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

[Ludovic BARRE]

On 09/14/2017 05:24 PM, Geert Uytterhoeven wrote:
> Hi Ludovic,
>
> On Thu, Sep 14, 2017 at 5:13 PM, Ludovic BARRE <ludovic.barre@xxxxxx> wrote:
> > On 09/14/2017 03:38 PM, Geert Uytterhoeven wrote:
> > > On Thu, Sep 14, 2017 at 1:06 PM, Arnd Bergmann <arnd@xxxxxxxx> 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: âretâ 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@xxxxxxxx>
> > > > ---
> > > >    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@xxxxxxxxxxxxxx
>
> 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