Re: Illegal instruction

[Art Berggreen <art at acc dot com>]

Aklilu Noah wrote:
> 
> Hi
>         I am compiling code to run on m68306 micro using
> gcc 2.95.2, binutils 2.9.1 and newlib 1.8.2.  However I am
> encountering an illegal instruction when I call atexit from
> my crt0.S as shown below
> 
>         movel   IMM(__FINI_SECTION__),(sp)
>         jsr     SYM(atexit)
> 
> I traced through the code using the monitor and it made the jump
> to the atexit code but I dissambled the code and got the following
> (atexit is entered at 304a0)
> 
> $000304A0 4E56 0000       link.w        A6,#0   ?
> $000304A4 2079 0003 12FE  movea.l       ($312FE).L,A0   ?
> $000304AA 2268 0146       movea.l       ($146,A0),A1    ?
> $000304AE 4A89            DC.W          ?
> $000304B0 6608            bne.b         $304BA  ?
> $000304B2 43E8 014A       lea.l         ($14A,A0),A1    ?
> $000304B6 2149 0146       move.l        A1,($146,A0)    ?
> $000304BA 701F            moveq.l       #$1F,D0 ?
> $000304BC B0A9 0004       cmp.l         ($4,A1),D0      ?
> $000304C0 6C26            bge.b         $304E8  ?
> $000304C2 4878 0088       pea.l         ($88).W ?
> $000304C6 4EB9 0003 0500  jsr           ($30500).L      ?
> $000304CC 2240            movea.l       D0,A1   ?
> $000304CE 4A89            DC.W          ?
> $000304D0 6604            bne.b         $304D6  ?
> $000304D2 70FF            moveq.l       #$FF,D0 ?
> $000304D4 6026            bra.b         $304FC  ?
> $000304D6 42A9 0004       clr.l         ($4,A1) ?
> $000304DA 2079 0003 12FE  movea.l       ($312FE).L,A0   ?
> 
> The problem occurs at 304ae, where the illegal instruction
> is. Note that there are additional illegal instructions
> at 304CE.  The problem seems to go away if I comment out
> that section of crt0 and things run ok.
> 
> Not really actually malloc has a pointer (called from a test program to
> make sure it works) that seems to be uninitialized, eventhough I
> zero out the bss and shbss sections.  It causes an illegal memory access
> to occur which traps the monitor. It doesn't even get
> to call sbrk (I have it output a character when it is entered)
> before it dies.  But one problem at a time.
> 
> Noah Aklilu
> aklilu@nyquist.ee.ualberta.ca
> http://www.ee.ualberta.ca/~aklilu/
> "Integrity is something you do when no one is looking"
> 
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Not sure why your monitor didn't disassemble it, but my books indicate
that 0x4a89 is a TST.L A1 instruction.  This would be consistant with
the instructions surrounding it.

Art

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