Re: [RFC PATCH] ARM: Use generic BUG() handler
From: Simon Glass
Date: Tue Mar 01 2011 - 11:34:55 EST
On Tue, Mar 1, 2011 at 2:03 AM, Russell King - ARM Linux
<linux@xxxxxxxxxxxxxxxx> wrote:
> On Tue, Mar 01, 2011 at 10:12:40AM +0100, Mikael Pettersson wrote:
>> Russell King - ARM Linux writes:
>> > 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.
>>
>> What's the gcc bugzilla bug number?
>
> No idea off hand - I'll have to search for that.
>
It seems I am lucky with the gcc I am using. I would have thought this
would be a pretty fundamental feature, but yes I did notice that %c
wasn't used anywhere.
Would this kernel feature be acceptable as a selectable config option
on ARM then?
Thanks,
Simon
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