[cmake-developers] [CMake 0015547]: Changing CMAKE_AR isn't reflected on regenerating build system

[Mantis Bug Tracker]

The following issue has been SUBMITTED. 
====================================================================== 
http://www.cmake.org/Bug/view.php?id=15547 
====================================================================== 
Reported By:                Daniel Schepler
Assigned To:                
====================================================================== 
Project:                    CMake
Issue ID:                   15547
Category:                   CMake
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
====================================================================== 
Date Submitted:             2015-04-29 16:45 PDT
Last Modified:              2015-04-29 16:45 PDT
====================================================================== 
Summary:                    Changing CMAKE_AR isn't reflected on regenerating
build system
Description: 
In 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 Reproduce: 
dschepler at 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 at deb-dschepler:~/scalable-dev/cmake-flto$ mkdir build; cd build
dschepler at 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 at 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 at 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 at 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 Information: 
If 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.
====================================================================== 

Issue History 
Date Modified    Username       Field                    Change               
====================================================================== 
2015-04-29 16:45 Daniel ScheplerNew Issue                                    
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