This is a good example why that's good idea to check bug reports or forums before emerge/upgrade big package (long build time or long list of upgrading dependencies).

I had been holding up on libreoffice since version 3.3.4, the next stable version 3.4.x which I masked because it has long dependencies list which was required by 3.3.4. But yesterday, I decided to upgrade libreoffice to 3.4.5.2 even the dependencies list is still long.

Almost 20 packages were new installs on my system and I have to have CUPS and gstreamer and all other sorts I don't use. Merging from the source is too overwhelming for me. The last version I built was openoffice-3.0.0, 3 hours, 30 minutes and 12 seconds.

After finished, I did not run it right away and I just knew it has a bug report (and a thread) which you will see this error message:
~ $ loffice 
/usr/bin/loffice: line 2: 29884 Illegal instruction     /usr/lib64/libreoffice/program/soffice "$@"

Apparently, it only affects AMD64 arch and I am using that.

For now, I am uncommenting this line in /etc/portage/packages.mask:
=app-office/libreoffice-bin-3.4.5.2

and re-emerging for downgrading. Shouldn't have commented out that line. ;)