Ian Lance Taylor wrote: > John Fine <johnsfine@xxxxxxxxxxx> writes: > >> When an unsigned int is passed or returned in a 64-bit register, does >> either the C or C++ ABI specify that the top half of the register >> contain zero? > > There are threads on the subject at > > http://groups.google.com/group/ia32-abi/browse_thread/thread/f47e0106b21d9269 > > http://gcc.gnu.org/ml/gcc/2008-01/msg00052.html > > Short answer: the ABI does not specify, and gcc's behaviour has > recently changed. That's the 32-bit API, innit? I suppose the 64-bit API, which is the subject of the question, has the same properties. Andrew.
