ABI matters

Now, upgrading my Gentoo box again. Mainly drived by GCC 4.1.1 upgrade. Upgrade gcc (from 3.4.6 to 4.1.1) means I need to emerge -eav world, but why? ABI involves some knowledge on shared library and some knowledge about linker and loader. The following is GOOD reference

• What's ABI defined by GCC
• HOWTO specificaly discuss this issue (and library in general)
• Book about linker and loader