Re: [PATCH] char: pcmcia: remove set but not used variable 'tmp'

[yukuai (C)]

On 2021/05/14 14:28, Arnd Bergmann wrote:
> On Fri, May 14, 2021 at 8:21 AM Yu Kuai <yukuai3@xxxxxxxxxx> wrote:
> > Fixes gcc '-Wunused-but-set-variable' warning:
> >
> > drivers/char/pcmcia/cm4000_cs.c:1053:16: warning: variable ‘tmp’
> > set but not used [-Wunused-but-set-variable]
> >
> > It is never used and so can be removed.
> >
> > Fixes: c1986ee9bea3 ("[PATCH] New Omnikey Cardman 4000 driver")
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Looks good to me. This was likely written that way at a time when some
> architecture implemented inb() as a macro, and ignoring its value
> would cause a different warning.
>
> Since you are already touching this file, can you have a look at this
> warning as well:
>
>     drivers/char/pcmcia/cm4000_cs.c: In function 'set_protocol':
> > > drivers/char/pcmcia/cm4000_cs.c:569:16: warning: iteration 4 invokes undefined behavior [-Waggressive-loop-optimizations]
>       569 |   pts_reply[i] = inb(REG_BUF_DATA(iobase));
>           |   ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
>     drivers/char/pcmcia/cm4000_cs.c:567:2: note: within this loop
>       567 |  for (i = 0; i < num_bytes_read; i++) {
>
> This looks like a preexisting problem that was uncovered by a patch
> that is now in linux-next to change the inb() definition once more,
> I got a report from the kernel build bot about it after I merged the
> patch into the asm-generic tree. It needs a range check on
> num_bytes_read, or a Kconfig check to ensure it is not built on
> architectures without working inb()/outb() operations.
>
>          Arnd
> .
Hi,

I'm not familar with the logical here, however, if io_read_num_rec_bytes
may get 'num_bytes_read' greater than 4, this loop will cause index out
of boundary. It make sense to me to add a range check. Futhermore, since
'num_bytes_read' is ensure to >= 4，I think we can change the loop to:

for (i = 0; i < 4; ++i) {
	xoutb(i, REG_BUF_ADDR(iobase));
	pts_reply[i] = inb(REG_BUF_DATA(iobase));
}

Thanks
Yu Kuai