Re: [RFC] fixing extract_struct_value_address

[Michael Snyder <msnyder@redhat.com>]

Jim Blandy wrote:
> 
> Michael Snyder <msnyder@redhat.com> writes:
> > Problem: Find a function's return value when it is a struct
> > returned by reference (thru a pointer).
> >
> > Solution level one: Take the value of the register that was
> > used by the caller to pass the struct return address.
> >
> > Shortcoming: that register isn't preserved, so may be clobbered.
> >
> > Solution level two: Save the struct_return address when it
> > is passed to store_struct_return (or push_arguments), and
> > recover it when it is needed by extract_struct_value_address.
> >
> > Shortcoming: Not reentrant.  Nested function calls will clobber it.
> >
> > Proposed solution: create a stack structure, and "push" the
> > struct_return address in store_struct_return, popping it in
> > extract_return_address.  If you can't find it on the stack,
> > then use the value of the appropriate arg0 register.
> >
> > I think this should work for most targets, so the code for
> > managing the stack can be shared.
> 
> Doesn't this stack push and pop exactly as the generic dummy frame
> stack does?  Couldn't we just add a `struct_return_addr' field to
> `struct dummy_frame'?

Mmmmm, yes and no... the generic dummy frame's data structure
is not implemented as a stack -- although now that you mention
it, maybe it should be.  Functionally it may act like one...

Adding such a field to the generic dummy frame is a good idea --
but some architectures don't use the generic dummy frames.