OK, here is a problem. I wanted to play a little bit with uploadprogress PECL extension. Normally installation of PECL extension is very easy, you just do
$sudo ./bin/pecl install uploadprogress
form console and PECL installer would do the rest, which was my case also - extension was downloaded from Internet and compiled successfully. After adding extension="uploadprogress.so" to php.ini and restarting XAMPP I've got next error
$ sudo ./lampp restartapache
XAMPP: Stopping Apache with SSL...
Warning: PHP Startup: Unable to load dynamic library '/opt/lampp/lib/php/extensions/no-debug-non-zts-20090626/uploadprogress.so' - /opt/lampp/lib/php/extensions/no-debug-non-zts-20090626/uploadprogress.so: wrong ELF class: ELFCLASS64 in Unknown on line 0
Running file on uploadprogress.so confirmed that system compiled 64bit version of library
$ file lib/php/extensions/no-debug-non-zts-20090626/uploadprogress.so
lib/php/extensions/no-debug-non-zts-20090626/uploadprogress.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, not stripped
When you sit back and think for a moment, this is actually OK because I am running 64bit version of Kubuntu and 32bit version of XAMPP (there is no 64bit version of XAMPP for now) for my development environment, so my C compiler and linker are 64bit and will produce 64bit libraries.
Here is a solution for this situation.
First you need to add 32bit libraries for compilation, for example on ubuntu systems this would look like
$sudo apt-get install g++-multilib
Then you need to manually download PHP PECL extension that you want
$tar xzf uploadprogress-1.0.1.tgz
Now if you have multiple PHP installed, like I do, you need to tell in console which one you want to use currently. I for example have /usr/bin/php installed from my package manager, but my main php is in my XAMPP which is on /opt/lampp/bin path. So first you need to find out which php you are currently using in console
Now we are ready to compile and link our PHP extension
$CFLAGS=-m32 CPPFLAGS=-m32 CCASFLAGS=-m32 ./configure
This m32 flags are telling compiler to create 32bit extension. All we have to do now is to copy our new extension to current XAMPP PHP extension directory
$cp modules/uploadprogress.so /path_to_ext_lib
And then add "extension=uploadprogress.so" to our php.ini.
That's it, we now have 32bit version of uploadprogress.so PHP extension which is compatible with our XAMPP installation.
If you are getting following error when trying to restart apache or when you start php from command line
Warning: PHP Startup: uploadprogress: Unable to initialize module
Module compiled with module API=20060613
PHP compiled with module API=20090626
These options need to match
That actually means that you have compiled PECL extension against wrong PHP header files - which was exactly the error I have done. I upgraded XAMPP couple of times in the past, but didn't refresh development packages. Downloading latest development package from http://www.apachefriends.org/download.php?xampp-linux-devel-1.7.4.tar.gz and updating my XAMPP installation fixed this - of course you need to recompile extension again.