From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 0/9] posix_clocks: Prepare syscalls for 64 bit time_t conversion Date: Fri, 17 Nov 2017 11:30:57 +0100 Message-ID: References: <20171110224259.15930-1-deepa.kernel@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: Sender: linux-arch-owner@vger.kernel.org To: Thomas Gleixner Cc: Deepa Dinamani , John Stultz , Linux Kernel Mailing List , y2038 Mailman List , Arnaldo Carvalho de Melo , Benjamin Herrenschmidt , Christian Borntraeger , Catalin Marinas , Chris Metcalf , cohuck@redhat.com, David Miller , Helge Deller , devel@driverdev.osuosl.org, gerald.schaefer@de.ibm.com, gregkh , Heiko Carstens , Jan Hoeppner , "H. Peter Anvin" , "James E.J. Bottomley" , Julian List-Id: linux-api@vger.kernel.org On Fri, Nov 17, 2017 at 10:54 AM, Thomas Gleixner wrote: > On Fri, 17 Nov 2017, Arnd Bergmann wrote: >> On Fri, Nov 17, 2017 at 9:58 AM, Thomas Gleixner wrote: >> >> No, syscall that existing 32-bit user space enters would be handled by >> compat_sys_nanosleep() on both 32-bit and 64-bit kernels at that >> point. The idea here is to make the code path more uniform between >> 32-bit and 64-bit kernels. > > So on a 32bit system compat_sys_nanosleep() would be the legacy > sys_nanosleep() with the existing syscall number, but you don't want to > introduce a new sys_nanosleep64() for 32bit. That makes a lot of sense. > > So back to your original question whether to use #if (MAGIC logic) or a > separate config symbol. Please use the latter, these magic logic constructs > are harder to read and prone to get wrong at some point. Having the > decision logic in one place is always the right thing to do. How about this: config LEGACY_TIME_SYSCALLS def_bool 64BIT || !64BIT_TIME help This controls the compilation of the following system calls: time, stime, gettimeofday, settimeofday, adjtimex, nanosleep, alarm, getitimer, setitimer, select, utime, utimes, futimesat, and {old,new}{l,f,}stat{,64}. These all pass 32-bit time_t arguments on 32-bit architectures and are replaced by other interfaces (e.g. posix timers and clocks, statx). C libraries implementing 64-bit time_t in 32-bit architectures have to implement the handles by wrapping around the newer interfaces. New architectures should not explicitly disable this. Arnd