Hi, On 01/30/2013 02:18 PM, Michael Matz wrote:
> On Wed, 30 Jan 2013, Andrew Haley wrote: > >> I'm looking at Section 3.2.3, Parameter Passing. >> http://artfiles.org/kernel.org/pub/scm/devel/binutils/hjl/x86-64-psabi.git/ >> >> I still cannot tell whether parameters should or should not be sign- or >> zero-extended when they are moved into registers at a call. I'm guessing >> not. > > It's intentionally unspecified. Aha! It would have been nice if the psABI said so explicitly. Quite a few people have spent time trying to find this information. >> Which is it? This is important for interworking. > > How? You aren't allowed to access the bits outside the specified argument > type (which must match on caller and callee side), so you can't observe > them, so it's not required to specify their content. OK, thanks. It's clear now. The problem is that LLVM assumes that values are extended at a call. GCC does that, but libffi doesn't. So, calls via libffi to LLVM don't work correctly. Andrew.
