[PATCH] ARM: decompressor: clear SCTLR.A bit for v7 cores

Nicolas Pitre
2012-10-11T15:58:15Z

On Thu, 11 Oct 2012, Russell King - ARM Linux wrote:

> On Thu, Oct 11, 2012 at 08:31:47AM -0500, Rob Herring wrote:
> > This only affects v7 cores. It should not vary for v7 cores as unaligned
> > access is a required feature. So how is it going to vary on v7 CPUs?
> > We've got bigger problems if there are v7 cores that don't handle
> > unaligned accesses.
>
> Oh, and this gives me a third reason to NAK this patch. Why only ensure
> that the A bit is clear for v7 CPUs? Why not v6, v5, v4 too? Why does
> ARMv7 get this special treatment?

As I said, gcc knows that ARMv7 can perform word sized accesses even
with misaligned pointers. So when it is passed a pointer marked with
the packed attribute, it will generate a series of byte accesses when
compiling for anything but ARMv7, and use a single ldr or str when
compiling for ARMv7.

Nicolas