[ccache] direct mode

[Joel Rosdahl]

> Perhaps a rename is needed as the title implies it is ubuntu specific and
intermittant?

Yes, done.

-- Joel


On 18 October 2013 12:22, Ian Norton <inorton at gmail.com> wrote:

> I've updated https://bugzilla.samba.org/show_bug.cgi?id=8424.
>
> Perhaps a rename is needed as the title implies it is ubuntu specific
> and intermittant?
>
> On 18 October 2013 11:05, Ian Norton <inorton at gmail.com> wrote:
> > Ok. I should have tried it before hand.  ccache *doesnt't* notice the
> > addition of the new header and still gives me a .o file from the first
> > invocation.
> >
> > bug?
> >
> > On 18 October 2013 10:54, Ian Norton <inorton at gmail.com> wrote:
> >> Hello All,
> >>
> >> I have a question about direct mode, it follows on from an old thread
> >> I've seen in the archives:
> >>
> >> http://www.mail-archive.com/ccache@lists.samba.org/msg00150.html
> >>
> >> I'll quote inline and follow on.
> >>
> >> Joel Rosdahl wrote:
> >>> tridge wrote:
> >>> > Also, does the hashtable used for included_files preserve the
> >>> > ordering? (the order of includes is also vital). Or do you rely on
> the
> >>> > hash of the file that does the #include changing for that?
> >>
> >>> The hashtable is unordered, and yes, I rely on the hash of the input
> >>> file to keep track of the ordering, and also of course on the include
> >>> file hashes. For a given manifest, the source file (and therefore the
> >>> order of the first level of include files) is known since the manifest
> >>> is looked up given the hash of the input file (and some more
> >>> information), and all other levels of include files are taken
> >>> care of using the same kind of reasoning. In other words, if the
> >>> include file order changes in some file, then the hash of that file
> >>> changes too, which leads to a cache miss. Which include files the
> >>> preprocessor reads is of course also a function of compiler options
> >>> like -I, but that is handled by also hashing those options when
> >>> computing the hash in direct mode. Do you see any potential problem
> >>> here?
> >>
> >> I realise I'm probably missing something, but how does direct mode
> >> handle the case where
> >> the command line args have not changed, and nor have the source file
> >> or previously used headers *but* a header file has been added to a
> >> folder on one of the -I paths? eg:
> >>
> >> hello.c:
> >> #include "test.h"
> >>
> >> inc1/test.h:
> >> void hello(void);
> >>
> >> gcc -I inc2 -I inc1 -c hello.c
> >>
> >> later, someone makes a new file:
> >>
> >> inc2/test.h:
> >> int hello(void);
> >>
> >> The same command line and original inputs would result in a different
> file.
> >>
> >> How does direct mode cover this case ( all our common input data has
> >> not changed )
> >>
> >> Many Thanks, ccache is fantastic btw!
> >>
> >> Ian
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