On 2008-09-22 20:12-0700 Alan W. Irwin wrote:
Now that we have an example of a working ENABLE_LANGUAGE for gfortran, I
agree with your assessment/guess that the CXX and C troubles for that case
are some screw up in one of the C and CXX (but not Fortran) enabling files
in Platform. In fact I am on the track of something
(CMAKE_C_FLAGS_DEBUG_INIT appears not to be initialized for the generic
Linux case and also not for the specific gcc case in Platform) and will
report further later tonight or tomorrow.
The above comment about CMAKE_C_FLAGS_DEBUG_INIT is not correct. Here is
the CMake logic I have traced so far:
According to a note in that file (although this needs to be confirmed by
looking at the source code) CMakeSystemSpecificInformation.cmake is included
by cmGlobalGenerator::EnableLanguage. That file in turn INCLUDEs
CMakeGenericSystem.cmake which in turn INCLUDEs Platform/gcc.cmake which
defines CMAKE_C_FLAGS_DEBUG_INIT for the case of IF(CMAKE_COMPILER_IS_GNUCC)
and CMAKE_CXX_FLAGS_DEBUG_INIT for the case of IF(CMAKE_COMPILER_IS_GNUCXX).
The tests below have been done this time consistently for 2.6.1.
PROJECT(free_eos CXX)
ENABLE_LANGUAGE(C)
==>
CMAKE_CXX_FLAGS_DEBUG:STRING=-g
CMAKE_C_FLAGS_DEBUG:STRING=
i.e., I get the same bad result for 2.6.1 as I did
for 2.6.0 which is not a surprise.
However, if I create the file Platform/Linux-gcc.cmake as a copy
of Platform/gcc.cmake (by analogy with Platform/Linux-GNU-Fortran.cmake)
the same test gives me the good result,
CMAKE_CXX_FLAGS_DEBUG:STRING=-g
CMAKE_C_FLAGS_DEBUG:STRING=-g
Therefore, the above logic that I traced for Platform/gcc.cmake must be
failing somehow (perhaps one or both of CMAKE_COMPILER_IS_GNUCC or
CMAKE_COMPILER_IS_GNUCXX is undefined when CMakeGenericSystem.cmake is
INCLUDEd or one of CMAKE_C_FLAGS_DEBUG_INIT or CMAKE_CXX_FLAGS_DEBUG_INIT
(depending on what language is defined by PROJECT and what language
by ENABLE_LANGUAGE) is set to nothing by subsequent logic).
So it appears that creating the file Platform/Linux-gcc.cmake as a copy of
Platform/gcc.cmake solves the above issue.
However, I then made the mistake of making further experiments for that
case, and I could not get ENABLE_LANGUAGE(CXX) to ever work properly.
For example, if I reverse the above two languages, e.g.,
PROJECT(free_eos C)
ENABLE_LANGUAGE(CXX)
or try either
PROJECT(free_eos NONE)
ENABLE_LANGUAGE(CXX)
ENABLE_LANGUAGE(C)
or
PROJECT(free_eos NONE)
ENABLE_LANGUAGE(C)
ENABLE_LANGUAGE(CXX)
then
==>
CMAKE_CXX_FLAGS_DEBUG:STRING=
CMAKE_C_FLAGS_DEBUG:STRING=-g
i.e., for all three of these patterns C is fine, and C++ is screwed up.
In sum, the above creation of Platform/Linux-gcc.cmake goes through the
identical logic as Platform/gcc.cmake but at a different time (with
variables initialized differently I presume). That subtle change in when
that logic is done apparently solves the ENABLE_LANGUAGE(C) case, but not
the ENABLE_LANGUAGE(CXX) case.
Bill, can you or someone else from Kitware take over now to finish this off?
If you don't have immediate access to Linux, I am willing to do any
experiments you suggest on that platform. Currently, I feel I am
floundering around close to the solution of the problem on my own, but I
think it will require somebody with more comprehensive CMake language
support expertise than mine to determine a really elegant solution for this
Platform bug that works not only for C, but also for CXX in the Linux gcc
case.
By the way, although ENABLE_LANGUAGE(C) works for Linux/gcc with the above
change and ENABLE_LANGUAGE(Fortran) works regardless for Linux/gfortran, the
ENABLE_LANGUAGE(CXX) case is important from the PLplot perspective since our
core library is just C. Thus, when our users enable C++, a set of C++
bindings for that library is created that is analogous to our other optional
language bindings. Right now our users are reasonably happy with our
current CMake-based build system which specifies both C and CXX through our
project statement. Of course, that logic demands they have a C++ compiler,
but that is not too onerous a requirement since C++ compilers are often
installed when a C compiler is installed. However, we did have one complaint
from a user who was stuck with just a C compiler and I would like to
accomodate him (and others in the same category) by making C++ optional as
soon as the ENABLE_LANGUAGE(CXX) case is straightened out for
CMake/Linux/gcc.
Alan
__________________________
Alan W. Irwin
Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).
Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
__________________________
Linux-powered Science
__________________________
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