Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm"

[Josh Poimboeuf]

On Thu, Jul 20, 2017 at 01:01:39PM +0300, Andrey Ryabinin wrote:
> 2017-07-19 20:46 GMT+03:00 Josh Poimboeuf <jpoimboe@xxxxxxxxxx>:
> 
> >
> > After doing some testing, I don't think this approach is going to work
> > after all.  In addition to forcing the stack frame, it also causes GCC
> > to add an unnecessary extra instruction to the epilogue of each affected
> > function:
> >
> >   lea    -0x10(%rbp),%rsp
> >
> > We shouldn't be inserting extra instructions like that.  I also don't
> > think the other suggestion of turning the '__sp' register variable into
> > a global variable is a very good solution either, as that just wastes
> > memory for no reason.
> >
> 
> Wastes memory? How is that wastes memory? That doesn't make any sense.

Yes, you're right, that doesn't make any sense.  I think I was trying to
wrap my head around what it means to have a global register variable --
in a header file no less -- and why clang would treat that differently
than a local register variable.

-- 
Josh