slotmem handles this well, afaict ;) On Aug 13, 2012, at 12:32 PM, Jeff Trawick <traw...@gmail.com> wrote:
> On Mon, Aug 13, 2012 at 12:30 PM, Rainer Jung <rainer.j...@kippdata.de> wrote: >> Hi, >> >> PR 53040 reveals, that mod_socache_shmcb has an alignment problem. One of >> the three structs mapped into shm contains an apr_time_t member, which at >> least on Sparc is 8 Bytes, whereas for 32 bit builds long is only 4 Bytes. >> >> Currently everything is aligned for 4 Bytes, so we get bus errors/crashes >> when trying to assign the apr_time_t to an address that is only divisible by >> 4 instead of 8. >> >> I can easily reproduce the problem. >> >> A possible solution is to pad the three structures SHMCBHeader, >> SHMCBSubcache and SHMCBIndex to a multiple of 8 Bytes length. For Subcache >> and Index this is already true by coincidence, SHMCBHeader needs another 4 >> Bytes. >> >> I wonder what the right solution is. In the patch >> >> http://people.apache.org/~rjung/patches/mod_socache_shmcb-padding.patch >> >> I hard coded the padding, but I don't really like it, because it breaks if >> members are added to the struct. I could add a sizeof() test during startup >> or probably even compilation to warn or err, if the padding is wrong. >> >> I see several recipes for alignment using pragmas and attribute, but all of >> them are compiler specific. >> >> One could also wrap the struct in a wrapped struct, so that one could use >> the sizeof() of the inner struct to determine the padding of the outer >> struct. That would make the code convoluted. >> >> I checked other parts of the code, but couldn't find a simple solution. Any >> hints how to do this nicely? > > APR_ALIGN_DEFAULT? > >> >> Regards, >> >> Rainer > > > > -- > Born in Roswell... married an alien... > http://emptyhammock.com/ >
