Re: as variable '$' have problem

[nick clifton]

Hi 研发部淡明杰,


> bug description: In my program, expression '$-label' is ok to pass(see attachment 
> file line 7&8) assemble, but 'lable-$' cannot pass

It is nothing to do with the $ symbol specifically.  Any undefined 
symbol will give you the same effect.  Eg:

  $ cat test.s
  foo:  
        nop
        .byte undef - foo
        .byte foo - undef

  % as test.s   
  foo.s: Assembler messages:
  foo.s:4: Error: can't resolve `.text' {.text section} - `undef' 
{*UND* section}

This is a known limitation of the assembler/linker.  Essentially the 
problem is that the linker supports a relocation to compute "symbol - 
value" but it does not support a relocation to compute "value - symbol".

So the third line in the example source above is resolved by the 
assembler into a zero byte value and a relocation that computes "undef - 
1".  But the assembler cannot create a relocation to compute "1 - undef" 
so it issues the error message.

Cheers
  Nick