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Re: Absolute paths generated by libtool.

From: Christopher Hulbert
Subject: Re: Absolute paths generated by libtool.
Date: Tue, 14 Nov 2006 14:17:42 -0500

On 11/14/06, Benoit Sigoure <address@hidden> wrote:
Hello folks.

I'm developing Qt-based applications. The build system is controlled by the
autotools rather than by Qmake.

I'm porting our projects on Windows. We're using an automated build system
( to build every commit on Linux/OSX/Windows. Automating the
process on Windows proved to be really annoying. I looked at how other
projects do it (Python, KDE, Subversion etc.) they all seem to use hand
written .bat files and/or (for Visual C++) with nmake and co. I
didn't want to deal with special Makefiles or setting up a special build
system for each project, so I tried to do something more generic.

Things are rather complicated but I'll try to explain them here. Everything
might not be relevant to the problem described below but I suppose you people
have a good experience about porting applications so you might be able to
advise me.

First off, I chose to use a Cygwin environment for the buildfarm. This was
convenient since Cygwin comes with lots of packages (python, vim, zsh etc)
and make it easy to have a complete environment on the Windows machine. The
buildbot (which is a python app) runs in that environment.

Qt distributes Windows binaries for mingw only so I ended up installing
mingw. This entails that everything is built by the mingw-gcc toolchain rather
than by the cygwin-gcc. Anyway, I *guess* that building mingw apps in a
Cygwin environment isn't a problem since there is probably not much
differences between both.

You can compile in mingw mode by using the "-mno-cygwin" flag to cygwin gcc.

However, doing this made me run into several problems. For instance, Qt
generates Makefiles that have rules such as:
C:\Foo\Bar: C:\Baz\Qux
Which is a problem for cygwin's GNU make (since it sees "C" as a target). For
some reason the mingw GNU make has no problem with this kind of rule, I guess
they patched it. Nevermind, let's use mingw GNU make. The problem is that
when make runs commands such as C:\Qt\4.2.1\bin\moc.exe, the backslashes are
interpreted by the shell (cygwin's shell) which leads to the execution of the
command C:Qt4.2.1binmoc.exe. I tried to use MSYS's shell (the shell provided
with mingw) or cmd.exe directly but this wouldn't work (for some reason it
always ended up running C:Qt4.2.1binmoc.exe).

I ran into this recently with the latest cygwin make 3.81. The move
from 3.80 to 3.81 dropped support for dos style paths. here is a link
to a patch which worked for me. Note that you need to install the
source for make which ends up in /usr/src.

And here's an example after compiling.

-bash-3.2$ cat Makefile
c:\cygwin\home\chulbert\test.exe: c:\cygwin\home\chulbert\test.c
       gcc -mno-cygwin test.c
-bash-3.2$ cat test.c
#include <stdlib.h>
#include <stdio.h>

   return EXIT_SUCCESS;
-bash-3.2$ make
gcc -mno-cygwin test.c

My idea was to write a perl script and to invoke make That
script would rewrite the command properly so that it works within the Cygwin
environment. I succeeded and I can now run configure scripts and compile my
projects using that shell-wrapper.
In order to make this automatic and transparent, I have ~/bin first in my
PATH and I wrote a shell script named make.exe there that forwards the
invocation of make to mingw's GNU make with the SHELL variable set.

Hopefully you can get rid of all this if you use the patched make?

However, on last problem remains, and that's where libtool comes in. MingW
applications don't know anything about the cygwin environment, they're not
aware of the pseudo filesystem emulated by cygwin. At the end of the
compilation, libtool is invoked to link the final executable but for some
reason, it transforms a relative path in an absolute one:

*snip link*
No such file or directory

Make sure to specify prefix and exec-prefix in the form
"c:/path/for/install". This is what libtool puts in the .la (I think).

* snip other question, etc *

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