Re: Extract the return value in finish_command on Xtensa.

[Andrew Cagney <cagney@gnu.org>]

> On Wed, Jul 14, 2004 at 03:38:34PM -0400, Andrew Cagney wrote:
> 
>>>> >I am working on a port of GDB to the Xtensa architecture.
>>>> >
>>>> >Unfortunately, it is impossible on Xtensa to extract the return value once 
>>>> >the 'callee' has returned to the 'caller' without analyzing the call 
>>>> >instruction (if there was one). Depending on the call instruction, the 
>>>> >return value can be in register a6, a10, oder a14.
>>
>>> 
>>> Puzzled expression.  The ABI should specify which return-value 
>>> convention will be used?
>>> 
>>> I suspect you'll need to explain a little more about your architecture.
> 
> 
> Xtensa has register windows.  The call instruction determines how far
> the window shifts; the return value is always going to be in some fixed
> register (a0?) at the end of the function, but the caller has to choose
> which call instruction to use and expect the return value in the
> correct location based on that.

Keep going :-)  For instance, what logic determines the shift amount 
(the insn just reflects that decision), and how does the mechanism 
compare to ia64 and SPARC?

Andrew