Re: [Qemu-devel] [PATCH] configure: disallow ccache during compile tests

[John Snow <jsnow@redhat.com>]

On 10/29/2015 02:17 AM, Markus Armbruster wrote:
> John Snow <jsnow@redhat.com> writes:
> 
>> If the user is using CCACHE during the configuration step,
>> it may interfere with some of the configuration tests,
>> particularly the "Is CCACHE interfering with macro analysis" step,
>> which is a bit of a poetic problem.
>>
>> 1) Disallow CCACHE from reading from the cache during configure,
>>    but don't disable it to allow us to see if it causes other problems.
> 
> This is confusing.  "don't disable it entirely"?
> 

We allow it to submit items into the cache, but not to read items from
the cache. This prevents it from picking up cached results to the
compile tests.

I don't disable it entirely (just pass-through to the real compiler
without using ccache at all) because I still want to allow ccache to be
processing things to test for ccache failures -- particularly the ccache
macro check that occurs later.

If I just disable ccache, that later check is meaningless. Setting the
cache to "write only" gives me the best of both worlds.

>> 2) Force off CCACHE_CPP2 during the ccache test to get a deterministic
>>    answer over whether or not we need to enable that feature later.
>>
>> Signed-off-by: John Snow <jsnow@redhat.com>