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Re: m68k -- extb.l instruction


   Date: Thu, 21 Mar 1996 14:04:28 -0600 (CST)
   From: Joel Sherrill <joel@merlin.gcs.redstone.army.mil>

   While incorporating a 68360 board support package into RTEMS and updating
   tools, I tripped across this and wanted some feedback.  For CPUs w/o a
   bfffo instruction RTEMS has an SW implementation of bfffo which uses an
   extb.l instruction.  This worked correctly AFAIK for the 68000 and 68302 
   based BSPs using binutils 2.5.2.  As of binutils 2.6, this instruction was
   restricted to 020up and cpu32 which agrees with the m68k family
   programmer's reference manual.  But this leaves me confused -- what was
   actually being generated binutils 2.5.2 on the 68000/68302?  The code it
   generated worked.  Is this a hole in the m68k docs or just a fluke?  Does 
   this instruction really exist on the 68302?  

As far as I can see from the sources, gas has always restricted the
extb.l instruction to 68020up and cpu32.  This did not change between
the 2.5.2 and 2.6 releases.  I don't know why it was working for you
for 2.5.2.

Ian