(require 'xref)
(defun my-c-hook ()
  (interactive)
  (require 'gxref)
  (add-to-list 'xref-backend-functions 'gxref-xref-backend)

  ;; always let gxref figure out the root dir, dont reuse global one
  (setq-local gxref-project-root-dir nil)
  (let ((path (buffer-file-name)))
    (when path
      (setq path (expand-file-name path))
      (when (string-match-p (rx "/linux") path)
	(c-set-style "linux"))))

  ;; if the file doesnt have trailing whitespace, keep it this way
  (when (not (buffer-has-trailing-whitespace))
    (add-hook 'before-save-hook 'delete-trailing-whitespace)))
(add-hook 'c-mode-hook 'my-c-hook)