Re: IA32: printing FP register variables

[Jim Blandy <jimb@cygnus.com>]

So, here's the question I asked and the response I got from SCO's
compiler fellow (I assume):

Jim> Could you ask your compiler/debugger guys how their compilers
Jim> number the IA32 FP registers?  If they assign a fixed register
Jim> number to each ST(i), could you ask them how the debugger finds
Jim> the right ST(i) for a given variable while the stack is being
Jim> pushed and popped?  That is, a variable which lives in ST(4) at
Jim> one point will find itself in ST(6) after two FLD instructions,
Jim> and in ST(5) after an FADDP.  How would the debugger find the
Jim> variable at each point?  Or does the debugger just lose when
Jim> there are intermediate values on the FP stack?

"SCF" == "SCO's compiler fellow", who apparently doesn't want his real
name on public mailing lists:

SCF> Well, I don't have a good answer for you.  Our compiler basically
SCF> puts out information for the stack location of an automatic
SCF> floating-point variable.  It does not trace the location as it
SCF> moves to the floating-point stack.  As you say, the debugger
SCF> "just loses" when there are intermediate values on the FP stack.
SCF> I suppose you could use DWARF2 location lists to track the
SCF> variable with each floating-point push/pop.

So I guess nobody does this right.  Heh.  I thought so.