[CMake] Properly Detecting Win64

[David Cole]

On Tue, Apr 19, 2011 at 5:44 PM, James Bigler <jamesbigler at gmail.com> wrote:

> On Tue, Apr 12, 2011 at 2:24 PM, Bill Hoffman <bill.hoffman at kitware.com>wrote:
>
>> On 4/12/2011 4:13 PM, David Cole wrote:
>>
>>  Does somebody have reproducible steps to get to the point where
>>> CMAKE_SIZEOF_VOID_P disappears??
>>>
>>> I've never seen that...
>>>
>>> How many times do you have to re-configure before you start seeing this
>>> behavior? That sounds like something is just really wrong somewhere, and
>>> it would be a good thing to track down exactly what that is.
>>>
>>>  This variable is stored in this file:
>>
>> CMakeFiles/CMakeCCompiler.cmake
>>
>> It should not go away.
>>
>> -Bill
>>
>>
>>
> I just had this happen to one of my colleagues with a fresh build
> directory.  When I looked into CMakeCCompiler.cmake this is what I found:
>
> # Save compiler ABI information.
> SET(CMAKE_C_SIZEOF_DATA_PTR "")
> SET(CMAKE_C_COMPILER_ABI "")
>
> IF(CMAKE_C_SIZEOF_DATA_PTR)
>   SET(CMAKE_SIZEOF_VOID_P "${CMAKE_C_SIZEOF_DATA_PTR}")
> ENDIF(CMAKE_C_SIZEOF_DATA_PTR)
>
> For whatever reason CMAKE_C_SIZEOF_DATA_PTR is empty.
>
> What could cause this to happen?  Is there perhaps a race condition or some
> other failure when CMake detects this value?
>
> James
>
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If it is a race condition that simply occurs "sometimes, sproadically" then
we should be able to reproduce this by writing a script that tries to
configure a project over and over again into a clean directory.

But I'm not convinced it's as simple as that. There must be something
happening (or some condition on certain machines/platforms/compilers) that
triggers it... otherwise, we'd see this on the CMake dashboard results
sometimes, wouldn't we?

What compiler/generator are you using in this instance?
Does it repeat with a fresh build directory on this project in this
environment? Or does it go away with a new fresh build?

Is the project that demonstrates this behavior public? (Can I try it
here...?)

Thanks,
David
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