引用:!!! Multiple versions within a single package slot have been
!!! pulled into the dependency graph:
dev-libs/xerces-c:
('binary', '/', 'dev-libs/xerces-c-2.7.0-r1', 'merge') pulled in by
('binary', '/', 'dev-libs/xalan-c-1.10.0', 'merge')
('binary', '/', 'dev-libs/xerces-c-2.8.0', 'merge') pulled in by
('binary', '/', 'app-emulation/virtualbox-1.5.6', 'merge')
后来是在gentoo bug下看到了解决方法的：
dev-libs/xerces-c -icu
写进 /etc/portage/packages.use 里面
>=dev-libs/xerces-c-2.8.0
写进
/etc/portage/package.mask
这样就可以解决多个版本软件同时使用的问题。