On 5/20/23 00:21, enh wrote: > On Fri, May 19, 2023 at 1:03 AM Alejandro Colomar > <alx.manpages@xxxxxxxxx> wrote: [...] >> You'll also need to add _Nullable to the function prototypes in the >> SYNOPSIS. > > heh, funnily enough, zijunzhao's adding exactly those annotations to > the bionic headers, which is how we stumbled across this. :) > >> BTW, I see that glibc still requires nonnull in gettimeofday(3). It's >> only settimeofday(3) that is nullable. > > yeah, but the _kernel_ allows null in both (see kernel/time/time.c), > and this is section 2 of the man page. it's unclear to me whether > that's worth calling out up here, or should be down in the > Linux-specific section? (this page seems to be written as if it cares > about Hurd? "On a non-Linux kernel, with glibc ...".) Yes, we care about hurd, and non-g libc, in this page and others. Normally, I would be cautious, and specify the strictest prototype of all implementations about which I care, but in this case, glibc seems unnecessarily restrictive, and I'm ready to add _Nullable if the kernel and some libc support that. However, as a caution, please add a (CAVEATS?) section documenting that glibc doesn't allow NULL there. Or maybe keep the SYNOPSIS without _Nullable, and have some VERSIONS section specifying that other libcs and the kernel support NULL. > >> See: >> >> >> $ grepc gettimeofday /usr/include/*/sys/time.h >> /usr/include/x86_64-linux-gnu/sys/time.h:67: >> extern int gettimeofday (struct timeval *__restrict __tv, >> void *__restrict __tz) __THROW __nonnull ((1)); >> >> >> /usr/include/x86_64-linux-gnu/sys/time.h:75: >> # define gettimeofday __gettimeofday64 >> >> >> $ grepc settimeofday /usr/include/*/sys/time.h >> /usr/include/x86_64-linux-gnu/sys/time.h:86: >> extern int settimeofday (const struct timeval *__tv, >> const struct timezone *__tz) >> __THROW; >> >> >> /usr/include/x86_64-linux-gnu/sys/time.h:106: >> # define settimeofday __settimeofday64 >> >> >> And while NULL may be non-UB, the manual page is not very clear on why >> someone would want to call these functions with NULL. Could you >> please also explain why would someone want to call these functions >> with NULL? (Let's discuss it in the list, and then we see what >> wording we use for the page.) > > so there are definitely several orders of magnitude more users of a > null timezone --- most callers don't want that (not least because > glibc seems to not fill it out anyway? musl certainly doesn't, > implementing gettimeofday() in terms of clock_gettime() instead). > > the users for a null time (and non-null timezone; i haven't seen > anyone -- not even a test -- pass null for both!) are interesting. > Android's init uses settimeofday() with only a timezone, but -- > although the timezone to use is settable in device-specific init > scripts -- for devices in our tree, that's actually always 0. there's > other proprietary (non-Google) code that uses gettimeofday() with only > a timezone, and i'm honestly not sure whether it's deliberate that > it's asking the _kernel_ for the timezone or not (i'm guessing they > want the device timezone rather than the app timezone, but i do not > believe there are devices where the _kernel_ timezone matches the > device timezone?). certainly both of these use cases seem worth > following up on, and i will do. Please. And thanks for the details! > > but looking at musl (which ignores tz in both cases) it seems like the > most impactful change would be to fix "The functions gettimeofday() > and settimeofday() can get and set the time as well as a timezone" :-) :-) Makes sense; although it would be worth being clear about if that's really true, and if libcs do support that as well as the kernel. > > it also seems like an improvement to really call out the libc/kernel > differences more clearly though. Sure. Many pages have a dedicated subsection. Feel free to add it to this page. I'd put it in .SH VERSIONS. $ grep -rn 'C library/kernel differences' man* man2/sigprocmask.2:120:.SS C library/kernel differences man2/setreuid.2:168:.SS C library/kernel differences man2/brk.2:126:.SS C library/kernel differences man2/sigwaitinfo.2:114:.SS C library/kernel differences man2/gethostname.2:122:.SS C library/kernel differences man2/getcpu.2:73:.SS C library/kernel differences man2/fork.2:263:.SS C library/kernel differences man2/epoll_wait.2:258:.SS C library/kernel differences man2/wait4.2:157:.SS C library/kernel differences man2/stat.2:355:.SS C library/kernel differences man2/sigsuspend.2:74:.SS C library/kernel differences man2/access.2:40: /* But see C library/kernel differences, below */ man2/access.2:285:.SS C library/kernel differences man2/clock_getres.2:354:.SS C library/kernel differences man2/getpid.2:57:.SS C library/kernel differences man2/setfsgid.2:57:.SS C library/kernel differences man2/getgroups.2:142:.SS C library/kernel differences man2/sigaction.2:946:.SS C library/kernel differences man2/setresuid.2:100:.SS C library/kernel differences man2/readv.2:290:.SS C library/kernel differences man2/readv.2:342:.SS Historical C library/kernel differences man2/open.2:1393:.SS C library/kernel differences man2/setgid.2:58:.SS C library/kernel differences man2/setfsuid.2:97:.SS C library/kernel differences man2/ptrace.2:2814:.SS C library/kernel differences man2/poll.2:382:.SS C library/kernel differences man2/sigreturn.2:130:.SS C library/kernel differences man2/eventfd.2:267:.SS C library/kernel differences man2/mmap.2:729:.SS C library/kernel differences man2/_exit.2:104:.SS C library/kernel differences man2/time.2:86:.SS C library/kernel differences man2/pread.2:101:.SS C library/kernel differences man2/seccomp.2:975:.IR "C library/kernel differences" . man2/setuid.2:104:.SS C library/kernel differences man2/sched_setaffinity.2:95:return 0 (but see "C library/kernel differences" below, man2/sched_setaffinity.2:220:.SS C library/kernel differences man2/select.2:559:.SS C library/kernel differences man2/sigpending.2:52:.SS C library/kernel differences man2/posix_fadvise.2:135:.SS C library/kernel differences man2/gettimeofday.2:173:.SS C library/kernel differences man2/uname.2:83:.SS C library/kernel differences man2/clone.2:1576:.SS C library/kernel differences man2/getpriority.2:185:.SS C library/kernel differences man2/signalfd.2:331:.SS C library/kernel differences man2/timer_create.2:225:.SS C library/kernel differences man2/wait.2:464:.SS C library/kernel differences man2/nice.2:80:.SS C library/kernel differences man2/chmod.2:303:.SS C library/kernel differences man2/seteuid.2:114:.SS C library/kernel differences man3/getcwd.3:217:.SS C library/kernel differences man3/killpg.3:98:.SS C library/kernel differences man3/mq_notify.3:174:.SS C library/kernel differences man3/mq_open.3:269:.SS C library/kernel differences man3/sigqueue.3:118:.SS C library/kernel differences man3type/epoll_event.3type:37:.SS C library/kernel differences man7/man-pages.7:402:.I "C library/kernel differences" Cheers, Alex > >> Thanks! >> Alex >> >> -- >> <http://www.alejandro-colomar.es/> >> GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5 >> -- <http://www.alejandro-colomar.es/> GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5
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