From: Martin Str|mberg <ams AT ludd DOT luth DOT se>
Message-Id: <200101231735.SAA21377@father.ludd.luth.se>
Subject: Re: Debugging on 386
In-Reply-To: <3405-Mon22Jan2001221957+0200-eliz@is.elta.co.il> from Eli Zaretskii at "Jan 22, 2001 10:19:58 pm"
To: djgpp-workers AT delorie DOT com
Date: Tue, 23 Jan 2001 18:35:52 +0100 (MET)
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According to Eli Zaretskii:
> > -> c
> > Breakpoint 1, main (argc=1, argv=0x905d4) at analyse_ints.c:129
> > 129       if( argc != 2)
> > -> bt
> > #0  main (argc=1, argv=0x905d4) at analyse_ints.c:129
> > #1  0x3368 in __crt1_startup ()
> > -> n
> > Exiting due to signal SIGFPE
> 
> This one is not.  What does "disassemble analyse_ints" print near the
> EIP of the breakpoint (0x1a64)?  Do you see any FP instructions
> anywhere around that?

Here's the disassembly (-> disass main):
Dump of assembler code for function main:
0x1a58 <main>:  push   %ebp
0x1a59 <main+1>:        mov    %esp,%ebp
0x1a5b <main+3>:        sub    $0x7c,%esp
0x1a5e <main+6>:        push   %edi
0x1a5f <main+7>:        push   %esi
0x1a60 <main+8>:        push   %ebx
0x1a61 <main+9>:        mov    0xc(%ebp),%edx
0x1a64 <main+12>:       cmpl   $0x2,0x8(%ebp)
0x1a68 <main+16>:       je     0x1a84 <main+44>
0x1a6a <main+18>:       mov    (%edx),%eax
0x1a6c <main+20>:       add    $0xfffffff8,%esp
0x1a6f <main+23>:       push   %eax
0x1a70 <main+24>:       push   $0x1810
0x1a75 <main+29>:       call   0x3800 <printf>
0x1a7a <main+34>:       add    $0xfffffff4,%esp

As you can see no floating point instructions anywhere.

> > Coprocessor Error at eip=00001a64, x87 status=
> > Program received signal SIGEMT, Emulation trap.
> > 0x9611 in _status87 ()
> > -> bt
> > #0  0x9611 in _status87 ()
> > #1  0x47da in do_faulting_finish_message ()
> > #2  0x4d13 in __djgpp_traceback_exit ()
> > #3  0x4da0 in raise ()
> > #4  0x2c3a in nofpsig ()
> > #5  0x4daa in raise ()
> > #6  0x4e07 in __djgpp_exception_processor ()
> > #7  0x1 in ?? ()
> > #8  0x3368 in __crt1_startup ()
> 
> This is expected: the code which prints the traceback calls
> _status87.  But what is that 0x1 on the stack?

I can't explain it but it seems to be the value of argc (or a copy of
it) because if I try to run the program with "r a" it becomes 0x2 and
with "r 2 b" it becomes 0x3.


Right,

						MartinS