[ccache] ccache false cache hit when creating precompiled headers

[Joel Rosdahl]

> This doesn't fix the original bug report. As far as I can see the fix is
> in the area of USING precompiled headers not CREATING them.

Ah, I see.

> Can you re-open the original bug or should I create a new one?

I'll reopen it and look into a better fix. Thanks!

-- Joel



On 12 August 2014 21:59, Mark Fieldhouse <mark at mediasolutions.co.uk> wrote:

> Hi Joel,
>
> This doesn't fix the original bug report. As far as I can see the fix is
> in the area of USING precompiled headers not CREATING them.
> Can you re-open the original bug or should I create a new one?
> I have a brute force fix that stops ccache from caching precompiled
> headers all together.
> But you could probably come up with a better fix.
> I can show you simply how to reproduce the problem in a few lines.
> In testing I used the tip version of ccache on the master branch.
>
> Regards,
>
> Mark
>
> -----Original Message-----
> From: joel.rosdahl at gmail.com [mailto:joel.rosdahl at gmail.com] On Behalf
> Of Joel Rosdahl
> Sent: 08 August 2014 09:37
> To: Mark Fieldhouse
> Cc: ccache list
> Subject: Re: [ccache] ccache false cache hit when creating precompiled
> headers
>
> Hi Mark,
>
> See https://bugzilla.samba.org/show_bug.cgi?id=10212.
>
> -- Joel
>
> On 4 August 2014 22:09, Mark Fieldhouse <mark at mediasolutions.co.uk>
> wrote:
> Hello,
>
> ccache appears to break our compilation by incorrectly retrieving cached
> precompiled headers.
>
> The problem is our build has a header file which has;
>
> #define NUM_COMPOSITE_OUTPUTS 0
> void func(int x);
>
> This gets compiled and put in the cache by ccache.
> We then change the file to be;
>
> #define NUM_COMPOSITE_OUTPUTS 2
> void func(int x);
>
> And ccache runs its own 'direct' hash function and correctly decides
> that the file is not in the cache.
> Then it runs the C pre-processor and hashes the output.
>
> The output of the C pre-processor hasn't changed so ccache incorrectly
> retrieves the cached version of the file
> Which has;
> #define NUM_COMPOSITE_OUTPUTS 0
>
> Failed build.
>
> Let me know if this is a known issue or if you'd like me to raise a bug
> report?
>
> Cheers,
> Mark
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