Sounds good. On Sun, Jul 26, 2015 at 1:24 PM, Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > On 07/24/2015 05:51 PM, Nicholas Miell wrote: >> PTHREAD_PROCESS_SHARED says any thread with access to the memory containing >> the mutex can operate on the mutex and POSIX basically ignores the idea >> that different processes could be running completely incompatible >> executables or whatever. >> >> pthread_mutex_t has a bunch of #ifdefs in the middle of it that change the >> structure size and layout between i386 and x86_64. >> >> Most importantly, the positions of the __nusers and __kind fields are >> swapped (this looks to be an oversight dating back to 2003 when __nusers >> was first introduced and carefully preserved when the separate i386 and >> x86_64 versions of pthreadtypes.h were merged into the single x86 version), >> which means that when the lock and unlock functions attempt to figure out >> what kind of mutex it is (recursive/adaptive/whatever), they'll look at the >> wrong field if the mutex is from the wrong architecture and then things >> will break. >> >> And then there's the fact that the rest of the struct is a union in the >> 32-bit version and flat in the 64-bit version, but that could have been >> worked around if you put a flag in the __kind field that tells the 64-bit >> pthread library that it is looking at a 32-bit mutex. > > Thanks for the additional detail, Nicholas. So, how about a paragraph such > as the following for the manual page: > > POSIX says that any thread in any process with access to the mem‐ > ory containing a process-shared (PTHREAD_PROCESS_SHARED) mutex > can operate on that mutex. However, on 64-bit x86 systems, the > mutex definition for x86-64 is incompatible with the mutex defi‐ > nition for i386, meaning that 32-bit and 64-bit binaries can't > share mutexes on x86-64 systems. > ? > > Cheers, > > Michael > > >> On Fri, Jul 24, 2015 at 12:57 AM, Michael Kerrisk (man-pages) < >> mtk.manpages@xxxxxxxxx> wrote: >> >>> On 03/22/2015 10:38 PM, Nicholas Miell wrote: >>>> On 03/22/2015 07:38 AM, Michael Kerrisk (man-pages) wrote: >>>>> Hello all, >>>>> >>>>> I wrote a short man page documented some of the details of >>>>> NPTL that might affect application developers. Review comments >>>>> would be most welcome. >>>>> >>>>> Thanks, >>>>> >>>>> Michael >>>> >>>> POSIX specifies that process-shared pthread_mutex_t's can be manipulated >>>> by independent processes, however the AMD64 and i386 versions of the >>>> mutex structures are incompatible and cannot be shared. >>>> >>>> This might be true of the other supposedly sharable primitives, I never >>>> bothered to check the rest when I first noticed the problem with mutexes. >>> >>> Nicholas, >>> >>> Can you provide pointers to further information on this topic? >>> >>> Cheers, >>> >>> Michael >>> >>> >>> -- >>> Michael Kerrisk >>> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ >>> Linux/UNIX System Programming Training: http://man7.org/training/ >>> >> > > > -- > 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
