Re: [PATCH] i386_stab_reg_to_regnum (4 <-> 5, ebp <-> esp)

[Brian Ford <ford@vss.fsi.com>]

On Fri, 2 Apr 2004, Eli Zaretskii wrote:
> Brian Ford wrote talking about DJGPP:
> > I just don't see any reason to try and be "compatible" with it.  I'm not
> > even sure what that means?  I certainly don't want to break it,
> > though.
>
> Well, the only way to break DJGPP is if you modify code used by it as
> well.  So any pieces of coffread.c or dwarf2read.c, or anything in
> i386-related files that is related to that, are possible areas of
> interest.  If you only change Windows-specific files, you cannot
> possibly break DJGPP (or any other non-Windows target).
>
I understand that.

Getting back to the original subject, we're talking about fixing
i386_stab_reg_to_regnum.  That would affect DJGPP.  All indications are,
however, that the patch is correct.  If it breaks other targets, then
those other targets will need to be fixed again ;-).

> However, what I'm really interested in is the possibility that a
> similar problem exists in the DJGPP port.
>
It should, I just haven't figured out how to show you, especially if the
target backend has already "fixed" it.

> > Eli Zaretskii wrote:
> > > I marked this thread for checking, but never had time to do it.  If
> > > you can send me a sample program and a description of what I should do
> > > to see whether DJGPP has the same problem, I will gladly try that and
> > > report the results.  Please also tell what versions of GCC and GDB
> > > should I try.
> > >
> > You mean source code, right?  You would obviously need a DJGPP toolchain
> > for testing.  I don't have one right now.
>
> Well, I do have it, obviously: otherwise, how could I possibly be
> maintaining the DJGPP port of GDB? ;-)
>
Sorry, I wasn't looking carefully and didn't know (blush...).

> > A sample program would be trivial, so you might as well make one yourself.
> > Just throw in some stack variables, preferably some in main, and some in
> > a function called from main.  Oh, and make a few of them floating point
> > so you can test that too.
>
> I understand this, but given my total lack of free time, I'd
> appreciate a specific worked-out example with commands you type and
> what GDB prints in response.  I don't mean for you to install the
> DJGPP development environment and try that, just do that with the
> Windows tools where you encountered the problem.  All I want to see is
> whether similar problems with EBP and ESP exist in the DJGPP port.
>
Ok, I'm trying to find a simple step-by-step.

As a quick test, does a simple "bt" for a DWARF 2 compiled program stop at
main, or run off infinately?  What about for stabs?  That's one way to
tell about ebp <-> esp, maybe.

Can you try Jim's example program here compiled for DWARF 2?

http://sources.redhat.com/ml/gdb-patches/2004-04/msg00025.html

Try an info address a in foo and see what you get.  That should confirm
Mark's suspicion about having the wrong register translation function for DWARF 2
on DJGPP.

Also, can you confirm the dumped DWARF info has a DW_AT_frame_base of
DW_OP_reg4, not 5?

How often does DJGPP use sdb, stabs, dwarf 2?  I just realized that DWARF
2 is not the default.

I've got to go out-of-town now for the weekend, but I'll work on an exact
step by step when I get back on Monday.

> Of course, if you are not interested to see whether other i386 targets
> have this problem, you are free to disregard my request.
>
I'm interested in fixing Cygwin.  I may need to change generic i386 code
to do that.  So, I guess I have to be interested ;-).

Thanks a lot for your help and comments.

-- 
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
Phone: 314-551-8460
Fax:   314-551-8444