Some time ago you provided a HowTo get the 64 bits compile & run time environment for Knoppix 7.0.2
Hi Gilles!

Under Knoppix 7.6.0 I did the following to run 'Three Million Digits PI Calculation'.
I booted Knoppix 7.6.0 with 64 bit kernel in VirtualBox 5.0.10 on a MS Windows 8.1 host. I used a virtual machine with 2 cores and 3072 MB of RAM.

In an LXTerminal I did some preparing steps.
Code:
sudo apt-get update
sudo apt-get install time
sudo apt-get -t testing install libc6-dev-amd64
mkdir /home/knoppix/src
cd /home/knoppix/src
wget http://h2np.net/pi/pi_quick_start.tar.gz
tar xf pi_quick_start.tar.gz
cd pi_quick_start
export CFLAGS=-m64
I loaded start.sh into a text editor and replaced all occurences of 'cc ' with 'gcc -m64 '. I saved the file and closed the text editor.
I issued
Code:
./start.sh
and answered all questions with 'y'. I got the following result.
Start and wait for a while...done
Command being timed: "./pi 3000000"
User time (seconds): 2.06
System time (seconds): 0.09
Percent of CPU this job got: 99%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:02.16
Type any key for finish
The command 'file pi' gave
pi: ELF 64-bit LSB executable, x86-64, version 1 (GNU/Linux), statically linked, for GNU/Linux 2.6.32, BuildID[sha1]=88fc7ab989da115e5771ec97aefe8d964726a127, not stripped
Btw. I am _not_ the inventor of Knoppix.

Best Regards.