Messages in this thread | | | Date | Sun, 25 Nov 2007 12:16:08 +0100 (CET) | From | Geert Uytterhoeven <> | Subject | Re: [RFC] Documentation about unaligned memory access |
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On Fri, 23 Nov 2007, Heikki Orsila wrote: > On Fri, Nov 23, 2007 at 12:15:53AM +0000, Daniel Drake wrote: > > Why unaligned access is bad > > =========================== > > > > Most architectures are unable to perform unaligned memory accesses. Any > > unaligned access causes a processor exception. > > "Some architectures are unable to perform unaligned memory accesses, > either an exception is generated, or the data > access is silently invalid. In architectures that allow unaligned > access, natural aligned accesses are usually faster than non-aligned." > > > In summary: if your code causes unaligned memory accesses to happen, your code > > will not work on some platforms, and will perform *very* badly on others. > > *very* -> *slower* > > > Natural alignment > > ================= > > Please move this definition before "Why unaligned access is bad". > > Also, it would be nice to have a table of ISAs: > > ISA Need Need > natural alignment > alignment by x > -------------------------------------------- > m68k No 2
`No' for >= 68020. `Yes' for < 68020.
> powerpc/ppc Yes Word size > x86 No No > x86_64 No No
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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