From mboxrd@z Thu Jan  1 00:00:00 1970
From: Samuel Bronson <naesten@gmail.com>
Subject: Re: A flaw in dep generation with gcc -MMD?
Date: Fri, 18 Nov 2011 18:30:05 +0000 (UTC)
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References: <CACsJy8BZMDyf4MCiKxPJ5Z+XS+C-MC82SpMFyWgiXmb9xCnScw@mail.gmail.com> <20111118034142.GA25228@elie.hsd1.il.comcast.net> <CACsJy8A44PFtYrm8NQU+48sVkOe8mjJyO9opO5-TwRtAd-TKsQ@mail.gmail.com> <buor516m3w7.fsf@dhlpc061.dev.necel.com> <CACsJy8BuCdT3rRjc5u6Ex5RRgSbL_0SFF0GW-dTGqet4sG2cwg@mail.gmail.com> <CACsJy8CKmjq01KoLRzOnnaf6RwFCQJfjxziqKTZW9HDyd8CagA@mail.gmail.com>
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Nguyen Thai Ngoc Duy <pclouds <at> gmail.com> writes:

> 
> On Fri, Nov 18, 2011 at 6:34 PM, Nguyen Thai Ngoc Duy <pclouds <at> gmail.com> 
wrote:
> > OK it's not gcc problem. I upgraded to 4.5.3 and still had the same
> > problem. I used ccache though. Without ccache, gcc produced correct
> > .o.d files.
> 
> "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.
> 
> Not sure if I should report this to ccache or gcc. In the meantime,
> may be we should recognize the situation and switch off
> COMPUTE_HEADER_DEPENDENCIES when ccache is used (maybe hard).

I'm pretty sure you should report this against ccache; GCC seems to be
behaving as documented. (I believe there is another flag that ccache
should be passing in to tell GCC what target to use in the depfile.)

Of course, it'd be wise to make sure that this problem still occurs in
the most recent version of ccache you can conveniently try it with before
reporting...