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From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Arnd Bergmann <arnd@kernel.org>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	stable@vger.kernel.org,
	Dinghao Liu <dinghao.liu@zju.edu.cn>,
	linux-mtd@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mtd: diskonchip: work around ubsan link failure
Date: Tue,  9 Apr 2024 08:41:27 +0200
Message-Id: <20240409064128.91899-1-miquel.raynal@bootlin.com>
In-Reply-To: <20240405143015.717429-1-arnd@kernel.org>
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On Fri, 2024-04-05 at 14:30:04 UTC, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> I ran into a randconfig build failure with UBSAN using gcc-13.2:
> 
> arm-linux-gnueabi-ld: error: unplaced orphan section `.bss..Lubsan_data31' from `drivers/mtd/nand/raw/diskonchip.o'
> 
> I'm not entirely sure what is going on here, but I suspect this has something
> to do with the check for the end of the doc_locations[] array that contains
> an (unsigned long)0xffffffff element, which is compared against the signed
> (int)0xffffffff. If this is the case, we should get a runtime check for
> undefined behavior, but we instead get an unexpected build-time error.
> 
> I would have expected this to work fine on 32-bit architectures despite the
> signed integer overflow, though on 64-bit architectures this likely won't
> ever work.
> 
> Changing the contition to instead check for the size of the array makes the
> code safe everywhere and avoids the ubsan check that leads to the link
> error. The loop code goes back to before 2.6.12.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.

Miquel