On Mon, Aug 22, 2016 at 02:49:07AM +1000, Bruce Evans wrote: > On Sun, 21 Aug 2016, Slawa Olhovchenkov wrote: > > > On Sun, Aug 21, 2016 at 11:39:02PM +1000, Bruce Evans wrote: > > > >> On Sun, 21 Aug 2016, Slawa Olhovchenkov wrote: > >>> I am remeber about platforms with missaligment trap when > >>> accessing int16 by odd address. Now platforms like this do not exist > >>> anymore? > >> > >> i386 still exists, and it supports trapping on misalignement for at least > >> CPL 3 (not kernel CPL 0). IIRC, amd64 drops support for this. > > > > Someone enable and support this? I am don't see. > > May be PPC trap on this? > > Alpha trap on this, but support of Alpha is droped. > > It is a 1-line change in asm (or a little more in C with #includes) to > enable the trap:
OK, we can turn amd64 in this mode. And cat do request to kernel with unalligned access, this cause trap and panic, yes? > It is a trillion-line change to fix the compilers and applications to not > do misaligned accesses :-). I only tried to use this ~25 years ago. Then > the most obvious compiler bug was generating 32-bit acccesses to assign > large but misaligned structs. If the compiler just generated calls to > memcpy(), that might work, but in practice libraries also assume alignment. This issuse can be trigerred and by two-bytes assigmen, yes? > >>>> There are also endianness problems. The old version was even more broken > >>>> on big endian systems. The current version needs some magic to reverse > >>>> the memcpy() of the bits. We already depend on this for some 64-bit > >>>> syscalls like lseek(). > >>> > >>> Can you explain some more? > >>> This is not transfer over network and don't read from external media. > >>> Where is problem? > >> > >> It is similar to a network transfer. It needs a protocol to pass values > >> to applications. Type puns are fragile even within a single compilation > >> unit. > > > > Application ad kernel run with same byte order, not? > > The application can do anything it wants, but has to translate if it uses > the kernel or a library written in another language. You talk about different byte order in differenr languages? _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
