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List: python-patches
Subject: [Patches] [ python-Patches-1324762 ] Compiling and linking main()
From: noreply () sourceforge ! net (SourceForge ! net)
Date: 2005-11-30 18:07:41
Message-ID: E1EhWMn-0002eF-TX () sc8-sf-web1 ! sourceforge ! net
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Patches item #1324762, was opened at 2005-10-12 13:45
Message generated for change (Comment added) made by cludwig
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Category: Build
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Submitted By: Christoph Ludwig (cludwig)
Assigned to: Nobody/Anonymous (nobody)
Summary: Compiling and linking main() with C++ compiler
Initial Comment:
The attached patch proposes a resolution to the discussion
started in
<url:http://thread.gmane.org/gmane.comp.python.devel/69651>
regarding the compiler (C vs. C++) used to compile python's
main() and to link the executable.
The patch contains the following changes:
1) The configure option --with-cxx is renamed
--with-cxx-main. This was done to avoid surprising the user
by the changed meaning. Furthermore, it is now possible
that CXX has a different value than provided by
--with-cxx-main, so the old name would have been
confusing.
2) The compiler used to translate python's main() function is
stored in the configure / Makefile variable MAINCC. By
default, MAINCC=$(CC). If --with-cxx-main is given (without
an appended compiler name), then MAINCC=$(CXX). If
--with-cxx-main=<compiler> is on the configure command
line, then MAINCC=<compiler>. Additionally, configure sets
CXX=<compiler> unless CXX was already set on the
configure command line.
3) The command used to link the python executable is (as
before) stored in LINKCC. By default, LINKCC='$(PURIFY)
$(MAINCC)', i.e. the linker front-end is the compiler used to
translate main(). If necessary, LINKCC can be set on the
configure command line in which case it won't be altered.
4) If CXX is not set by the user (on the command line or via
--with-cxx-main), then configure tries several likely C++
compiler names. CXX is assigned the first name that refers
to a callable program in the system. (CXX is set even if
python is built with a C compiler only, so distutils can build
C++ extensions.)
5) Modules/ccpython.cc is no longer used and can be
removed.
----------------------------------------------------------------------
>Comment By: Christoph Ludwig (cludwig)
Date: 2005-11-30 19:07
Message:
Logged In: YES
user_id=1266029
My second patch was indeed broken since it referred to $CC
before the call to AC_PROG_CC in configure.in. That caused
CC=gcc and CXX=c++ if neither --with-cxx-main nor CC was
given on the command line.
I am going to upload a third version (cxx-main.patch3) that
fixes this problem by moving the code that evaluates
--with-cxx-main below AC_PROG_CC.
To repeat what I wrote in my last comment: This patch does
not address the issue that distutils calls $CC in order to
compile C++ source files and calls $CXX in the linking step
only. Howevr, the patch tries to ensure that CXX is always
set to a sensible value in the Makefile - even if Python is
built exclusively with $CC. Thus, distutils has a fighting
chance to do the right thing (whatever that is) when
building C++ extensions since it uses the value of CXX
found in Python's Makefile.
----------------------------------------------------------------------
Comment By: Christoph Ludwig (cludwig)
Date: 2005-11-25 11:51
Message:
Logged In: YES
user_id=1266029
distutils behaves the same way in Python 2.4.1, as I
mentioned
<url:http://article.gmane.org/gmane.comp.python.devel/69817>.
My patch does not address this problem at all. (It should
be fixed in distutils, but I did not the time to look into
it yet.)
I am surprised that, on your machine, CC=gcc and CXX=c++. I
will look into this next week.
----------------------------------------------------------------------
Comment By: Jack Jansen (jackjansen)
Date: 2005-11-25 00:26
Message:
Logged In: YES
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Well, as I commented on this patch and you quickly followed my suggestions I
felt obliged to test your fix, but I'm not sure about the outcome.
I built a C++ extension on MacOSX 10.4, gcc 4, framework Python. The good
news is that it worked fine, everything built and worked as before. BUT: both
with and without your mods my C++ modules are compiled with "gcc", not "g
++" or "c++". Linking is done with "c++", in both cases. I looked at distutils
and it seems that it could indeed be the case that CXX is only used for linking
and never for compilation, but I'm not 100% sure.
Additionally, the Makefile has
CC= gcc
CXX= c++
which is technically fine on my machine (g++ == c++), but may not work
always.
Maybe someone who has a machine with both cc/c++ and gcc/g++ installed,
and preferrably incompatible compilers, could give this patch a try too?
----------------------------------------------------------------------
Comment By: Christoph Ludwig (cludwig)
Date: 2005-11-10 19:42
Message:
Logged In: YES
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I am going to upload a revision of my patch that addresses
jackjansen's comment: It sets CXX to g++ or c++ if CC is gcc or
cc, respectively. Additionally, it writes a warning if configure had to
"guess" the C++ compiler and tells the user how to override this
guess.
The change is in lin with jackjansen's second suggestion. It is
pretty straight forward and avoids fragile configure magic.
----------------------------------------------------------------------
Comment By: Jack Jansen (jackjansen)
Date: 2005-11-08 23:51
Message:
Logged In: YES
user_id=45365
One question: is step 4 a wise idea? Picking a random C++ compiler if
multiple are available may result in picking a vendor C++ when the user
has specified CC=gcc, for example.
OTOH, actually doing the configure magic to determine that the selected
C++ works together with the c-compiler selected for Python may be
overkill too.
Maybe try only standard combinations cc/c++ gcc/g++ and otherwise
require --with{out}-cxx?
----------------------------------------------------------------------
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