linux-kernel - Re: sb_edac 32-bit compile fail due to 64-bit divide

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Message-ID: <20111103144347.GG19809@zod.bos.redhat.com>
Date:	Thu, 3 Nov 2011 10:43:47 -0400
From:	Josh Boyer <jwboyer@...hat.com>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
Cc:	linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: sb_edac 32-bit compile fail due to 64-bit divide

On Thu, Nov 03, 2011 at 12:32:31PM -0200, Mauro Carvalho Chehab wrote:
> Em 03-11-2011 12:07, Josh Boyer escreveu:
> > Hi,
> > 
> > It seems the newly added EDAC driver for SandyBridge won't build on
> > 32-bit x86 because of a 64-bit divide somewhere:
> > 
> > 	drivers/edac/sb_edac.c: In function 'get_memory_error_data':
> > 	drivers/edac/sb_edac.c:861:2: warning: left shift count >= width of type
> > 	[enabled by default]
> > 	<snip>
> > 	ERROR: "__udivdi3" [drivers/edac/sb_edac.ko] undefined!
> > 	make[1]: *** [__modpost] Error 1
> > 	make: *** [modules] Error 2
> > 
> > You can find the full build log here:
> > 
> > http://koji.fedoraproject.org/koji/getfile?taskID=3482579&name=build.log
> > 
> > Before I go digging into where this is done and what to do about it, I
> > do want to confirm that it is supposed to work on a 32-bit kernel,
> > correct?
> 
> Thanks for pointing it!
> 
> Well, I didn't test it on a 32-bit kernel. It should work through.
> 
> It is probably due to those debug lines:
> 	debugf0("CH#%d RIR#%d INTL#%d, offset %Lu.%03Lu GB (0x%016Lx), tgt: %d, reg=0x%08x\n",
>         	i, j, k,
>                 tmp_mb / 1000, tmp_mb % 1000,
>                 ((u64)tmp_mb) << 20L,
>                 (u32)RIR_RNK_TGT(reg),
>                 reg);
> (same kind of calculus is recurrent at the driver)

All of that should basically not exist in this build because the debugf*
macros depend on CONFIG_EDAC_DEBUG, which isn't set in this build.  The
problem seems to be somewhere else.

I would guess line 1056:

	addr /= sck_xch;

addr is a u64.

> Maybe the easiest way would be to write a function that would call do_div() internally,
> and output a string with something similar to:
> 
> 	sprintf(msg, "%Lu.%03Lu GB", tmp_mb / 1000, tmp_mb % 1000);
> 
> Of course, an interim fix would be to make it depend on CONFIG_64BIT or CONFIG_X86_64.

That would work I guess.  It's up to you.
> 
> Regards,
> Mauro
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