[PATCH] arm64: fix endianness annotation for __apply_alternatives()/get_alt_insn()
Mark Rutland
mark.rutland at arm.com
Thu Jun 29 07:22:34 PDT 2017
On Thu, Jun 29, 2017 at 03:19:44PM +0100, Will Deacon wrote:
> On Thu, Jun 29, 2017 at 03:13:23PM +0100, Mark Rutland wrote:
> > On Thu, Jun 29, 2017 at 03:26:47PM +0200, Luc Van Oostenryck wrote:
> > > On Thu, Jun 29, 2017 at 11:28:51AM +0100, Will Deacon wrote:
> > > > On Wed, Jun 28, 2017 at 04:55:57PM +0200, Luc Van Oostenryck wrote:
> > > > > get_alt_insn() is used to read and create ARM instructions, which
> > > > > are always stored in memory in little-endian order. These values
> > > > > are thus correctly converted to/from native order when processed
> > > > > but the pointers used to hold the address of these instructions
> > > > > are declared as for native order values.
> > > > >
> > > > > Fix this by declaring the pointers as __le32* instead of u32* and
> > > > > make the few appropriate needed changes.
> > > > >
> > > > > + origptr = (__le32 __force *) ALT_ORIG_PTR(alt);
> > > > > + replptr = (__le32 __force *) ALT_REPL_PTR(alt);
> > > >
> > > > Why is the __force needed here?
> > >
> > > Because of the cast to u32* in:
> > > #define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset)
> > > #define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset)
> > > #define __ALT_PTR(a,f) (u32 *)((void *)&(a)->f + (a)->f)
> > >
> > > Of course, if this (u32*) is not really needed, then the __force
> > > is also not needed.
> > >
> > > And since, it seems indeed to be the case, I'll gladly sent a patch:
> > > -#define __ALT_PTR(a,f) (u32 *)((void *)&(a)->f + (a)->f)
> > > +#define __ALT_PTR(a,f) ((void *)&(a)->f + (a)->f)
> > > if it suits you.
> >
> > Given __ALT_PTR is intended to give a pointer to A64 instructions, which
> > are in le32 format, wouldn't it make more sense for __ALT_PTR to cast to
> > __le32 * ?
>
> Might be a bit weird for ALT_REPL_PTR, which is cast to unsigned long.
Maybe, but that's one cast, rather than two, and matches other similar
casts from a pointer to unsigned long (e.g. the the addr cast in
__range_ok()).
Thanks,
Mark.
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