Re: assembler relaxation

["nagaraju.m" <nagaraju dot m at redpinesignals dot com>]

Hi Nick,


Nick Clifton wrote:
> Hi Nagaraju,
>
> >    case 6:
> >    value = (long) (target_address - (address_of_var_part  + 4)) + 4;
> >    value >>= 1;
> >    switch (opcodep[0])
> >    {
> >        case BEZ:
> >        //printf("BEZ 16 value = %d\n",value);
> >        opcodep[2] = 0x54; //emit beq, insertng its opcode
> >        break;
> >        case BNEZ:
> >        //printf("BNEZ 16 value = %d\n",value);
> >        opcodep[2] = 0x94; //emit bne, insertng its opcode
> >        break;
> >    }
> >    opcodep[0] = 0x7; //insert cmp instruction instead of bez
> >    opcodep[3] = ( value & 0xff );//insert offset
> >    fixp = fix_new (fragp, fragp->fr_fix, 4, fragp->fr_symbol,
> >           fragp->fr_offset, 1, BFD_RELOC_RPINE_S8_PCREL);
> >    fixp->fx_pcrel_adjust = 2;
> >    fragp->fr_fix += 2;
>
> OK, so at this point you are presumably expecting that:
>
>   opcodep[0] contains the CMP instruction.
>   opcodep[1] contains zero.
(Nagaraju)          opcodep[1] contains the register which is to compared.
>   opcodep[2] contains the BEQ or BNE instruction.
>   opcodep[3] contains offset to LABEL.
>
> Right ?  But in some cases it would appear that opcodep[2] and 
> opcodep[3] are being replaced with zeroes.
(Nagaraju) absolutely right.
> Obviously some other part of the assembler is corrupting the contents 
> of the opcodep[] array.  If you have access to a debugger (eg gdb) I 
> would suggest that you run it and place a watchpoint on opcodep[2] and 
> opcodep[3] to see how they get corrupted.
(Nagaraju) I have kept the watchpoint at that location but no where it 
is getting hit.
> Without knowing more, my guess would be that it is connected with 
> how/where this opcodep[] array is declared.  Is it part of a bigger 
> structure that gets reused maybe ?
(Nagaraju)      opcodep[] is pointing to fragp->fr_opcode.
  
   it is declared in md_convert_frag
   {
     unsigned char *opcodep;

    opcodep = fragp->fr_opcode;
     
         ....
   }
> Cheers
>   Nick
Thanks,
Nagaraju