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

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Date:	Fri, 01 Oct 2010 09:27:29 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, <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

>>> On 01.10.10 at 02:26, "H. Peter Anvin" <hpa@...or.com> wrote:
> ... but that doesn't work with the macros like movq_cfi.  On those, we

Is that only because of the register names used as operands to
movq_cfi etc not having the % specified right away? I don't think
that is really needed, i.e. the % could go there rather than being
added in the macro body - the .cfi_* directives are perfectly happy
with having the prefix there (and I don't know why it was coded
this way in the first place, as this made it less similar to the plain
movq while I thought the goal was to keep the differences to a
minimum).

> 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!)
> 
> I'm completely lost about how to deal with this.   We can't simply
> defang the macros -- at least not in a way that is likely to *stay*
> working -- and dropping the macros is seriously going to impact the
> debuggability of the kernel.  One way, of course, is to simply declare
> binutils 2.16 and 2.15.9x (which is apparently included in
> RHEL/CentOS 4) to be broken beyond repair unless distros backport a fix,
> and in many ways I think that is the preferred option, but I don't know
> if that makes sense to others...

The other alternative, albeit disliked by Ingo, continues to be to use
__stringify() on all non-trivial operands, which then wouldn't require
suppressing CONFIG_AS_CFI for pre-2.17 binutils.

Jan

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