On 08/05/2015 08:23 PM, Rich Felker wrote: > On Wed, Aug 05, 2015 at 11:14:32AM -0700, Nicholas Miell wrote: >> >> >>> On Aug 5, 2015, at 2:36 AM, Torvald Riegel <triegel@xxxxxxxxxx> wrote: >>> >>>> On Tue, 2015-08-04 at 11:50 -0700, Nicholas Miell wrote: >>>>> On Aug 4, 2015, at 8:06 AM, Roland McGrath <roland@xxxxxxxxxxxxx> wrote: >>>>> >>>>> I think we are asserting that they are exactly that by dint of the confstr >>>>> results for _CS_POSIX_V7_ILP32_OFF32_CFLAGS et al. So the question is what >>>>> POSIX actually does or doesn't say about process-shared synchronization >>>>> objects being shared between processes running programs built in different >>>>> POSIX compilation environments. >>>>> >>>>> The other relevant question is whether 32/64 sharing of each particular >>>>> pshared object has in fact worked reliably under glibc in the past. Since >>>>> we haven't been clear and explicit about the subject before AFAIK, then if >>>>> in fact it worked before then people might well have inferred that we made >>>>> such an ABI guarantee. (I hope not, since if so we just broke it.) >>>> >>>> The relevant questions aren't what's the least useful behavior >>>> that POSIX lets us get away with or can we leave it broken >>>> because it never worked;'the questions are what do the other >>>> operating systems do and what do the users want. >>> >>> Those are relevant questions, but they are not the only relevant ones. >>> Some users would also like to share data structures between processes >>> using different glibc builds (eg, different versions), and we won't >>> promise that this works for obvioius reasons. >> >> The reasonable scenario is what we have right now -- 32 and 64-bit >> versions of glibc built from the exact same git commit. And I'd >> exclude static versions of glibc even if they're the same version. > > Why would you exclude static? IMO two static-linked executables using > the same version of glibc should be compatible with each other even if > you don't want to guarantee they'll be compatible with the > same-version shared glibc. > >>> The semaphore example shows that there can be a disadvantage to >>> guaranteeing 32/64b interoperability (specifically, the 64b code is more >>> efficient). For mutex, I *currently* don't see a reason why we couldn't >>> get away with just doing 32b stuff for the pshared case, but there's no >>> guarantee that I can foresee all future needs either. >>> >>> Thus, if we would decide to guarantee 32/64b interoperability, we'd need >>> to have at least strong use cases for that and a decent amount of >>> confidence that making such a guarantee is unlikely to constrain the >>> implementation in the future. >> >> Well, POSIX semaphores are supposed to be a replacement for System V >> semaphores (and this extends to the rest of the POSIX IPC >> primitives); right now they aren't. > > Only for some usage cases. As far as I can tell, POSIX semaphores are > not intended to be required to be implemented as a kernel resource. That last is also true of SysV semaphores, surely? > They don't have permissions enforcement/safety against malicious > processes, (I'm a little lost here. POSIX semaphores do have a permissions mask.) > backout on async process termination, etc. Actually, System V semaphores don't reliably have this either (see BUGS in semop(2)). 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
