From 4da54b6be6a1ca19a2026908d48ae5c8d327ec86 Mon Sep 17 00:00:00 2001 From: Samuel Martin Date: Thu, 26 May 2016 23:46:40 +0200 Subject: [PATCH] cmake: add check for explicit linking against libatomic To use atomics functions, some toolchains requires to explicitly add -latomic to the linker flags (because they are not provided by libc, but libatomic). This change adds a helper function trying to build/link a test program using atomics, then calls it to: * first check if atomics are directly available in the libc; * if not and libatomic has been found, then run the same test with "-latomic" added to the linker flags. The pulseview link library list is updated according to the results of these tests. This issue was triggered by the Buildroot farms: http://autobuild.buildroot.org/results/1e3/1e3101261252d5f30fdf842cc99604e4f4c25eef/build-end.log Notes: 1- CMAKE_REQUIRED_* variables are only used in check functions. They are not automatically forwarded to/handled by the target commands (such as target_link_library), because the check functions are implemented as macro in CMake code, whereas many target commands are native. 2- Because of note #1, CMAKE_REQUIRED_LIBRARIES (or its value) must be explicitly passed to the target_link_library command when this is needed. 3- In this implementation, LIBATOMIC_LIBRARY is only set when it is needed; so, unconditionally appending it to PULSEVIEW_LINK_LIBS will produce the expected behavior. This fixes bug #810. Signed-off-by: Samuel Martin --- CMakeLists.txt | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) diff --git a/CMakeLists.txt b/CMakeLists.txt index 9dac69f2..44f810e3 100644 --- a/CMakeLists.txt +++ b/CMakeLists.txt @@ -107,6 +107,55 @@ endif() # This will set ${CMAKE_THREAD_LIBS_INIT} to the correct, OS-specific value. find_package(Threads REQUIRED) + +# Check for explicit link against libatomic +# +# Depending on the toolchain, linking a program using atomic functions may need +# "-latomic" explicitly passed to the linker +# +# This check first tests if atomics are available in the C-library, if not and +# libatomic exists, then it runs the same test with -latomic added to the +# linker flags. + +# Helper for checking for atomics +function(check_working_cxx_atomics varname additional_lib) + include(CheckCXXSourceCompiles) + include(CMakePushCheckState) + cmake_push_check_state() + set(CMAKE_REQUIRED_FLAGS "-std=c++11") + set(CMAKE_REQUIRED_LIBRARIES "${additional_lib}") + set(CMAKE_REQUIRED_QUIET 1) + CHECK_CXX_SOURCE_COMPILES(" +#include +std::atomic x; +int main() { + return std::atomic_fetch_add_explicit(&x, 1, std::memory_order_seq_cst); +} +" ${varname}) + cmake_pop_check_state() +endfunction(check_working_cxx_atomics) + +# First check if atomics work without the library. +# If not, check if the library exists, and atomics work with it. +check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITHOUT_LIB "") +if(HAVE_CXX_ATOMICS_WITHOUT_LIB) + message(STATUS "Atomics provided by the C-library - yes") +else() + message(STATUS "Atomics provided by the C-library - no") + find_library(LIBATOMIC_LIBRARY NAMES atomic PATH_SUFFIXES lib) + if(LIBATOMIC_LIBRARY) + check_working_cxx_atomics(HAVE_CXX_ATOMICS_WITH_LIB "${LIBATOMIC_LIBRARY}") + if (HAVE_CXX_ATOMICS_WITH_LIB) + message(STATUS "Atomics provided by libatomic - yes") + else() + message(STATUS "Atomics provided by libatomic - no") + message(FATAL_ERROR "Compiler must support std::atomic!") + endif() + else() + message(FATAL_ERROR "Compiler appears to require libatomic, but cannot find it.") + endif() +endif() + #=============================================================================== #= System Introspection #------------------------------------------------------------------------------- @@ -387,6 +436,7 @@ set(PULSEVIEW_LINK_LIBS ${Boost_LIBRARIES} ${QT_LIBRARIES} ${CMAKE_THREAD_LIBS_INIT} + ${LIBATOMIC_LIBRARY} ) if(STATIC_PKGDEPS_LIBS) -- 2.30.2