);
     __atomic_exchange_n(&x, y, __ATOMIC_RELAXED);
     __atomic_fetch_add(&x, y, __ATOMIC_RELAXED);
     return 0;
-  }'''))
+  }'''
+
+# See if 64-bit atomic operations are supported.
+# Note that without __atomic builtins, we can only
+# assume atomic loads/stores max at pointer size.
+config_host_data.set('CONFIG_ATOMIC64', 
cc.links(atomic_test.format('uint64_t')))
 
 has_int128 = cc.links('''
   __int128_t a;
@@ -1837,15 +1839,10 @@ has_int128 = cc.links('''
 config_host_data.set('CONFIG_INT128', has_int128)
 
 if has_int128
-  has_atomic128 = cc.links('''
-    int main(void)
-    {
-      unsigned __int128 x = 0, y = 0;
-      y = __atomic_load(&x, 0);
-      __atomic_store(&x, y, 0);
-      __atomic_compare_exchange(&x, &y, x, 0, 0, 0);
-      return 0;
-    }''')
+  # "do we have 128-bit atomics which are handled inline and specifically not
+  # via libatomic". The reason we can't use libatomic is documented in the
+  # comment starting "GCC is a house divided" in include/qemu/atomic128.h.
+  has_atomic128 = cc.links(atomic_test.format('unsigned __int128'))
 
   config_host_data.set('CONFIG_ATOMIC128', has_atomic128)
 
-- 
2.35.1.273.ge6ebfd0e8cbb