[PATCH] x86: Add .nop directive to assembler

Jan Beulich JBeulich@suse.com
Thu Feb 15 16:08:00 GMT 2018


>>> On 15.02.18 at 16:50, <matz@suse.de> wrote:
> Hi,
> 
> On Thu, 15 Feb 2018, Jan Beulich wrote:
> 
>> >> 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).
> 
> Well, then I don't see other ways of special casing something that also is 
> a valid expression right now, like your string suggestion.  The problem of 
> course being that this would reinterpret currently valid (though 
> strange) directives into something else.  Right now
>   .skip 10, "foo"
> is equivalent to
>   .skip 10, foo
> and results in 10 one-byte relocs against symbol 'foo'.  We'd reinterpret 
> this, which may be fine, but needs to be a conscious decision.

Oh, right, symbol names may be quoted now.

>> The leading @ is undesirable anyway because of ARM's use of it as a 
>> comment char.
> 
> Sure, other prefix chars could be used, e.g. one of the binary operators 
> in expressions.  But in light of the above it might not be such a bright 
> idea to extend .skip after all.

Well, if we can fine a universally usable escape character, things
ought to be fine this way. Apart from binary operator chars which
aren't also unary operator ones, \ would come to mind.

Jan



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