Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751476AbdINQ4x (ORCPT ); Thu, 14 Sep 2017 12:56:53 -0400 Received: from mx08-00178001.pphosted.com ([91.207.212.93]:55103 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751255AbdINQ4w (ORCPT ); Thu, 14 Sep 2017 12:56:52 -0400 Subject: Re: [PATCH] mtd: spi-nor: stm32-quadspi: avoid unintialized return code To: Geert Uytterhoeven CC: Arnd Bergmann , Cyrille Pitchen , Marek Vasut , Boris Brezillon , Alexandre Torgue , Richard Weinberger , "linux-kernel@vger.kernel.org" , MTD Maling List , "linux-arm-kernel@lists.infradead.org" , Maxime Coquelin , Brian Norris , David Woodhouse References: <20170914110709.3591691-1-arnd@arndb.de> From: Ludovic BARRE Message-ID: Date: Thu, 14 Sep 2017 18:55:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.75.127.44] X-ClientProxiedBy: SFHDAG2NODE2.st.com (10.75.127.5) To SFHDAG6NODE1.st.com (10.75.127.16) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-14_05:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2971 Lines: 80 On 09/14/2017 05:24 PM, Geert Uytterhoeven wrote: > Hi Ludovic, > > On Thu, Sep 14, 2017 at 5:13 PM, Ludovic BARRE wrote: >> On 09/14/2017 03:38 PM, Geert Uytterhoeven wrote: >>> On Thu, Sep 14, 2017 at 1:06 PM, Arnd Bergmann wrote: >>>> If we send zero-length data to stm32_qspi_tx_poll() on older >>>> compiler versions such as gcc-4.6, we get warned that the >>>> return code is uninitialized: >>>> >>>> drivers/mtd/spi-nor/stm32-quadspi.c:248:2: error: ‘ret’ may be used >>>> uninitialized in this function [-Werror=uninitialized] >>>> >>>> On newer compiler versions, the return code is always zero >>>> in this case, as the local variable gets optimized away and >>>> is assumed to be zero after the loop completes without error. >>>> >>>> This changes the function to instead return -EINVAL if it >>>> ever gets called with a zero length buffer. >>>> >>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82203 >>>> Signed-off-by: Arnd Bergmann >>>> --- >>>> drivers/mtd/spi-nor/stm32-quadspi.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/mtd/spi-nor/stm32-quadspi.c >>>> b/drivers/mtd/spi-nor/stm32-quadspi.c >>>> index 86c0931543c5..711cfe7aa4bf 100644 >>>> --- a/drivers/mtd/spi-nor/stm32-quadspi.c >>>> +++ b/drivers/mtd/spi-nor/stm32-quadspi.c >>>> @@ -227,7 +227,7 @@ static int stm32_qspi_tx_poll(struct stm32_qspi >>>> *qspi, >>>> void (*tx_fifo)(u8 *, void __iomem *); >>>> u32 len = cmd->len, sr; >>>> u8 *buf = cmd->buf; >>>> - int ret; >>>> + int ret = -EINVAL; >>>> >>>> if (cmd->qspimode == CCR_FMODE_INDW) >>>> tx_fifo = stm32_qspi_write_fifo; >>> >>> >>> See also "[PATCH] mtd: spi-nor: stm32-quadspi: Fix uninitialized error >>> return code" >>> (https://patchwork.kernel.org/patch/9842173/) >> >> hi Arnd, Geert >> >> sorry, I was forgot this thread while my holidays >> >> Geert: what do you mean like "similar bugs in the future" in "If you >> initialized ret at the beginning, you lose the ability to catch newly >> introduced similar bugs in the future." > > If you pre-initialize ret at the top, you loose the ability of the compiler > to detect at compile-time if ret is never written to later. It will just return > -EINVAL at runtime. > > With my version, if the code is modified later and another "return ret" is > added, the compiler will detect if there's a code path that forgets > to assign a value to ret. Ok, it's clear for me. I favor geert's solution. Arnd what do you think ? > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds >