MantisBT - CMake
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IDProjectCategoryView StatusDate SubmittedLast Update
0015547CMakeCMakepublic2015-04-29 19:452016-06-10 14:31
ReporterDaniel Schepler 
Assigned ToKitware Robot 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionmoved 
PlatformDebianOSLinuxOS Versionstretch
Product VersionCMake 3.2.2 
Target VersionFixed in Version 
Summary0015547: Changing CMAKE_AR isn't reflected on regenerating build system
DescriptionIn our project, I ran into an issue that switching from non-LTO mode to LTO mode by adding -flto to CMAKE_C_FLAGS_RELEASE, and updating CMAKE_AR and CMAKE_RANLIB to the gcc lto wrappers, isn't successful. On running "make VERBOSE=1", it appears that the Makefiles are still running /usr/bin/ar to generate the intermediate static libraries.
Steps To Reproducedschepler@deb-dschepler:~/scalable-dev/cmake-flto$ tail -n +1 *
==> a.c <==
int a(int n) {
    return n*n + 3;
}

==> CMakeLists.txt <==
cmake_minimum_required(VERSION 3.2)

project(flto)

add_library(a STATIC a.c)
add_executable(main main.c)
target_link_libraries(main a)

==> main.c <==
#include <stdio.h>

int a(int n);

int main() {
    printf("a(5) = %d\n", a(5));
    return 0;
}
dschepler@deb-dschepler:~/scalable-dev/cmake-flto$ mkdir build; cd build
dschepler@deb-dschepler:~/scalable-dev/cmake-flto/build$ CC=gcc-5 cmake -DCMAKE_BUILD_TYPE:STRING=Release ..
-- The C compiler identification is GNU 5.1.1
-- The CXX compiler identification is GNU 4.9.2
-- Check for working C compiler: /usr/bin/gcc-5
-- Check for working C compiler: /usr/bin/gcc-5 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/dschepler/scalable-dev/cmake-flto/build
dschepler@deb-dschepler:~/scalable-dev/cmake-flto/build$ make
Scanning dependencies of target a
[ 50%] Building C object CMakeFiles/a.dir/a.c.o
Linking C static library liba.a
[ 50%] Built target a
Scanning dependencies of target main
[100%] Building C object CMakeFiles/main.dir/main.c.o
Linking C executable main
[100%] Built target main
dschepler@deb-dschepler:~/scalable-dev/cmake-flto/build$ cmake -DCMAKE_AR:PATH=/usr/bin/gcc-ar-5 -DCMAKE_RANLIB:PATH=/usr/bin/gcc-ranlib-5 -DCMAKE_C_FLAGS_RELEASE:STRING="-O3 -DNDEBUG -flto" .
-- Configuring done
-- Generating done
-- Build files have been written to: /home/dschepler/scalable-dev/cmake-flto/build
dschepler@deb-dschepler:~/scalable-dev/cmake-flto/build$ make
[ 50%] Building C object CMakeFiles/a.dir/a.c.o
Linking C static library liba.a
BFD: CMakeFiles/a.dir/a.c.o: plugin needed to handle lto object
BFD: a.c.o: plugin needed to handle lto object
[ 50%] Built target a
[100%] Building C object CMakeFiles/main.dir/main.c.o
Linking C executable main
/tmp/cc9dAt8D.ltrans0.ltrans.o: In function `main':
<artificial>:(.text.startup+0xa): undefined reference to `a'
collect2: error: ld returned 1 exit status
CMakeFiles/main.dir/build.make:86: recipe for target 'main' failed
make[2]: *** [main] Error 1
CMakeFiles/Makefile2:95: recipe for target 'CMakeFiles/main.dir/all' failed
make[1]: *** [CMakeFiles/main.dir/all] Error 2
Makefile:75: recipe for target 'all' failed
make: *** [all] Error 2
Additional InformationIf the first configure includes the CMAKE_AR and CMAKE_RANLIB settings, then the build goes through successfully, and "make VERBOSE=1" shows about what I'd expect. It would be somewhat inconvenient to require completely wiping out the build directory to do the switch, though, as that would lose any other cache settings.
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Issue History
Date ModifiedUsernameFieldChange
2015-04-29 19:45Daniel ScheplerNew Issue
2015-04-30 09:46Brad KingNote Added: 0038654
2016-06-10 14:29Kitware RobotNote Added: 0042769
2016-06-10 14:29Kitware RobotStatusnew => resolved
2016-06-10 14:29Kitware RobotResolutionopen => moved
2016-06-10 14:29Kitware RobotAssigned To => Kitware Robot
2016-06-10 14:31Kitware RobotStatusresolved => closed

Notes
(0038654)
Brad King   
2015-04-30 09:46   
CMAKE_AR is actually stored in "CMakeFiles/${version}/CMake${lang}Compiler.cmake" and is merely initialized by the cache entry of the same name. Some refactoring would be needed to make it changeable later.
(0042769)
Kitware Robot   
2016-06-10 14:29   
Resolving issue as `moved`.

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