linux-kernel - Re: [PATCH] mtd: spi-nor: stm32-quadspi: avoid unintialized return code

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Date:   Thu, 14 Sep 2017 17:13:06 +0200
From:   Ludovic BARRE <ludovic.barre@...com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>
CC:     Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Marek Vasut <marek.vasut@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Richard Weinberger <richard@....at>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] mtd: spi-nor: stm32-quadspi: avoid unintialized return
 code

hi Arnd, Geert



On 09/14/2017 03:38 PM, Geert Uytterhoeven wrote:
> Hi Arnd,
> 
> On Thu, Sep 14, 2017 at 1:06 PM, Arnd Bergmann <arnd@...db.de> 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 <arnd@...db.de>
>> ---
>>   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."

> 
> Gr{oetje,eeting}s,
> 
>                          Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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
>