On Thu, Oct 25, 2007 at 11:25:52AM -0400, Daniel Jacobowitz wrote: > On Wed, Oct 24, 2007 at 03:06:42PM -0700, Joe Buck wrote: > > But the way that the object is passed in this case, and the stack layout, > > are completely defined on any platform that obeys the cross-platform API > > you will find at > > > > http://www.codesourcery.com/cxx-abi/ > > > > and this definition specifies that everything will look exactly the same > > as if it were a POD with the same members declared in the same order. > > I don't think that's true. I believe the non-POD must be passed in > memory, but GCC would be permitted to pass the POD in a register if it > preferred. The layout is defined by the C++ ABI, but not the argument > passing conventions.
One of the purposes of the C++ ABI is to allow different compilers to interoperate. The freedom you describe would prevent gcc-compiled code from behaving correctly with icc-compiled code, for example. So yes, argument passing conventions are part of the ABI. Now, in this case there is an "out": a compiler developer can argue that passing a non-pod to a variadic function isn't defined, so the ABI doesn't matter.
