RE: [PATCH 5/6] fix warning on test_ti_thread_flag()

Geert Uytterhoeven
2006-01-25T17:19:15Z

On Wed, 25 Jan 2006, Chen, Kenneth W wrote:
> Geert Uytterhoeven wrote on Wednesday, January 25, 2006 4:29 AM
> > On Wed, 25 Jan 2006, Akinobu Mita wrote:
> > > If the arechitecture is
> > > - BITS_PER_LONG = 64
> > > - struct thread_info.flag 32 is bits
> > > - second argument of test_bit() was void *
> > >
> > > Then compiler print error message on test_ti_thread_flags()
> > > in include/linux/thread_info.h
> > >
> > > Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
> > > ---
> > > thread_info.h | 2 +-
> > > 1 files changed, 1 insertion(+), 1 deletion(-)
> > >
> > > Index: 2.6-git/include/linux/thread_info.h
> > > =================================> > > --- 2.6-git.orig/include/linux/thread_info.h 2006-01-25
> 19:07:12.000000000 +0900
> > > +++ 2.6-git/include/linux/thread_info.h 2006-01-25
> 19:14:26.000000000 +0900
> > > @@ -49,7 +49,7 @@
> > >
> > > static inline int test_ti_thread_flag(struct thread_info *ti, int
> flag)
> > > {
> > > - return test_bit(flag,&ti->flags);
> > > + return test_bit(flag, (void *)&ti->flags);
> > > }
> >
> > This is not safe. The bitops are defined to work on unsigned long
> only, so
> > flags should be changed to unsigned long instead, or you should use a
> > temporary.
> >
> > Affected platforms:
> > - alpha: flags is unsigned int
> > - ia64, sh, x86_64: flags is __u32
> >
> > The only affected 64-platforms are little endian, so it will silently
> work
> > after your change, though...
>
> I thought test_bit can operate on array beyond unsigned long.
> It's perfectly legitimate to do: test_bit(999, bit_array) as
> long as bit_array is indeed big enough to hold 999 bits. It
> is the responsibility of the caller to make sure that the
> underlying array is big enough for the bit that is being tested.

Yes, it can operate on arrays of unsigned long.

> I don't think you need to change the flags size.

Passing a pointer to a 32-bit entity to a function that takes a pointer to a
64-bit entity is a classical endianness bug. So it's better to change it,
before people copy the code to a big endian platform.

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