linux-kernel - Re: gas 2.16 and assembly macros -- entry

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Message-ID: <20101005075107.GC23608@elte.hu>
Date:	Tue, 5 Oct 2010 09:51:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Jan Beulich <JBeulich@...ell.com>, heukelum@...tmail.fm,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: gas 2.16 and assembly macros -- entry_64.S build failure


* Avi Kivity <avi@...hat.com> wrote:

>  On 10/04/2010 08:23 PM, H. Peter Anvin wrote:
> >On 10/04/2010 09:20 AM, Avi Kivity wrote:
> >>    On 10/04/2010 05:43 PM, H. Peter Anvin wrote:
> >>>  On 10/04/2010 03:04 AM, Avi Kivity wrote:
> >>>>    On 10/01/2010 02:26 AM, H. Peter Anvin wrote:
> >>>>>   ... but that doesn't work with the macros like movq_cfi.  On those, we
> >>>>>   could argue that at least people won't put $ on them, but cpp will still
> >>>>>   split them apart with spaces; this apparently causes problems at least
> >>>>>   as soon as there is an expression more complicated than addition
> >>>>>   involved (apparently plus signs are okay, but minus signs aren't!)
> >>>>
> >>>>   Likely due to the fact that a minus sign can later join with a number
> >>>>   and become a new token, but a plug sign cannot.
> >>>>
> >>>
> >>>  ... except the same thing applies to other operators, other than the
> >>>  plus sign.  This kind of characterization is insanely frustrating, and
> >>>  really doesn't seem to follow logical rules ... we had a previous one
> >>>  where changing a macro name from upper case to lower case made gas 2.16
> >>>  work...
> >>>  	
> >>
> >>  Well, / and * do join.  % doesn't.  In a way, + does.
> >>
> >>  cpp is not a pure text processing language.  It's specifically geared to
> >>  C, and is fairly creaky when applying it to something other than C (and
> >>  is only somewhat creaky when applying it to C).
> >>
> >
> >The problem isn't with cpp, though, it's with gas.  There are bugs in
> >the gas 2.16 macro features that don't apply to any other gas version,
> >before *or* after.
> 
> I see.
> 
> I suppose it isn't possible to refuse to build with the broken version?

We could leave it build-broken and ask for a version specific quirk that 
runs a simple sed script over the source to turns 'pushl_cfi' et al into 
'push', or so?

Thanks,

	Ingo
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