| Message ID | 1415098697-16304-1-git-send-email-maxime.coquelin@st.com |
|---|---|
| State | New |
| Headers | show |
On Tue, Nov 04, 2014 at 11:58:17AM +0100, Maxime COQUELIN wrote: > On some 32 bits architectures, including x86, GENMASK(31, 0) returns 0 > instead of the expected ~0UL. > > This is the same on some 64 bits architectures with GENMASK_ULL(63, 0). > > This is due to an overflow in the shift operand, 1 << 32 for GENMASK, > 1 << 64 for GENMASK_ULL. > > Fixes: 10ef6b0dffe404bcc54e94cb2ca1a5b18445a66b > Cc: <stable@vger.kernel.org> #v3.13+ > Reported-by: Eric Paire <eric.paire@st.com> > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com> There doesn't appear to be a clear maintainer for this file, so I'll try and stick in in tip. Thanks! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On Tue, Nov 04 2014, Maxime COQUELIN <maxime.coquelin@st.com> wrote: > -#define GENMASK(h, l) (((U32_C(1) << ((h) - (l) + 1)) - 1) << (l)) > -#define GENMASK_ULL(h, l) (((U64_C(1) << ((h) - (l) + 1)) - 1) << (l)) > +#define GENMASK(h, l) \ > + ((~0UL >> (BITS_PER_LONG - ((h) - (l) + 1))) << (l)) > + > +#define GENMASK_ULL(h, l) \ > + ((~0ULL >> (BITS_PER_LONG_LONG - ((h) - (l) + 1))) << (l)) Slightly bikeshedding here, but may I suggest spelling it (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h)))) ? This will ensure the arguments are expanded once each, and will, IMHO, DTRT if/when l > h (namely, yield 0). Rasmus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On 11/05/2014 12:10 PM, Rasmus Villemoes wrote: > On Tue, Nov 04 2014, Maxime COQUELIN <maxime.coquelin@st.com> wrote: > >> -#define GENMASK(h, l) (((U32_C(1) << ((h) - (l) + 1)) - 1) << (l)) >> -#define GENMASK_ULL(h, l) (((U64_C(1) << ((h) - (l) + 1)) - 1) << (l)) >> +#define GENMASK(h, l) \ >> + ((~0UL >> (BITS_PER_LONG - ((h) - (l) + 1))) << (l)) >> + >> +#define GENMASK_ULL(h, l) \ >> + ((~0ULL >> (BITS_PER_LONG_LONG - ((h) - (l) + 1))) << (l)) > Slightly bikeshedding here, but may I suggest spelling it > > (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h)))) > > ? This will ensure the arguments are expanded once each, and will, IMHO, > DTRT if/when l > h (namely, yield 0). That's a good point. Peter, what is your view? Kind regards, Maxime > > Rasmus -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Nov 05, 2014 at 04:47:14PM +0100, Maxime Coquelin wrote: > > On 11/05/2014 12:10 PM, Rasmus Villemoes wrote: > >On Tue, Nov 04 2014, Maxime COQUELIN <maxime.coquelin@st.com> wrote: > > > >>-#define GENMASK(h, l) (((U32_C(1) << ((h) - (l) + 1)) - 1) << (l)) > >>-#define GENMASK_ULL(h, l) (((U64_C(1) << ((h) - (l) + 1)) - 1) << (l)) > >>+#define GENMASK(h, l) \ > >>+ ((~0UL >> (BITS_PER_LONG - ((h) - (l) + 1))) << (l)) > >>+ > >>+#define GENMASK_ULL(h, l) \ > >>+ ((~0ULL >> (BITS_PER_LONG_LONG - ((h) - (l) + 1))) << (l)) > >Slightly bikeshedding here, but may I suggest spelling it > > > > (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h)))) > > > >? This will ensure the arguments are expanded once each, and will, IMHO, > >DTRT if/when l > h (namely, yield 0). > That's a good point. > > Peter, what is your view? I'm fine with that, feel free to post another version and I'll replace v3. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 11/05/2014 05:44 PM, Peter Zijlstra wrote: > On Wed, Nov 05, 2014 at 04:47:14PM +0100, Maxime Coquelin wrote: >> On 11/05/2014 12:10 PM, Rasmus Villemoes wrote: >>> On Tue, Nov 04 2014, Maxime COQUELIN <maxime.coquelin@st.com> wrote: >>> >>>> -#define GENMASK(h, l) (((U32_C(1) << ((h) - (l) + 1)) - 1) << (l)) >>>> -#define GENMASK_ULL(h, l) (((U64_C(1) << ((h) - (l) + 1)) - 1) << (l)) >>>> +#define GENMASK(h, l) \ >>>> + ((~0UL >> (BITS_PER_LONG - ((h) - (l) + 1))) << (l)) >>>> + >>>> +#define GENMASK_ULL(h, l) \ >>>> + ((~0ULL >> (BITS_PER_LONG_LONG - ((h) - (l) + 1))) << (l)) >>> Slightly bikeshedding here, but may I suggest spelling it >>> >>> (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h)))) >>> >>> ? This will ensure the arguments are expanded once each, and will, IMHO, >>> DTRT if/when l > h (namely, yield 0). >> That's a good point. >> >> Peter, what is your view? > I'm fine with that, feel free to post another version and I'll replace > v3. Thanks Peter, v4 just sent. Regards, Maxime -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index be5fd38..c2ce66c 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -18,8 +18,11 @@ * position @h. For example * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. */ -#define GENMASK(h, l) (((U32_C(1) << ((h) - (l) + 1)) - 1) << (l)) -#define GENMASK_ULL(h, l) (((U64_C(1) << ((h) - (l) + 1)) - 1) << (l)) +#define GENMASK(h, l) \ + ((~0UL >> (BITS_PER_LONG - ((h) - (l) + 1))) << (l)) + +#define GENMASK_ULL(h, l) \ + ((~0ULL >> (BITS_PER_LONG_LONG - ((h) - (l) + 1))) << (l)) extern unsigned int __sw_hweight8(unsigned int w); extern unsigned int __sw_hweight16(unsigned int w);
On some 32 bits architectures, including x86, GENMASK(31, 0) returns 0 instead of the expected ~0UL. This is the same on some 64 bits architectures with GENMASK_ULL(63, 0). This is due to an overflow in the shift operand, 1 << 32 for GENMASK, 1 << 64 for GENMASK_ULL. Fixes: 10ef6b0dffe404bcc54e94cb2ca1a5b18445a66b Cc: <stable@vger.kernel.org> #v3.13+ Reported-by: Eric Paire <eric.paire@st.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com> --- include/linux/bitops.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)