[Mesa-dev] [PATCH] disk cache: Link with -latomic if necessary

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

The disk cache implementation uses 64-bit atomic operations. For some
architectures, such as 32-bit ARM, GCC will not be able to translate
these operations into lock-free instructions and will instead rely on
the external atomics library to provide these operations.

Check at configuration time whether or not linking against libatomic
is necessary and if so, create a dependency that can be used while
linking the mesautil library.

This is the meson equivalent of 2ef7f23820a6 ("configure: check if
-latomic is needed for __atomic_*").

Signed-off-by: Thierry Reding <treding at nvidia.com>
---
 meson.build          | 15 +++++++++++++++
 src/util/meson.build |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/meson.build b/meson.build
index 121341a950c4..7c6f40573421 100644
--- a/meson.build
+++ b/meson.build
@@ -800,6 +800,21 @@ endif
 if cc.compiles('int main() { int n; return __atomic_load_n(&n, __ATOMIC_ACQUIRE); }',
                name : 'GCC atomic builtins')
   pre_args += '-DUSE_GCC_ATOMIC_BUILTINS'
+
+  # Not all atomic calls can be turned into lock-free instructions, in which
+  # GCC will make calls into the libatomic library. Check whether we need to
+  # link with -latomic.
+  #
+  # This can happen for 64-bit atomic operations on 32-bit architectures such
+  # as ARM.
+  if not cc.links('''#include <stdint.h>
+                     int main() {
+                       uint64_t n;
+                       return (int)__atomic_load_n(&n, __ATOMIC_ACQUIRE);
+                     }''',
+                  name : 'GCC atomic builtins required -latomic')
+    dep_atomic = cc.find_library('atomic')
+  endif
 endif
 if not cc.links('''#include <stdint.h>
                    uint64_t v;
diff --git a/src/util/meson.build b/src/util/meson.build
index b23dba3a9851..eece1cefef6a 100644
--- a/src/util/meson.build
+++ b/src/util/meson.build
@@ -102,7 +102,7 @@ libmesa_util = static_library(
   'mesa_util',
   [files_mesa_util, format_srgb],
   include_directories : inc_common,
-  dependencies : [dep_zlib, dep_clock, dep_thread],
+  dependencies : [dep_zlib, dep_clock, dep_thread, dep_atomic],
   c_args : [c_msvc_compat_args, c_vis_args],
   build_by_default : false
 )
-- 
2.16.2