> 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. > 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.-- 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
