Re: Bug in gas, with expressions in macros

[Nick Clifton]

Hi Brian,

> Does anyone know if this situation has been pursued at all? I still
> get the error in larger files despite having listings turned off. It
> appears that X_op ends up being O_subtract instead of O_constant
> when you do subtraction of two variables in the same memory section
> (or subtraction of two constants inside a macro that may or may not
> be in the same memory section). I'm interested in
> providing/finding/assisting with a fix for this problem. Please let
> me know if  you have anymore information. Thanks,


The problem, at least with listings enabled, is that the listing code
creates a new frag between each line.  This effectively seperates the
declaration of the label .__start_of_init__ in your example the
reference to it in the invocation of the VEC macro on the following
line:
        .macro VEC name
        .if ( . - .__start_of_init__ )
            .string "Hello"
        .endif
        .endm

   .__start_of_init__:

        VEC _vector_1

Since (at the time when the .if is being evaluated) frags can be
resized, it is impossible to calculate the value of ". -
.__start_of_init__" and hence the assembler complains about a
non-constant expression.

The fix, it seems to me, is to stop the listing code from creating a
new frag.  For example the attached patch will make your test code
assemble even when -an is specified.  I have not tested this patch
extensively however, and I suspect that it will interfere with proper
listing generation.  You might find it to be a starting point however.

Cheers
        Nick

Index: gas/listing.c
===================================================================
RCS file: /cvs/src/src/gas/listing.c,v
retrieving revision 1.19
diff -c -3 -p -w -r1.19 listing.c
*** gas/listing.c       18 May 2002 12:53:30 -0000      1.19
--- gas/listing.c       22 May 2002 15:33:05 -0000
*************** listing_newline (ps)
*** 390,397 ****
    last_line = line;
    last_file = file;
  
    new_frag ();
! 
    if (listing_tail)
      listing_tail->next = new;
    else
--- 388,396 ----
    last_line = line;
    last_file = file;
  
+ #if 0
    new_frag ();
! #endif
    if (listing_tail)
      listing_tail->next = new;
    else
*************** listing_newline (ps)
*** 408,416 ****
    new->hll_file = (file_info_type *) NULL;
    new->hll_line = 0;
    new->debugging = 0;
! 
    new_frag ();
! 
  #ifdef OBJ_ELF
    /* In ELF, anything in a section beginning with .debug or .line is
       considered to be debugging information.  */
--- 407,415 ----
    new->hll_file = (file_info_type *) NULL;
    new->hll_line = 0;
    new->debugging = 0;
! #if 0
    new_frag ();
! #endif
  #ifdef OBJ_ELF
    /* In ELF, anything in a section beginning with .debug or .line is
       considered to be debugging information.  */