Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Thu, 14 Sep 2017 17:24:33 +0200 | Subject | Re: [PATCH] mtd: spi-nor: stm32-quadspi: avoid unintialized return code |
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Hi Ludovic,
On Thu, Sep 14, 2017 at 5:13 PM, Ludovic BARRE <ludovic.barre@st.com> wrote: > On 09/14/2017 03:38 PM, Geert Uytterhoeven wrote: >> On Thu, Sep 14, 2017 at 1:06 PM, Arnd Bergmann <arnd@arndb.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@arndb.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."
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
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