linux-kernel - Re: [PATCH 1/3] mtd: nand: Add on-die ECC support

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Date:	Mon, 27 Apr 2015 15:53:07 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Richard Weinberger <richard@....at>
Cc:	Ben Shelton <ben.shelton@...com>, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org, dwmw2@...radead.org,
	punnaiah.choudary.kalluri@...inx.com
Subject: Re: [PATCH 1/3] mtd: nand: Add on-die ECC support

On Tue, Apr 28, 2015 at 12:42:18AM +0200, Richard Weinberger wrote:
> Am 28.04.2015 um 00:36 schrieb Ben Shelton:
> >>> When I build this without CONFIG_MTD_NAND_ECC_ON_DIE enabled, I get the
> >>> following warning here:
> >>>
> >>> In file included from drivers/mtd/nand/nand_base.c:46:0:
> >>> include/linux/mtd/nand_ondie.h: In function 'nand_read_subpage_on_die':
> >>> include/linux/mtd/nand_ondie.h:28:1: warning: no return statement in function returning non-void [-Wreturn-type]
> >>> include/linux/mtd/nand_ondie.h: In function 'nand_read_page_on_die':
> >>> include/linux/mtd/nand_ondie.h:34:1: warning: no return statement in function returning non-void [-Wreturn-type]
> >>>
> >>> Perhaps return an error code here, even though you'll never get past the BUG()?
> >>
> >> What gcc is this?
> >> gcc 4.8 here does not warn, I thought it is smart enough that this function does never
> >> return. Can it be that your .config has CONFIG_BUG=n?
> >> Anyway, this functions clearly needs a return statement. :)
> > 
> > gcc 4.7.2, and you are correct that I had CONFIG_BUG off.  :)
> 
> Yeah, just noticed that BUG() with CONFIG_BUG=n does not have
> a nonreturn attribute. So, gcc cannot know...

But it's an obvious infinite loop... all of my toolchains (4.2, 4.5,
4.6, 4.8) are able to compile this without complaining (gcc -Wall):

int test() { do { } while (1); }

Not sure if 4.7 is unique.

But hey, others are doing this, so why not join the crowd. e.g.:

include/asm-generic/pgtable.h-567-#ifndef __HAVE_ARCH_PMD_WRITE
include/asm-generic/pgtable.h-568-static inline int pmd_write(pmd_t pmd)
include/asm-generic/pgtable.h-569-{
include/asm-generic/pgtable.h:570:      BUG();
include/asm-generic/pgtable.h-571-      return 0;
include/asm-generic/pgtable.h-572-}
include/asm-generic/pgtable.h-573-#endif /* __HAVE_ARCH_PMD_WRITE */
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