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Re: [RFC] fixing extract_struct_value_address
- From: Michael Snyder <msnyder at redhat dot com>
- To: Jim Blandy <jimb at redhat dot com>
- Cc: gdb-patches at sources dot redhat dot com, kevinb at redhat dot com, cagney at redhat dot com
- Date: Thu, 22 Aug 2002 10:53:15 -0700
- Subject: Re: [RFC] fixing extract_struct_value_address
- Organization: Red Hat, Inc.
- References: <3D6418C5.FBF117D@redhat.com> <vt23ct7791w.fsf@zenia.red-bean.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.