linux-kernel - RE: [PATCH] cciss: Fix warnings during compilation under 32bitenvironment

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Message-ID: <558F4D473FD7FE419B019232BF2D37B401167D74@G3W0634.americas.hpqcorp.net>
Date:	Thu, 19 Apr 2007 16:27:26 -0000
From:	"Cameron, Steve" <Steve.Cameron@...com>
To:	"James Bottomley" <James.Bottomley@...elEye.com>,
	"Miller, Mike (OS Dev)" <Mike.Miller@...com>
Cc:	"Hisashi Hifumi" <hifumi.hisashi@....ntt.co.jp>,
	<akpm@...ux-foundation.org>, <jens.axboe@...cle.com>,
	<linux-kernel@...r.kernel.org>, <linux-scsi@...r.kernel.org>
Subject: RE: [PATCH] cciss: Fix warnings during compilation under 32bitenvironment


Something like 

if (sizeof(blah) > 4) {
   do all the assignments with shifts
}

might be slighly better since the CDB is already zeroed
by cmd_alloc() and doesn't need to be zeroed a 2nd time.

-- steve

-----Original Message-----
From: James Bottomley [mailto:James.Bottomley@...elEye.com]
Sent: Thu 4/19/2007 11:22 AM
To: Miller, Mike (OS Dev)
Cc: Hisashi Hifumi; akpm@...ux-foundation.org; jens.axboe@...cle.com; linux-kernel@...r.kernel.org; linux-scsi@...r.kernel.org; Cameron, Steve
Subject: RE: [PATCH] cciss: Fix warnings during compilation under 32bitenvironment
 
On Thu, 2007-04-19 at 16:12 +0000, Miller, Mike (OS Dev) wrote:
> > > Nak. You still haven't told where you saw these warnings. What 
> > > compiler are you using? I do not see these in my 32-bit environment.
> > 
> > I think it's seen with CONFIG_LBD=n on 32 bits
> > 
> > In that configuration, sector_t is a u32 (it's u64 even on 32 
> > bits with CONFIG_LBD=y).  The proposed code change is a 
> > simple cut and paste from the sd driver.
> 
> Isn't there a better way than testing each one?

It's not such a bad option.  The sizeof() test is compile time
determinable, so the compiler simply zeros the fields in the
CONFIG_LBD=n case and does the shift for CONFIG_LBD=y.  It certainly
never compiles to four inline condition checks.

James



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