From 78bbd585451752e7b23eafbfa1dc009fd5cda750 Mon Sep 17 00:00:00 2001
From: Brad King <brad.king@kitware.com>
Date: Thu, 27 Jul 2023 11:01:48 -0400
Subject: Source: Link libatomic when needed on Linux 32-bit ARM

Fixes: #25114
---
 Source/CMakeLists.txt                   | 10 +++-------
 Source/Checks/cm_cxx_atomic.cxx         |  6 ++++++
 Source/Checks/cm_cxx_atomic_builtin.cxx |  1 +
 Source/Checks/cm_cxx_atomic_lib.cxx     |  1 +
 Source/Checks/cm_cxx_features.cmake     | 11 +++++++++++
 Utilities/cmcppdap/CMakeLists.txt       |  3 +++
 6 files changed, 25 insertions(+), 7 deletions(-)
 create mode 100644 Source/Checks/cm_cxx_atomic.cxx
 create mode 100644 Source/Checks/cm_cxx_atomic_builtin.cxx
 create mode 100644 Source/Checks/cm_cxx_atomic_lib.cxx

diff --git a/Source/CMakeLists.txt b/Source/CMakeLists.txt
index b01e1e7..f022dda 100644
--- a/Source/CMakeLists.txt
+++ b/Source/CMakeLists.txt
@@ -938,13 +938,9 @@ if(WIN32 AND NOT CYGWIN)
   list(APPEND _tools cmcldeps)
 endif()
 
-if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND CMAKE_SYSTEM_PROCESSOR MATCHES "sparc")
-  # the atomic instructions are implemented using libatomic on some platforms,
-  # so linking to that may be required
-  check_library_exists(atomic __atomic_fetch_add_4 "" LIBATOMIC_NEEDED)
-  if(LIBATOMIC_NEEDED)
-    target_link_libraries(CMakeLib PUBLIC atomic)
-  endif()
+# Some atomic instructions are implemented using libatomic on some platforms.
+if(CMake_HAVE_CXX_ATOMIC_LIB)
+  target_link_libraries(CMakeLib PUBLIC atomic)
 endif()
 
 # On Apple we need CoreFoundation and CoreServices
diff --git a/Source/Checks/cm_cxx_atomic.cxx b/Source/Checks/cm_cxx_atomic.cxx
new file mode 100644
index 0000000..098a7a7
--- /dev/null
+++ b/Source/Checks/cm_cxx_atomic.cxx
@@ -0,0 +1,6 @@
+#include <atomic>
+int main()
+{
+  std::atomic<long long>(0).load();
+  return 0;
+}
diff --git a/Source/Checks/cm_cxx_atomic_builtin.cxx b/Source/Checks/cm_cxx_atomic_builtin.cxx
new file mode 100644
index 0000000..d284f6c
--- /dev/null
+++ b/Source/Checks/cm_cxx_atomic_builtin.cxx
@@ -0,0 +1 @@
+#include "cm_cxx_atomic.cxx"
diff --git a/Source/Checks/cm_cxx_atomic_lib.cxx b/Source/Checks/cm_cxx_atomic_lib.cxx
new file mode 100644
index 0000000..d284f6c
--- /dev/null
+++ b/Source/Checks/cm_cxx_atomic_lib.cxx
@@ -0,0 +1 @@
+#include "cm_cxx_atomic.cxx"
diff --git a/Source/Checks/cm_cxx_features.cmake b/Source/Checks/cm_cxx_features.cmake
index f5b7587..98d5eff 100644
--- a/Source/Checks/cm_cxx_features.cmake
+++ b/Source/Checks/cm_cxx_features.cmake
@@ -17,6 +17,7 @@ function(cm_check_cxx_feature name)
       try_run(CMake_RUN_CXX_${FEATURE} CMake_COMPILE_CXX_${FEATURE}
         ${CMAKE_CURRENT_BINARY_DIR}
         ${CMAKE_CURRENT_LIST_DIR}/cm_cxx_${name}.cxx
+        LINK_LIBRARIES ${cm_check_cxx_feature_LINK_LIBRARIES}
         CMAKE_FLAGS ${maybe_cxx_standard}
         OUTPUT_VARIABLE OUTPUT
         )
@@ -29,6 +30,7 @@ function(cm_check_cxx_feature name)
       try_compile(CMake_HAVE_CXX_${FEATURE}
         ${CMAKE_CURRENT_BINARY_DIR}
         ${CMAKE_CURRENT_LIST_DIR}/cm_cxx_${name}.cxx
+        LINK_LIBRARIES ${cm_check_cxx_feature_LINK_LIBRARIES}
         CMAKE_FLAGS ${maybe_cxx_standard}
         OUTPUT_VARIABLE OUTPUT
         )
@@ -93,3 +95,12 @@ if (NOT CMAKE_CXX_STANDARD LESS "17")
 else()
   set(CMake_HAVE_CXX_FILESYSTEM FALSE)
 endif()
+
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND CMAKE_SYSTEM_PROCESSOR MATCHES "armv7l|sparc")
+  cm_check_cxx_feature(atomic_builtin)
+  if(NOT CMake_HAVE_CXX_ATOMIC_BUILTIN)
+    set(cm_check_cxx_feature_LINK_LIBRARIES atomic)
+    cm_check_cxx_feature(atomic_lib) # defines CMake_HAVE_CXX_ATOMIC_LIB
+    unset(cm_check_cxx_feature_LINK_LIBRARIES)
+  endif()
+endif()
diff --git a/Utilities/cmcppdap/CMakeLists.txt b/Utilities/cmcppdap/CMakeLists.txt
index 39f72a2..b6841f1 100644
--- a/Utilities/cmcppdap/CMakeLists.txt
+++ b/Utilities/cmcppdap/CMakeLists.txt
@@ -33,5 +33,8 @@ if(WIN32)
 elseif(NOT APPLE)
   target_link_libraries(cmcppdap PRIVATE Threads::Threads)
 endif()
+if(CMake_HAVE_CXX_ATOMIC_LIB)
+  target_link_libraries(cmcppdap PRIVATE atomic)
+endif()
 
 install(FILES NOTICE DESTINATION ${CMAKE_DOC_DIR}/cmcppdap)
-- 
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