On Mon, May 09, 2022 at 05:43:58AM -0700, Tom Rix wrote:
>
> On 5/9/22 5:11 AM, Dan Carpenter wrote:
> > The type needs to be u8. The type was accidentally changed to char as
> > a cleanup. Unfortunately, that meant that the zynq_fpga_has_sync()
> > function never returns true. This bug was detected by Smatch and Clang:
> >
> > drivers/fpga/zynq-fpga.c:245 zynq_fpga_has_sync() warn: impossible condition '(buf[2] == 153) => ((-128)-127 == 153)'
> > drivers/fpga/zynq-fpga.c:246 zynq_fpga_has_sync() warn: impossible condition '(buf[3] == 170) => ((-128)-127 == 170)'
> >
> > drivers/fpga/zynq-fpga.c:246:14: warning: result of comparison of
> > constant 170 with expression of type 'const char' is always false
> > [-Wtautological-constant-out-of-range-compare]
> > buf[3] == 0xaa)
> > ~~~~~~ ^ ~~~~
> > drivers/fpga/zynq-fpga.c:245:50: warning: result of comparison of
> > constant 153 with expression of type 'const char' is always false
> > [-Wtautological-constant-out-of-range-compare]
> > if (buf[0] == 0x66 && buf[1] == 0x55 && buf[2] == 0x99 &&
> > ~~~~~~ ^ ~~~~
> >
> > Fixes: ada14a023a64 ("fpga: zynq: Fix incorrect variable type")
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > ---
> > The ada14a023a64 ("fpga: zynq: Fix incorrect variable type") patch went
> > through six of revisions. The kbuild bug found this bug early on
> > but the author ingored kbuild-bot and kept resending the buggy patch
> > anyway.
> >
> > After the patch was merged then I sent a separate bug report and Xu
> > Yilun asked about why only the author was on the CC list for the first
> > bug reports. A valid question, definitely. I will poke the kbuild
> > devs about this.
> >
> > Hm... Actually looking through the list there have been a bunch of bug
> > reports about this because both Smatch and Clang complain so kbuild
> > sends duplicate warnings for this type of bug. And then kbuild
> > sends another to say "This issue is still remaining" warning. And then
> > Xu Yilun sent an email "Kbuild-bot is still complaining. Please don't
> > forget to fix this." So that's at least four public emails about this
> > and one or two private emails directly from kbuild-bot to the author.
> >
> > The kbuild-bot wanted to send *another* warning today, but I decided to
> > send a fix instead.
> >
> > LOL.
> >
> > drivers/fpga/zynq-fpga.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/fpga/zynq-fpga.c b/drivers/fpga/zynq-fpga.c
> > index 6beaba9dfe97..426aa34c6a0d 100644
> > --- a/drivers/fpga/zynq-fpga.c
> > +++ b/drivers/fpga/zynq-fpga.c
> > @@ -239,7 +239,7 @@ static irqreturn_t zynq_fpga_isr(int irq, void *data)
> > * the correct byte order, and be dword aligned. The input is a Xilinx .bin
> > * file with every 32 bit quantity swapped.
> > */
> > -static bool zynq_fpga_has_sync(const char *buf, size_t count)
> > +static bool zynq_fpga_has_sync(const u8 *buf, size_t count)
>
> This is called from zynq_fpga_ops_write_init, a fpga_manager_ops function
> that
>
> uses 'const char *' as a type for its write() buf's.
>
> I think const u8 * would be a better type for all of the fpga_manager
> instances.
I don't think it's necessary to change the write_init(), const char *buf
is fine.
For this case, if the cleanup is necessary, just type casting the buf.
zynq_fpga_has_sync((const u8 *)buf, count)
Thanks,
Yilun
>
> If folks agree, I'll make the change.
>
> Tom
>
> > {
> > for (; count >= 4; buf += 4, count -= 4)
> > if (buf[0] == 0x66 && buf[1] == 0x55 && buf[2] == 0x99 &&
