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List:       flightgear-users
Subject:    Re: [Flightgear-users] Simgear build breaks; SGAtomic.cxx
From:       polly <lister () chathamsurf ! com>
Date:       2009-10-05 16:11:40
Message-ID: op.u1b4lqks9pqgfa () self
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Thank, Curt
  Yes, I had been doing 'make clean' and no yum updates since I was getting  
clean build. I've just now done yum update and
again, 'make clean' and still have the problem> Erik's 10/02 CVS
change was:

	 #if defined(SGATOMIC_USE_GCC4_BUILTINS) && defined(__i386__)	 #if  
!defined(SGATOMIC_USE_GCC4_BUILTINS) && defined (__i386__)

It seems to be a correction, prior to this change the Simgear functions  
were called even if the GCC builtins were supposedly called. It looks like  
after the above CVS change, since I'm on a i686/i386, SGAtomic is  
expecting the GCC builtins to be used. My machine is a non-X64 Athlon, I'm  
not convinced that GCC includes those bultins. Here's an item via google  
"__sync_sub_and_fetch_4 gcc"  :

<<<snip
  Changed 22 months ago by vaclavslavik

*Really* fixed now. Apparently, this is gcc's normal behavior if the  
required primitives aren't supported by the architecture (as is the case  
with i686, unlike x86_64):

Not all operations are supported by all target processors. If a

particular operation cannot be implemented on the target processor, a
warning will be generated and a call an external function will be
generated. The external function will carry the same name as the
builtin, with an additional suffix `_N' where N is the size of the data
type.

Our configure test didn't fail, because it didn't use sync_sub_and_fetch  
return value -- and because int32_t memory access is always atomic on  
i686, the compiler correctly determined this use is supported by target  
architecture -- but wx uses the return value and that's not supported.
end snip >>>>

  .... which suggests to me the tests in SGAtomic.cxx, now that their  
syntax has been changed, are not covering the case of a non x86_64
properly.
Thanks and regards, polly






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