Hello Zack, On 12/16/2015 03:50 PM, Zack Weinberg wrote: > On Wed, Dec 16, 2015 at 9:07 AM, Michael Kerrisk (man-pages) > <mtk.manpages@xxxxxxxxx> wrote: >> >> Yes, but the raw system call can give us EFAULT. That needs to be >> documented. >> >> By the way, what's the reason that one can't tell if it returns >> an error when time() in libc.a is used? > > time() in libc.a assumes that the syscall cannot fail, so it doesn't > set errno. And -EFAULT = (time_t) -14 = 1969-12-31T23:59:46Z is > something that time() could return *without* its being an error. It's > kind of the same problem as strtol() has, except I honestly don't see > any way libc.a could tell the difference. > > Given what other people have said about not changing the kernel-level > behavior, here's a new suggestion for the manpages: > > RETURN VALUE > > Time in seconds since the Epoch. > > ERRORS > > EFAULT `t` is non-NULL and points outside your accessible > address space (but see BUGS). > > On systems where the C library time() wrapper function invokes > an implementation provided by the vdso(7) (so that there is no > trap into the kernel), an invalid address may instead trigger a > SIGSEGV signal. Note that whether vdso(7) is used may depend > on whether a program is statically or dynamically linked. > > BUGS > > Error returns from this system call are indistinguishable from > successful reports that the time is a few seconds _before_ the > Epoch, so the C library never sets `errno` as a result of this call. > > The `t` argument is obsolescent and should always be NULL in > new code. When `t` is NULL, the call cannot fail. Nice! I've added that new text. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
