2.15 pdp11-dec-aout gas and objdump

[Bill Farmer]

Hi

 

I wish to report three problems with version 2.15 of binutils when built with ./configure  --target=pdp11-dec-aout.

 

1. pdp11-dec-aout-gas produces an incorrect offset for the PDP11 SOB instruction. The offset is calculated by gas as a 6 bit negative number. The offset should be a 6 bit positive number and is subtracted from the PC by the processor at run time. The command to gas was pdp11-dec-aout-gas -a -o test.lst test.s. I have a potential fix for this, I have included it below as a context diff:

+----------------------------------------------------------------+

*** ./gas/config/tc-pdp11.c.old Sat Jun  8 08:37:15 2002
--- ./gas/config/tc-pdp11.c Mon Sep 13 21:49:32 2004
***************
*** 199,204 ****
--- 199,205 ----
      case BFD_RELOC_PDP11_DISP_6_PCREL:
        mask = 0x003f;
        shift = 1;
+       val = -val;
        break;
      default:
        BAD_CASE (fixP->fx_r_type);

+----------------------------------------------------------------+

 

2. pdp11-dec-aout-objdump -d disassembles the offset for the PDP SOB instruction incorrectly. The effect is to make the incorrect code generated by the above problem appear correct. I have a potential fix for this, I have included it below as a context diff:

+----------------------------------------------------------------+

*** ./opcodes/pdp11-dis.c.old Mon Dec  2 13:13:37 2002
--- ./opcodes/pdp11-dis.c Mon Sep 13 21:37:54 2004
***************
*** 342,348 ****
     case PDP11_OPCODE_REG_DISPL:
       {
         int displ = (opcode & 0x3f) << 10;
!        bfd_vma address = memaddr + (sign_extend (displ) >> 9);
         FPRINTF (F, OP.name);
         FPRINTF (F, AFTER_INSTRUCTION);
         print_reg (src, info);
--- 342,348 ----
     case PDP11_OPCODE_REG_DISPL:
       {
         int displ = (opcode & 0x3f) << 10;
!        bfd_vma address = memaddr - (displ >> 9);
         FPRINTF (F, OP.name);
         FPRINTF (F, AFTER_INSTRUCTION);
         print_reg (src, info);

+----------------------------------------------------------------+

 

3. pdp11-dec-aout-gas loses the offset for mode 7 index deferred address mode instructions, @x(Rn), where x is the offset. I have no fix for this. I think the problem is in the parse_op_no_deferred() and parse_op_noreg() functions in ./gas/config/tc-pdp11.c. I have a short section of code which illustrates this problem, and the above problems.

 

test.s:

+----------------------------------------------------------------+

    .title test
;
s:  clr r0
    mov $5,r1
1$: inc @(R0)+
    dec @x(R0)
    clr @x
    sob r1,1$
x:  nop
;
    .end

+----------------------------------------------------------------+

 

test.lst:

+----------------------------------------------------------------+

GAS LISTING test.mac    page 1
test

 

   1                    .title test
   2               ;
   3 0000 000A      s:  clr r0
   4 0002 C1150500      mov $5,r1
   5 0006 980A      1$: inc @(R0)+
   6 0008 F80A0000      dec @x(R0)  <<< Should be F80A1200
   7 000c 3F0A0200      clr @x      <<< This is correct
   8 0010 7A7E          sob r1,1$   <<< Should be 467E
   9 0012 A000      x:  nop
  10               ;
  11                    .end
GAS LISTING test.mac    page 2
test

 

DEFINED SYMBOLS
            test.mac:3      .text:00000000 s
            test.mac:9      .text:00000012 x

 

NO UNDEFINED SYMBOLS

+----------------------------------------------------------------+

 

Same code assembled by RT11 MACRO, $5 is misinterpreted as a

symbol, but the SOB and @x(Rn) address modes are correct.

+----------------------------------------------------------------+

TEST    MACRO V05.03B WEDNESDAY 14-SEP-94 00:11  PAGE 1

 

      1                                         .TITLE  TEST
      2                                 ;
      3 000000  005000                  S:      CLR     R0
      4 000002  016701  000000G                 MOV     $5,R1
      5 000006  005230                  1$:     INC     @(R0)+
      6 000010  005370  000022'                 DEC     @X(R0)
      7 000014  005077  000002                  CLR     @X
      8 000020  077106                          SOB     R1,1$
      9 000022  000240                  X:      NOP
     10                                 ;
     11         000001                          .END
TEST    MACRO V05.03B WEDNESDAY 14-SEP-94 00:11  PAGE 1-1
SYMBOL TABLE

 

S       000000R         X       000022R         $5    = ****** GX

 

. ABS.  000000    000   (RW,I,GBL,ABS,OVR)
        000024    001   (RW,I,LCL,REL,CON)
ERRORS DETECTED:  0

+----------------------------------------------------------------+

Output from pdp11-dec-aout-objdump -d test.o:

+----------------------------------------------------------------+

test.o:     file format a.out-pdp11

 

Disassembly of section .text:

 

00000000 <s>:
   0: 0a00            clr r0
   2: 15c1 0005       mov $5, r1
   6: 0a98            inc *(r0)+
   8: 0af8 0000       dec *0(r0)
   c: 0a3f 0002       clr *$12 <x>
  10: 7e7a            sob r1, 6 <s+0x6> <<< Wrong destination

 

00000012 <x>:
  12: 00a0            nop

+----------------------------------------------------------------+

 

I am happy to provide further information if required

 

Regards

Bill Farmer