hi, everyone.
i am just a newbie here. i have a question. can anyone do me a favour figuring it out for me?

it is HOW TO CONSTRUCT A TOOLCHAIN?
for example, if gcc needs to be modified, then why? and how? and which part should be modified?
and anything that have relationship with this subject.

i will be appreciated too, if anyone can tell me , such as you can read such articles, you can go to such websites, and so on.