From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f67.google.com ([74.125.82.67]:35333 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751124AbcEWXC2 (ORCPT ); Mon, 23 May 2016 19:02:28 -0400 Received: by mail-wm0-f67.google.com with SMTP id f75so847988wmf.2 for ; Mon, 23 May 2016 16:02:28 -0700 (PDT) From: Kieran Bingham Subject: Automatic dependency resolution on generated python file Message-ID: <57438C01.6090601@bingham.xyz> Date: Tue, 24 May 2016 00:02:25 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: linux-kbuild@vger.kernel.org, Michal Marek Cc: Jan Kiszka Hi Kbuild / Michal, I've been working through a problem that Jan has reported whereby if we modify a file included by our template for constants.py, the generated file is not rebuilt. The rule/cmd [0] to generate the python constants is cmd_gen_constants_py which uses the $(CPP) with $(c_flags) to create the output. One benefit of this is that it already creates the $(depfile) through the addition of the flags provided by $(c_flags), however as yet it would seem that my efforts to understand how the $(depfile) gets included have failed. >From what I can tell, the $(call if_changed...) rule is generating my targets .constants.py.cmd, but the .d file is not being utilised. By swapping $(call if_changed, ) to $(call if_changed_dep,...) I can see that my .constants.py.cmd [1] file now has (apparently) correct dependency rules being generated. However they still don't take actual effect. If I 'touch/modify' one of the files I have added to the #includes, then my target is not rebuilt (I have added include/linux/kieran.h for testing this specifically without rebuilding all other objects) I can see at the bottom of my .constants.py.cmd : scripts/gdb/linux/constants.py: $(deps_scripts/gdb/linux/constants.py) $(deps_scripts/gdb/linux/constants.py): which looks like it's doing the right thing to me ... except it's not actually allowing the rule to run if a dependency is updated. Is this failing because it is being called from the top Kbuild, as part of making sure it is built after bounds.h, or is it because I'm not generating from the builtin rules? I'm hoping perhaps I've missed a stage or something obvious that will make this automatic dependency resolution 'just-work' for recreating the constants file. -- Regards Kieran Bingham [0] https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/scripts/gdb/linux/Makefile [1] http://paste.ubuntu.com/16645481/