Re: PATCH: Add --alt-nops=short|long to x86/x86-64 assemblers

["H. J. Lu" <hjl@lucon.org>]

On Thu, Jun 15, 2006 at 08:53:32AM +0100, Nick Clifton wrote:
> Hi H. J.
> 
> >x86/x86-64 assemblers don't support -mtune/-march/-mcpu.
> 
> Ahh.  How does the assembler know which instruction set variants are 
> valid then ?  (I am thinking of the all the different SSE, PowerNow, etc 
> variants).

By default, the x86/x86-64 assemblers take everything. You can limit
the instruction set with .arch directive. Until now, we never generate
instructions beyond i386 ourselves. So it isn't a problem.

> 
> >We need a switch to tell
> >assembler if the new nop instructions can be used at all. Secondly,
> >not all modern processors prefer "long" versions. We need another
> >switch to tell which kind of the new nop instructions should be used,
> >short or long.
> 
> In which case the default presumably ought to be the short version and 
> the long version should only be enabled if explicitly requested via a 
> command line switch.
> 
> >Maybe I should add -march= and -mtune= to assembler.
> 
> It sounds like it would be a good idea, although if it is only to 
> support this new feature then you may not want to go that far.

I am considering adding -mtune= and updating document to indicate that
all instructions are allowed by default. But I will do some experiment
first.


H.J.