Re: ABI compatibility regression: Return values on x86

["H.J. Lu" <hjl@lucon.org>]

On Tue, Jan 08, 2008 at 01:57:50PM +0000, Andrew Haley wrote:
> H.J. Lu writes:
>  > On Mon, Jan 07, 2008 at 06:32:08PM +0000, Andrew Haley wrote:
>  > > 
>  > > So, what now?  Can we even agree about what the psABI actually says
>  > > about sign-extending result values?  Was what we did before correct,
>  > > or what we do now?  I don't believe that it doesn't matter.
>  > 
>  > You can follow up with this thread in ia32 psABI discussion group:
>  > 
>  > http://groups.google.com/group/ia32-abi/browse_thread/thread/f47e0106b21d9269
> 
> Thanks for the reference.  The attitude there looks surprisingly
> complacent, but if Intel and gcc x86 maintainers agree that it doesn't
> matter I suppose I'll have to defer to the weight of opinion.
> 

My understanding is either way is ia32 psABI compliant. If the
caller code generated by gcc is ia32 psABI compliant, that is

---
callers need to assume that return value is in %al/%ax and that
the upper bits of %eax are undefined.  If the caller needs a 32-bit
sign- or zero-extended value, it needs to do the extend itself.
---

it shouldn't be a problem.


H.J.