Messages in this thread | | | From | "H. Peter Anvin" <> | Date | Sat, 04 Mar 2017 15:03:50 -0800 | Subject | Re: [PATCH 1/3] futex: remove duplicated code |
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<davem@davemloft.net>,Chris Metcalf <cmetcalf@mellanox.com>,Thomas Gleixner <tglx@linutronix.de>,Ingo Molnar <mingo@redhat.com>,Chris Zankel <chris@zankel.net>,Max Filippov <jcmvbkbc@gmail.com>,Arnd Bergmann <arnd@arndb.de>,x86@kernel.org,linux-alpha@vger.kernel.org,linux-snps-arc@lists.infradead.org,linux-arm-kernel@lists.infradead.org,linux-hexagon@vger.kernel.org,linux-ia64@vger.kernel.org,linux-mips@linux-mips.org,openrisc@lists.librecores.org,linux-parisc@vger.kernel.org,linuxppc-dev@lists.ozlabs.org,linux-s390@vger.kernel.org,linux-sh@vger.kernel.org,sparclinux@vger.kernel.org,linux-xtensa@linux-xtensa.org,linux-arch@vger.kernel.org From: hpa@zytor.com Message-ID: <9B46AFA6-C422-41FD-8E8A-356E44A6DCD2@zytor.com>
On March 4, 2017 1:38:05 PM PST, Stafford Horne <shorne@gmail.com> wrote: >On Sat, Mar 04, 2017 at 11:15:17AM -0800, H. Peter Anvin wrote: >> On 03/04/17 05:05, Russell King - ARM Linux wrote: >> >> >> >> +static int futex_atomic_op_inuser(int encoded_op, u32 __user >*uaddr) >> >> +{ >> >> + int op = (encoded_op >> 28) & 7; >> >> + int cmp = (encoded_op >> 24) & 15; >> >> + int oparg = (encoded_op << 8) >> 20; >> >> + int cmparg = (encoded_op << 20) >> 20; >> > >> > Hmm. oparg and cmparg look like they're doing these shifts to get >sign >> > extension of the 12-bit values by assuming that "int" is 32-bit - >> > probably worth a comment, or for safety, they should be "s32" so >it's >> > not dependent on the bit-width of "int". >> > >> >> For readability, perhaps we should make sign- and zero-extension an >> explicit facility? > >There is some of this in already here, 32 and 64 bit versions: > > include/linux/bitops.h > >Do we really need zero extension? It seems the same. > >Example implementation from bitops.h > >static inline __s32 sign_extend32(__u32 value, int index) >{ > __u8 shift = 31 - index; > return (__s32)(value << shift) >> shift; >} > >> /* >> * Truncate an integer x to n bits, using sign- or >> * zero-extension, respectively. >> */ >> static inline __const_func__ s32 sex32(s32 x, int n) >> { >> return (x << (32-n)) >> (32-n); >> } >> >> static inline __const_func__ s64 sex64(s64 x, int n) >> { >> return (x << (64-n)) >> (64-n); >> } >> >> #define sex(x,y) \ >> ((__typeof__(x)) \ >> (((__builtin_constant_p(y) && ((y) <= 32)) || \ >> (sizeof(x) <= sizeof(s32))) \ >> ? sex32((x),(y)) : sex64((x),(y)))) >> >> static inline __const_func__ u32 zex32(u32 x, int n) >> { >> return (x << (32-n)) >> (32-n); >> } >> >> static inline __const_func__ u64 zex64(u64 x, int n) >> { >> return (x << (64-n)) >> (64-n); >> } >> >> #define zex(x,y) \ >> ((__typeof__(x)) \ >> (((__builtin_constant_p(y) && ((y) <= 32)) || \ >> (sizeof(x) <= sizeof(u32))) \ >> ? zex32((x),(y)) : zex64((x),(y)))) >>
Signed versus unsigned... -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
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