* 生成TAGS文件
find . -name '*.[ch]' -print | etags -
生成TAGS文件
* M - . go to definition
https://www.emacswiki.org/emacs/EmacsTags
* jump back
C-u C-SPC
locally, C-x C-SPC
globally
https://stackoverflow.com/questions/22589339/how-to-jump-back-from-find-tag-in-emacs