svn commit: r236026 - in head/sys: amd64/linux32 compat/freebsd32 kern

[Konstantin Belousov]

On Sun, May 27, 2012 at 07:49:36AM +1000, Bruce Evans wrote:
> On Sat, 26 May 2012, Konstantin Belousov wrote:
> 
> >On Sat, May 26, 2012 at 10:21:25PM +1000, Bruce Evans wrote:
> >The 'low level' AKA magic happens in several *_fetch_syscall_args()
> >functions. For both linux32 and freebsd32, the magic code automatically
> >zero-extends the arguments into 64bit entities. Linux passes args in
> >registers, while FreeBSD uses words on stack.
> 
> Actually, the amd64 linux_fetch32_fetch_syscall_args() just copies from
> 64-bit registers frame->tf_r* to 64-bit sa->args[*].  I can't see how
> this gives anything except garbage in the top bits.  Is there magic in
> the switch to 64-bit mode that sets the top bits?  Anyway, sign extension
> would give garbage for unsigned args, and zero-extension would give
> garbage for negative signed args.
Hardware zero-extends any register touched in the 32bit mode.

In fact, please see r217991 for related bug.
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