I'm confused between the (1) and (2) choices, and can't see where bumping the message size fits.
Nonetheless, I think bumping the size, fixing the alignment issues, and bumping the ABI version is the best solution here. On Fri, Aug 26, 2016 at 12:33 PM, Luca Boccassi <[email protected]> wrote: > I've given some more thoughts and testing to the alignment issue. I can > reproduce the problem by enabling alignment checks on x86 too. > > But most importantly, I think we cannot get away from bumping the ABI > with this fix, however we rearrange it, simply because applications need > to be rebuilt against the new header to be fixed. A simple rebuild of > the libzmq.so is not enough. And the way to do this is to bump the ABI > so that distros can schedule transitions and rebuilds and so on. > > So the choice list is now restricted to: > > 1) Bump ABI > 2) Revert the fix and leave everything broken on sparc64 and some > aarch64 (rpi3 seems not to be affected, must depend on the SoC flavour) > > If we go with 2, we might as well get 2 birds with one stone and bump > the zmq_msg_t size to 128 as we have talked about in the past. > > Doron, this would help with the new UDP based socket types right? > > Pros of bumping msg size: > > - we can get rid of the malloc() in the lmsg type case as all the data > will fit > > Cons: > > - for the vsm/cmsg type cases (for most architectures anyway) it won't > fit anymore into a single cacheline > > Given all this, I'd say we should go for it. > > Opinions? > > On Sat, 2016-08-13 at 16:59 +0100, Luca Boccassi wrote: >> Hello, >> >> Trying to give some thoughts again on the libzmq 4.2 release. It's >> really long overdue! >> >> The main issue from my point of view is this change: >> >> https://github.com/zeromq/libzmq/commit/d9fb1d36ff2008966af538f722a1f4ab158dbf64 >> >> -typedef struct zmq_msg_t {unsigned char _ [64];} zmq_msg_t; >> +/* union here ensures correct alignment on architectures that require >> it, e.g. >> + * SPARC >> + */ >> +typedef union zmq_msg_t {unsigned char _ [64]; void *p; } zmq_msg_t; >> >> >> This is flagged by the common ABI checkers tools as an ABI breakage >> (see: http://abi-laboratory.pro/tracker/timeline/zeromq/ ). And it makes >> sense from this point of view: if some applications on some >> architectures are broken due to wrong alignment, they would need to be >> rebuilt, and the way to ensure that is to bump the ABI "current" digit >> to make sure maintainers do a rebuild. >> >> On the other hand, signaling an ABI breakage is a pain, and a cause of >> major churn for packagers and maintainers. It means for example a new >> package has to be created (eg: libzmq5 -> libzmq6), and a transition has >> to be started and all reverse dependencies need to be rebuilt. And if >> this is pointless for all save a few corner cases (eg SPARC64 as for >> above) it's all quite frustrating. >> >> So we have a choice to make before we release 4.2, four possibilities as >> far as I can see: >> >> 1) Ignore the ABI checkers and get yelled at by maintainers and >> packagers. Also the SPARC64 users will most likely NOT get their bug >> fixed >> 2) Bump ABI revision to 6 and get yelled at by maintainers and packagers >> 3) Revert the above change and postpone it to when we have a more >> generally useful reason to break ABI (bump zmq_msg_t from 64 to 128 >> bytes for example, Doron?) >> 4) Try to be clever and revert the above change and use something like >> #pragma pack(8). This will fool the ABI checkers (I tried it), and given >> that typedef is only used externally to allocate the right size it >> shouldn't actually affect anything, apart from the users of SPARC64 >> which should get the bugfix with this too. This is very sneaky :-) >> >> CC'ing Lazslo, the Debian maintainer, given what we choose to do might >> result in a lot of work for him :-) >> >> Opinions? >> >> Kind regards, >> Luca Boccassi >> >> On Tue, 2016-05-03 at 10:39 +0200, Pieter Hintjens wrote: >> > Hi all, >> > >> > I'm just throwing some ideas on the table. We have a good package of >> > work on master and it's probably time to make a 4.2 release. >> > >> > Luca has already back-ported the enable/disable draft design from >> > zproject (CZMQ et al). Yay! So we can now release stable master >> > safely, while continuing to refine and extend the draft API sections. >> > >> > I propose: >> > >> > - to end with the stable fork policy; this was needed years ago when >> > we had massively unstable masters. It's no longer a problem. >> > - to use the github release function for libzmq releases and deprecate >> > the separate delivery of tarballs. >> > - we aim to make a 4.2.0 rc asap, then fix any issues we get, with >> > patch releases as usual. >> > - we backport the release function to older maintained releases (4.1, >> > 3.2) so that their tarballs are provided by github instead of >> > downloads.zeromq.org. >> > >> > Problems: >> > >> > - this will break a few things that depend on downloads.zeromq.org. To >> > be fixed as we go. >> > - github tarballs are not identical to source tarballs, particularly >> > they lack `configure`. I propose changing our autotools build >> > instructions so they always start with `./autogen,sh` no matter where >> > the sources come from. >> > >> > I think this will work and also let us gracefully deprecate/switch off >> > the downloads box. >> > >> > -Pieter >> > _______________________________________________ >> > zeromq-dev mailing list >> > [email protected] >> > http://lists.zeromq.org/mailman/listinfo/zeromq-dev >> >> > > > > _______________________________________________ > zeromq-dev mailing list > [email protected] > http://lists.zeromq.org/mailman/listinfo/zeromq-dev _______________________________________________ zeromq-dev mailing list [email protected] http://lists.zeromq.org/mailman/listinfo/zeromq-dev
