🚀 go-pugleaf

To all 68020 developers using the GNU assembler (GAS):

** There is a bug in GAS version 1.37 that causes it to incorrectly
** assemble the MOVEM instruction in some cases.

The bug occurs when:
  (1) the instruction is being assembled in the TEXT segment;
  (2) the transfer is memory --> register(s)  (memory is the data source);
  (3) the Effective Address (EA) is known (not an external reference);
  (4) the EA is in the TEXT segment; and
  (5) the EA is absolute (no indirection or indexing).

Why it breaks:
   GAS has a special test for absolute address references to text
   segment locations, and it converts them into PC-relative addresses.
   Although the GAS code in m68k.c and m68k-opcodes.h looks like it
   ought to work, it clearly doesn't.

What you get:
   GAS produces <instruction> <offset>  <reglist>
   instead of   <instruction> <reglist> <offset>  as it ought to.

Work-around:
   Use data segment memory.  It's a bit odd to be using text segment
   locations to save register values anyway.

Comparison of v1.37 and v1.38 GAS source code files indicates that
v1.38 has the bug, too.
 -WBE

Other notes for bug-gnu:
* running on SunOS 4.1, cross assembling for Sun3
* assemble the following with "gas -mc68020 -o bug bug.s"

---------------------------------------------------------------------------
.text
foo:	.skip	0x50

	moveml	foo,d0-d7/a0-a7
---------------------------------------------------------------------------

* assembles: 0x50/  4cfa ffae ffff, but should have ffff as second word,
  not third.
 -WBE