Re: m68hc11 %hi relocate problem with carry

[Sean Keys <skeys at ipdatasys dot com>]

Hi James,

Have a look at my latest XGATE patch. Actually it worked fine in the 
previous patch too but you would have to look at more than the opcode 
table file to notice that :).  It's a simple port to follow and it 
appears to work as it should.

Test case:
--------------------
xgate.s
-------------------
.globl _start
.sect .text
_start:
    ldw     r1, linksymbol
    ldw     r2, linksymbol+4
    rts
    nop

xgate-as xgate.s -defsym linksymbol=0x20fe -o xgate.o

xgate-objdump xgate.o -d

Disassembly of section .text:

00000000 <_start>:
   0:    f1 fe           ldl R1, #0xfe
   2:    f9 20           ldh R1, #0x20 Abs* 0x20fe <linksymbol>
   4:    f2 02           ldl R2, #0x02
   6:    fa 21           ldh R2, #0x21 Abs* 0x2102 <linksymbol+0x4>
   8:    02 00           rts
   a:    01 00           nop

Cheers,
Sean

On 03/02/2012 12:25 PM, James Murray wrote:
> I've found what appears to be a bug (or at least a limitation) when
> using a %hi assembler directive in m68hc11. This is supposed to return
> the high byte of the resolved symbol, but if the low byte overflows, the
> carry is missed.
>
> Could someone point me at some example code in other targets that I
> could study in order to fix m68hc11 ?
>
> Test case:
> ----------------
> s12test.s
> ----------------
> .globl _start
> .sect .text
>
> _start:
>      ldx     #linksymbol
>      ldy     #linksymbol+4
>
>      ldaa   #%hi (linksymbol+4)
>      ldab   #%lo (linksymbol+4)
>      tfr     d,y
>
>      rts
>
> ----------------
> build commands
> ----------------
> m68hc11-elf-as -m68hc12 -o t3.o s12test.s
> m68hc11-elf-ld -mm68hc12elfb -o t3 -defsym linksymbol=0x20fe t3.o
> m68hc11-elf-objdump -mm68hc12 -d t3
>
>
> ----------------
> before linking
> ----------------
> t3.o:     file format elf32-m68hc12
>
>
> Disassembly of section .text:
>
> 00000000<_start>:
>     0:	ce 00 00    	ldx	#0x0<_start>
> 			1: R_M68HC12_16	linksymbol
>     3:	cd 00 04    	ldy	#0x4<_start+0x4>
> 			4: R_M68HC12_16	linksymbol
>     6:	86 00       	ldaa	#0x0
> 			7: R_M68HC12_HI8	linksymbol
>     8:	c6 04       	ldab	#0x4
> 			9: R_M68HC12_LO8	linksymbol
>     a:	b7 46       	tfr	D,Y
>     c:	3d          	rts
>
>
>
> ----------------
> after linking
> ----------------
> Disassembly of section .text:
>
> 0000c000<_start>:
>      c000:	ce 20 fe    	ldx	#0x20fe<linksymbol>
>      c003:	cd 21 02    	ldy	#0x2102<linksymbol+0x4>
>      c006:	86 20       	ldaa	#0x20
>      c008:	c6 02       	ldab	#0x2
>      c00a:	b7 46       	tfr	D,Y
>      c00c:	3d          	rts
> ----------------
>
> Code at c006 is incorrect - should be ldaa #0x21 but the carry is
> missing.
>
> Part of the code in tc-m68hc11.c within md_apply_fix :
> ----------------
>      case BFD_RELOC_M68HC11_HI8:
>        value = value>>  8;
>        /* Fall through.  */
>
>      case BFD_RELOC_M68HC11_LO8:
>      case BFD_RELOC_8:
>      case BFD_RELOC_M68HC11_PAGE:
>        ((bfd_byte *) where)[0] = (bfd_byte) value;
>        break;
>
> ----------------
>
> Suggestions welcome.
>
> regards
>
> James Murray