MantisBT - CMake
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IDProjectCategoryView StatusDate SubmittedLast Update
0014647CMakeCMakepublic2013-12-13 17:112016-06-10 14:31
ReporterSean Patrick Santos 
Assigned ToKitware Robot 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionmoved 
PlatformOSOS Version
Product VersionCMake 2.8.11.1 
Target VersionFixed in Version 
Summary0014647: Inconsistency in the way shared libraries are passed to Fortran vs C linker
DescriptionWhen "target_link_libraries" is called with the full path to a shared file (at least in my case, which is a .so on a Linux system), the behavior is different depending on whether a Fortran or a C compiler is being used for the actual linking step.

For a C compiler, the full path "/usr/lib64/libm.so", gets translated to a simple "-lm" option.

For the Fortran compiler, though, the full path is retained.

In most cases, I haven't even noticed this, because ultimately both end up working. But I've found encountered bugs due to compiler wrappers that behave differently in the two cases. For this reason, I wanted to suggest that this inconsistency should be resolved one way or the other, unless there's a specific reason why the two cases need to be treated differently.
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Issue History
Date ModifiedUsernameFieldChange
2013-12-13 17:11Sean Patrick SantosNew Issue
2013-12-18 11:13Brad KingNote Added: 0034786
2013-12-18 12:56Sean Patrick SantosNote Added: 0034793
2013-12-18 15:10Brad KingNote Added: 0034799
2013-12-18 15:16Sean Patrick SantosNote Added: 0034800
2013-12-18 15:36Brad KingNote Added: 0034802
2013-12-18 15:40Brad KingNote Added: 0034804
2013-12-18 16:04Sean Patrick SantosNote Added: 0034809
2013-12-19 14:18Brad KingNote Added: 0034829
2013-12-19 14:18Brad KingStatusnew => backlog
2016-06-10 14:29Kitware RobotNote Added: 0042447
2016-06-10 14:29Kitware RobotStatusbacklog => 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
(0034786)
Brad King   
2013-12-18 11:13   
As explained here:

 http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/8795/focus=8812 [^]

CMake converts libraries in implicit linker search paths to the "-lm" form.

The difference you see must be due to which directories are detected as implicitly passed to the linker by the compiler front-end. Look under the CMakeFiles/2.8.11.1 directory at the top of the build tree for "CMake*Compiler.cmake" files. Inside there are variables like CMAKE_C_IMPLICIT_LINK_DIRECTORIES. What are they for C and Fortran?
(0034793)
Sean Patrick Santos   
2013-12-18 12:56   
Here are the IMPLICIT_LINK variables for a system where I found the same effect with 2.8.10.2.

This is not the same as the system where I originally found the issue, but this machine has simpler settings. Note that I'm working on HPC systems where these paths can be quite long.

set(CMAKE_C_IMPLICIT_LINK_LIBRARIES "netcdf_c++;netcdff;netcdf;mpi;dl;pthread;rt;c")
set(CMAKE_C_IMPLICIT_LINK_DIRECTORIES "/glade/apps/el6/usr/lib;/glade/apps/el6/usr/lib64;/glade/apps/opt/ncl/6.1.2/gnu/4.4.6/lib;/glade/apps/opt/netcdf/4.3.0/gnu/4.7.2/lib;/opt/ibmhpc/pecurrent/mpich2/gnu/lib64;/glade/u/apps/opt/gnu/4.7.2/lib/gcc/x86_64-unknown-linux-gnu/4.7.2;/glade/u/apps/opt/gnu/4.7.2/lib64;/lib64;/usr/lib64;/glade/u/apps/opt/gnu/4.7.2/lib")

set(CMAKE_Fortran_IMPLICIT_LINK_LIBRARIES "netcdf_c++;netcdff;netcdf;gfortran;m;quadmath;m;c")
set(CMAKE_Fortran_IMPLICIT_LINK_DIRECTORIES "/glade/apps/el6/usr/lib;/glade/apps/el6/usr/lib64;/glade/apps/opt/ncl/6.1.2/gnu/4.4.6/lib;/glade/apps/opt/netcdf/4.3.0/gnu/4.7.2/lib;/glade/u/apps/opt/gnu/4.7.2/lib/gcc/x86_64-unknown-linux-gnu/4.7.2;/glade/u/apps/opt/gnu/4.7.2/lib64;/lib64;/usr/lib64;/glade/u/apps/opt/gnu/4.7.2/lib")


Note that this actually shows up for multiple compilers, and even for a BlueGene system that I've checked, which was why I was inclined to think that there's something that's explicitly treating C and Fortran differently.

But in fact there are differences between some static libraries too, so I was wrong in thinking that this was a shared library issue originally.
(0034799)
Brad King   
2013-12-18 15:10   
Re 0014647:0034793: Both the C and Fortran values you report list "/usr/lib64" so I would expect "/usr/lib64/libm.so" to become "-lm" in both cases. Does the difference occur in the build tree where you got these values?
(0034800)
Sean Patrick Santos   
2013-12-18 15:16   
Yes, they are the same build tree. And in fact I see the same conditions repeating on other systems and with other libraries besides libm.

As far as I can tell, CMAKE_Fortran_IMPLICIT_LINK_DIRECTORIES does not cause *any* absolute library paths to be converted to "-l" options when linking with the Fortran compiler, at least in CMake 2.8.10 and 2.8.11. So maybe that is the real bug here.
(0034802)
Brad King   
2013-12-18 15:36   
It looks like conversion never occurs for Fortran. The conversion takes place in cmComputeLinkInformation::CheckImplicitDirItem here:

 http://cmake.org/gitweb?p=cmake.git;a=blob;f=Source/cmComputeLinkInformation.cxx;hb=v2.8.12.1#l1176 [^]

but only if LinkTypeEnabled is true. That is set here:

 http://cmake.org/gitweb?p=cmake.git;a=blob;f=Source/cmComputeLinkInformation.cxx;hb=v2.8.12.1#l808 [^]

by looking up the CMAKE_${type}_LINK_DYNAMIC_${lang}_FLAGS value for the current target type and linker language. Those values are set in the Modules/Platform/*.cmake files for C. For CXX they are copied from C here:

 http://cmake.org/gitweb?p=cmake.git;a=blob;f=Modules/CMakeCXXInformation.cmake;hb=v2.8.12.1#l184 [^]

There is no equivalent in Modules/CMakeFortranInformation.cmake, and that bug propagates back through all the above steps to result in not converting library linking in implicit directories.
(0034804)
Brad King   
2013-12-18 15:40   
To test my hypothesis in 0014647:0034802, add this to your project code:

 foreach(type SHARED_LIBRARY SHARED_MODULE EXE)
  set(CMAKE_${type}_LINK_STATIC_Fortran_FLAGS "-Wl,-Bstatic")
  set(CMAKE_${type}_LINK_DYNAMIC_Fortran_FLAGS "-Wl,-Bdynamic")
 endforeach()

(with whatever are the proper flags). Does it make Fortran linking use the "-lm" form?
(0034809)
Sean Patrick Santos   
2013-12-18 16:04   
Yes, that did the trick.
(0034829)
Brad King   
2013-12-19 14:18   
Unfortunately I think there are several Fortran compilers that do not recognize the same options their C compiler uses (like -Wl,-Bstatic) for specifying the library search path. The flag mapping for this language will have to be added to the information file for each compiler/platform combo.

Moving to backlog for now.
(0042447)
Kitware Robot   
2016-06-10 14:29   
Resolving issue as `moved`.

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