Re: [PATCH] x86: Add .nop directive to assembler

["Jan Beulich" <JBeulich at suse dot com>]

>>> On 15.02.18 at 16:02, <matz@suse.de> wrote:
> Hi,
> 
> On Thu, 15 Feb 2018, Jan Beulich wrote:
> 
>> >> > I also think extending .fill feels more natural.
>> >> >
>> >> 
>> >> No, .fill isn't what we want.
>> > 
>> > I fat-fingered that one, yes I meant .fill.
>> 
>> .fill again? Didn't you mean to write .skip this time?
> 
> Sigh.  It seems my fingers are unusually fat in this thread.  .skip, 
> dammit! .skip, .skip, .skip!
> 
>> Having thought about this some more - since currently FILL is expected 
>> to be an expression, none of the above is really suitable.
> 
> Well, that could be easily rectified.  Something along the lines of:

I didn't make the remark because of foreseeing any issues with
coding this up, but because @NOP (or any of your other
suggestions) could actually be a valid symbol name, which could be
valid to use here even if it's not part of any expression in case it's
an absolute one (e.g. an equate). The leading @ is undesirable
anyway because of ARM's use of it as a comment char.

Jan

> diff --git a/gas/read.c b/gas/read.c
> index 7bf52f1..8730318 100644
> --- a/gas/read.c
> +++ b/gas/read.c
> @@ -3326,6 +3326,7 @@ s_space (int mult)
>    char *stop = NULL;
>    char stopc = 0;
>    int bytes;
> +  bfd_boolean do_nops = FALSE;
>  
>  #ifdef md_flush_pending_output
>    md_flush_pending_output ();
> @@ -3386,7 +3387,12 @@ s_space (int mult)
>    if (*input_line_pointer == ',')
>      {
>        ++input_line_pointer;
> -      expression (&val);
> +      SKIP_WHITESPACE ();
> +      if (!strncasecmp (input_line_pointer, "@NOP", 4)
> +         && (input_line_pointer[4] == ' ' || !input_line_pointer[4]))
> +       do_nops = TRUE, input_line_pointer += 4;
> +      else
> +       expression (&val);
>      }
>    else
>      {
> 
>> How about "nop" (including the quotes) instead?
> 
> Also possible, yeah.
> 
> 
> Ciao,
> Michael.