CMakeLists: autodetect libatomic

build/CMakeLists.txt

@@ -83,7 +83,7 @@ if (WITH_WEBSOCKETS)
   find_package(websocketpp REQUIRED)
 endif ()
 
-if (CMAKE_SYSTEM_NAME STREQUAL "Windows" OR MSYS)
+if (WIN32 OR MSYS)
   list (APPEND LIBI2PD_SRC "${CMAKE_SOURCE_DIR}/I2PEndian.cpp")
 endif ()
 
@@ -194,19 +194,13 @@ if (WITH_HARDENING AND MSVC)
 endif ()
 
 # compiler flags customization (by system)
-if (CMAKE_SYSTEM_NAME STREQUAL "Linux")
+if (UNIX)
   list (APPEND DAEMON_SRC "${DAEMON_SRC_DIR}/UnixDaemon.cpp")
+  if (NOT (CMAKE_SYSTEM_NAME STREQUAL "OpenBSD" OR APPLE))
     # "'sleep_for' is not a member of 'std::this_thread'" in gcc 4.7/4.8
     add_definitions( "-D_GLIBCXX_USE_NANOSLEEP=1" )
-elseif (CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
-  list (APPEND DAEMON_SRC "${DAEMON_SRC_DIR}/UnixDaemon.cpp")
-  # "'sleep_for' is not a member of 'std::this_thread'" in gcc 4.7/4.8
-  add_definitions( "-D_GLIBCXX_USE_NANOSLEEP=1" )
-elseif (CMAKE_SYSTEM_NAME STREQUAL "Darwin")
-    list (APPEND DAEMON_SRC "${DAEMON_SRC_DIR}/UnixDaemon.cpp")
-  elseif (CMAKE_SYSTEM_NAME STREQUAL "OpenBSD")
-      list (APPEND DAEMON_SRC "${DAEMON_SRC_DIR}/UnixDaemon.cpp")
-    elseif (CMAKE_SYSTEM_NAME STREQUAL "Windows" OR MSYS)
+  endif ()
+elseif (WIN32 OR MSYS)
   list (APPEND DAEMON_SRC "${CMAKE_SOURCE_DIR}/Win32/DaemonWin32.cpp")
   if (WITH_GUI)
     list (APPEND DAEMON_SRC "${CMAKE_SOURCE_DIR}/Win32/Win32App.cpp")
@@ -263,6 +257,8 @@ if(THREADS_HAVE_PTHREAD_ARG) # compile time flag
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
 endif()
 
+include(CheckLibcxxAtomic)
+
 if (WITH_STATIC)
   set(Boost_USE_STATIC_LIBS ON)
   set(Boost_USE_STATIC_RUNTIME ON)
@@ -370,11 +366,13 @@ if (NOT ZLIB_FOUND )
   if (NOT WITH_STATIC)
     set ( ZLIB_LIBRARY debug zlibd optimized zlib CACHE STRING "zlib libraries" FORCE)
   endif ()
+  link_directories(${CMAKE_CURRENT_BINARY_DIR}/zlib/lib)
+else()
+  link_directories(${ZLIB_ROOT}/lib)
 endif ()
 if (WITH_STATIC AND (MSVC OR MSYS))
   set ( ZLIB_LIBRARY debug zlibstaticd optimized zlibstatic CACHE STRING "zlib libraries" FORCE)
 endif ()
-link_directories(${CMAKE_CURRENT_BINARY_DIR}/zlib/lib ${ZLIB_ROOT}/lib)
 
 # load includes
 include_directories( SYSTEM ${Boost_INCLUDE_DIRS} ${OPENSSL_INCLUDE_DIR} ${ZLIB_INCLUDE_DIR} )

build/cmake_modules/CheckLibcxxAtomic.cmake

@@ -0,0 +1,47 @@
+INCLUDE(CheckCXXSourceCompiles)
+
+# Sometimes linking against libatomic is required for atomic ops, if
+# the platform doesn't support lock-free atomics.
+#
+# We could modify LLVM's CheckAtomic module and have it check for 64-bit
+# atomics instead. However, we would like to avoid careless uses of 64-bit
+# atomics inside LLVM over time on 32-bit platforms.
+
+function(check_cxx_atomics varname)
+  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+  set(CMAKE_REQUIRED_FLAGS "-nodefaultlibs -std=c++11 -nostdinc++ -isystem ${LIBCXX_SOURCE_DIR}/include")
+  if (${LIBCXX_GCC_TOOLCHAIN})
+    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} --gcc-toolchain=${LIBCXX_GCC_TOOLCHAIN}")
+  endif()
+  if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
+    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
+  endif()
+  if (CMAKE_C_FLAGS MATCHES -fsanitize-coverage OR CMAKE_CXX_FLAGS MATCHES -fsanitize-coverage)
+    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize-coverage=edge,trace-cmp,indirect-calls,8bit-counters")
+  endif()
+  check_cxx_source_compiles("
+#include <cstdint>
+#include <atomic>
+std::atomic<uintptr_t> x;
+std::atomic<uintmax_t> y;
+int main() {
+  return x + y;
+}
+" ${varname})
+  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
+endfunction(check_cxx_atomics)
+
+check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
+check_library_exists(atomic __atomic_fetch_add_8 "" LIBCXX_HAS_ATOMIC_LIB)
+# If not, check if the library exists, and atomics work with it.
+if(NOT LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB)
+  if(LIBCXX_HAS_ATOMIC_LIB)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES "atomic")
+    check_cxx_atomics(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
+    if (NOT LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
+      message(WARNING "Host compiler must support std::atomic!")
+    endif()
+  else()
+    message(WARNING "Host compiler appears to require libatomic, but cannot find it.")
+  endif()
+endif()