Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751535AbdINPYf (ORCPT ); Thu, 14 Sep 2017 11:24:35 -0400 Received: from mail-pf0-f195.google.com ([209.85.192.195]:37965 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751328AbdINPYe (ORCPT ); Thu, 14 Sep 2017 11:24:34 -0400 X-Google-Smtp-Source: ADKCNb63K+1clx9NxaZT/XOucuO1MTZ3fHYlnW+xE1ztk+oiX0WjLHdWwpJyQTPZ5trQ8vG3ljO9dBiil21/MAuh2kM= MIME-Version: 1.0 In-Reply-To: References: <20170914110709.3591691-1-arnd@arndb.de> From: Geert Uytterhoeven Date: Thu, 14 Sep 2017 17:24:33 +0200 X-Google-Sender-Auth: lxDP6YSnxT2vX58O8a9jkBepB9Q Message-ID: Subject: Re: [PATCH] mtd: spi-nor: stm32-quadspi: avoid unintialized return code To: Ludovic BARRE 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 Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v8EFOfLm010162 Content-Length: 2738 Lines: 72 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. 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