Re: find_saved_register(frame) -> next/prev frame?

[Elena Zannoni <ezannoni at cygnus dot com>]

Andrew Cagney writes:
 > Hello,
 > 
 > The function find_saved_register() uses:
 > 
 >   /* Note that this next routine assumes that registers used in
 >      frame x will be saved only in the frame that x calls and
 >      frames interior to it.  This is not true on the sparc, but the
 >      above macro takes care of it, so we should be all right. */
 >   while (1)
 >     {
 >       QUIT;
 >       frame1 = get_prev_frame (frame1);
 >       if (frame1 == 0 || frame1 == frame)
 >         break;
 >       FRAME_INIT_SAVED_REGS (frame1);
 >       if (frame1->saved_regs[regnum])
 >         addr = frame1->saved_regs[regnum];
 >     }
 > 
 > find the frame that contains a registers value.  I'm right now very
 > confused as I think it is looking in the wrong direction.
 > 
 > Consider the stack:
 > 
 > 	main()
 > 	-> outer ()
 > 	   saves r1, r2
 > 	-> middle ()
 > 	   saves r2, r3
 > 	-> inner()
 > 	   saves r1, r3
 > 
 > lets assume that we've just selected the frame for middle().  I think we
 > should find register values at:
 > 
 > 	r1: in inner()' stack frame
 > 	r2: in the register cache
 > 	r3: in inner()'s stack frame
 > 
 > Looking at the above implementation.  My understanding of
 > ``get_prev_frame()'' is that it goes to the next _outer_ frame.  It
 > should be calling get_next_frame() going to the next inner frame.  It
 > also appears to contract the comment attatched to the code.
 > 
 > Can I rename get_next_frame() to get_inner_frame() and get_prev_frame()
 > to get_outer_frame() :-)
 > 
 > 	Andrew
 > 
 > PS: I should note that this code has remained largely unchanged since
 > '91 (which is as far back as CVS history goes!) so either something
 > really wierd is going on or I'm missing something obvious - I guess we
 > suspect the latter.

It seems that find_saved_register is called only by mips_get_saved_register()
and default_get_saved_register().

There is another function, generic_get_saved_register() in
blockframe.c which is basically identical to
default_get_saved_register and which doesn't call
find_saved_register(). Maybe the author realized that
find_saved_register() was wrong, but didn't want to touch the exisitng
code.

Probably we should switch the macro GET_SAVED_REGISTER to be
generic_get_saved_register instead of default_get_saved_register and
see what happens.

Elena