| Message ID | 1415036398-26984-1-git-send-email-maxime.coquelin@st.com |
|---|---|
| State | New |
| Headers | show |
On Mon, Nov 03, 2014 at 06:39:58PM +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> > Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com> > --- > include/linux/bitops.h | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index be5fd38..81f9725 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -18,8 +18,12 @@ > * 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 - 1) - (h))) & ~((1UL << (l)) - 1)) > + > +#define GENMASK_ULL(h, l) \ > + ((~0ULL >> ((BITS_PER_LONG_LONG - 1) - (h))) & ~((1ULL << (l)) - 1)) > + I was not expecting the mask there, but instead something like: ((~0UL >> (BITS_PER_LONG - (h-l+1))) << l) which shifts the bits to the desired length and then back to the desired place. Would that not be more readable? -- 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
Hi Peter, On 11/04/2014 09:29 AM, Peter Zijlstra wrote: > On Mon, Nov 03, 2014 at 06:39:58PM +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> >> Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com> >> --- >> include/linux/bitops.h | 8 ++++++-- >> 1 file changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/bitops.h b/include/linux/bitops.h >> index be5fd38..81f9725 100644 >> --- a/include/linux/bitops.h >> +++ b/include/linux/bitops.h >> @@ -18,8 +18,12 @@ >> * 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 - 1) - (h))) & ~((1UL << (l)) - 1)) >> + >> +#define GENMASK_ULL(h, l) \ >> + ((~0ULL >> ((BITS_PER_LONG_LONG - 1) - (h))) & ~((1ULL << (l)) - 1)) >> + > I was not expecting the mask there, but instead something like: > > ((~0UL >> (BITS_PER_LONG - (h-l+1))) << l) > > which shifts the bits to the desired length and then back to the desired > place. Would that not be more readable? > Yes, this is indeed more readable. I will send a v2 with your implementation. Thanks, Maxime -- 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
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index be5fd38..81f9725 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -18,8 +18,12 @@ * 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 - 1) - (h))) & ~((1UL << (l)) - 1)) + +#define GENMASK_ULL(h, l) \ + ((~0ULL >> ((BITS_PER_LONG_LONG - 1) - (h))) & ~((1ULL << (l)) - 1)) + 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> Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com> --- include/linux/bitops.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)