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[Bug gas/6957] i386 NOPs must be derived from march not mtune

From: hjl dot tools at gmail dot com
Subject: [Bug gas/6957] i386 NOPs must be derived from march not mtune
Date: 12 Oct 2008 12:44:02 -0000

------- Additional Comments From hjl dot tools at gmail dot com  2008-10-12 
12:44 -------
(In reply to comment #6)
> Created an attachment (id=2997)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=2997&action=view)
> binutils-cvs-fix2-i386-nop.patch
> Add bitfield checking back to patch for .arch settings.
> First point, do you not first agree that choosing instructions based on mtune
> is seriously broken?
> The other point here is about compatibility. Yes, these CPUs are missing this
> one instruction but since most builds these days are i686 by default this will
> break on these systems for users. It's only been fortunate that GCC strips out
> mtune options to gas. The optimisation lost is minor.
> I'm obviously an unknown person but the link given shows Linus Torvalds 
> opinion
> on this which may or not mean much to you. 

For assembler, PROCESSOR_UNKNOWN means CPU will take any instructions,
including those new NOPs. If you want to limit NOPs to certain ISA,
XXX, you need to use -match=XXX/-mtune=XXX. I checked in a patch


Now you can use the .arch directive to limit NOPs to XXX.



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