[Buildroot] [PATCH v2] package/pulseview: fix build when linking against libatomic is needed

[Romain Naour <romain.naour@gmail.com>]

Hi Samuel, Thomas, All,

Le 27/05/2016 ? 00:00, Samuel Martin a ?crit :
> With some toolchains, using atomics requires to explicitly add -latomic
> to the linker flags.
> 
> This change adds a patch to pulseview adding this detection and updating
> the LDFLAGS when appropriate.
> 
> This patch has be sent upstream:
>   http://article.gmane.org/gmane.comp.debugging.sigrok.devel/2097
> 
> Fixes:
>   http://autobuild.buildroot.org/results/1e3/1e3101261252d5f30fdf842cc99604e4f4c25eef/build-end.log
> 
> Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> Cc: Romain Naour <romain.naour@gmail.com>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Signed-off-by: Samuel Martin <s.martin49@gmail.com>
> 
> ---
> changes v1->v2:
> - update/rework pulseview patch
> ---
>  ...heck-for-explicit-linking-against-libatom.patch | 117 +++++++++++++++++++++
>  1 file changed, 117 insertions(+)
>  create mode 100644 package/pulseview/0002-cmake-add-check-for-explicit-linking-against-libatom.patch
> 
> diff --git a/package/pulseview/0002-cmake-add-check-for-explicit-linking-against-libatom.patch b/package/pulseview/0002-cmake-add-check-for-explicit-linking-against-libatom.patch
> new file mode 100644
> index 0000000..70549e6
> --- /dev/null
> +++ b/package/pulseview/0002-cmake-add-check-for-explicit-linking-against-libatom.patch
> @@ -0,0 +1,117 @@
> +From 71830c804be76cf6abe913ac2fe584947b7a91ea Mon Sep 17 00:00:00 2001
> +From: Samuel Martin <s.martin49@gmail.com>
> +Date: Tue, 24 May 2016 23:08:40 +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.
> +
> +Signed-off-by: Samuel Martin <s.martin49@gmail.com>
> +
> +---
> +changes v1->v2:
> +- use std::atomic_fetch_add_explicit function instead of
> +  __atomic_fetch_add_4;
> +- rework code using cmake_*_check_state and find_library helpers;
> +- quiet-ize checks and clean outputs
> +- extend the commit log
> +---
> + CMakeLists.txt | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
> + 1 file changed, 50 insertions(+)
> +
> +diff --git a/CMakeLists.txt b/CMakeLists.txt
> +index 9dac69f..44f810e 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)
> + 
> ++

Maybe an extra new line here :)

Otherwise:
Reviewed-by: Romain Naour <romain.naour@gmail.com>

Best regards,
Romain

> ++# 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 <atomic>
> ++std::atomic<int> 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)
> +-- 
> +2.8.3
> +
>