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/
