Re: A flaw in dep generation with gcc -MMD?

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Nov 18, 2011, 21:16 UTC
Message-ID: <20111118211645.GA27440@elie.hsd1.il.comcast.net>
In-Reply-To: <loom.20111118T191851-152@post.gmane.org>

Hi,

(restoring cc list.  Unfortunately gmane's web interface doesn't
 provide a built-in way to reply-to-all.  [1] has a hackish
 workaround.)
Samuel Bronson wrote:

> Nguyen Thai Ngoc Duy writes:

Show 5 quoted lines

>> "gcc -MF depfile -MMD -MP -c -o path/to/file.o" will produce "depfile"
>> with target given by "-o". When ccache runs, it executes "gcc -MF
>> depfile -MMD -MP -E" instead to get the final content for hashing.
>> Notice that "-c -o" combination is replaced by "-E". The latter
>> produces target without leading path.

[...]

> I'm pretty sure you should report this against ccache; GCC seems to be
> behaving as documented.

Seems to have been fixed by v3.0pre0~187:

 commit e8354384
 Author: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
 Date:   Sun Nov 1 19:39:58 2009 +0100

     Fix handling of the -MD and -MDD options

     From <http://lists.samba.org/archive/ccache/2007q2/000272.html>:

     The -MD and -MDD options automatically determine where the dependency file
     should land and what the target should look like based on the -o option.
     However, ccache drops -o and things mess up. The original patch was posted by
     Kaz Kylheku but I reworked it to make it work properly. Here is his post:

     http://lists.samba.org/archive/ccache/2006q4/000249.html

Workaround incoming in a few moments.

Thanks, Jonathan