linux-kernel - Re: [RFC PATCH] ARM: Use generic BUG() handler

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Message-ID: <20110301085911.GB16733@n2100.arm.linux.org.uk>
Date:	Tue, 1 Mar 2011 08:59:11 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Simon Glass <sjg@...omium.org>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Phil Carmody <ext-phil.2.carmody@...ia.com>,
	Tony Lindgren <tony@...mide.com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org, Rabin Vincent <rabin@....in>,
	Alexander Shishkin <virtuoso@...nd.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Joe Perches <joe@...ches.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH] ARM: Use generic BUG() handler

On Tue, Mar 01, 2011 at 08:49:49AM +0000, Russell King - ARM Linux wrote:
> On Mon, Feb 28, 2011 at 04:27:43PM -0800, Simon Glass wrote:
> > +	asm volatile("1:\t.word %c3\n"				\
> > +		     ".pushsection __bug_table,\"a\"\n"		\
> > +		     "2:\t.word 1b, %c0\n"			\
> > +		     "\t.hword %c1, 0\n"			\
> > +		     "\t.org 2b+%c2\n"				\
> 
> %c doesn't work on lots of versions of gcc, which is why we can't use
> the generic bug support.  There's no way to reliably generate constants
> without many compiler versions spitting out a '#' before them.

gcc 4.3.2:

asm(".word %c0" : : "i" (0));

produces:

        .word #0

which gas chokes on:

/tmp/cc2hGOHd.s:12: Error: bad expression
/tmp/cc2hGOHd.s:12: Error: junk at end of line, first unrecognized character is `0'

So what this means is that it's impossible to generate constants in
assembly with GCC targetting ARM without having them prefixed by '#',
which in turn makes it impossible to use the generic BUG support.

I reported this bug to gcc folk many years ago.  I've no idea which
version it has been fixed in or if it's even been fixed.
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