--------- Received message begins Here --------- > > > > Chris Wright wrote: > > > * James Morris (jmorrisat_private) wrote: > > > > > > Ok, this is the same thing I dug up. Register size assignments are > > guaranteed atomic. > > Well praise God for that; I originally wrote my code > assuming that. Greg KH's comment that they _aren't_ > threw me for a loop (although it's very plausible - > so many things ARE different between architectures). > > I'd like to document the assumption ("aligned pointer assignments > are atomic") as a comment in the code, with an > "authoritative as possible" source for this assertion. > Can anyone tell me WHERE they got that information, preferably > a very authoritative source? Or at least, identify platforms > where they can be SURE it's true? > > Conversely, can anyone (ESPECIALLY Greg KH!) tell me any > architecture this assumption is NOT true on, or where I could go > to find such? > > Googling last night didn't really get me anywhere. > I could download every processor and bus spec, but that would > be a multi-year research project :-(. Simple - it isn't true in any arch where the bus size is not equal to the pointer size (usually meaning "bus size is less than pointer size"). The VAX processor had quad sized data transfer, but a 32 bit pointer. Sometimes pointers would get hosed (usually for 64 bit pointer sets). I only read about problems when multiple CPUs were involved with shared memory (yet another size). alignment with one frame (32 bits) would not necessarily be aligned for cache transfer. The bus size on VAX arch varied from 16 bits to 64 bits, depending on the system. I do agree that 99% of the current implementations ARE atomic at the "aligned" 32 bit level. However... newer systems are now doing 64, and 128 bit units, and this introduces potential "nonaligned" transfers that were not anticipated. I do wonder about the PDA bus though (and that IBM wrist watch computer). I don't know of any system where this should be a problem at this time. ------------------------------------------------------------------------- Jesse I Pollard, II Email: pollardat_private Any opinions expressed are solely my own. _______________________________________________ linux-security-module mailing list linux-security-moduleat_private http://mail.wirex.com/mailman/listinfo/linux-security-module
This archive was generated by hypermail 2b30 : Thu Jul 25 2002 - 07:20:56 PDT