lkml.org 
[lkml]   [2019]   [Mar]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 03/20] x86/uaccess: Move copy_user_handle_tail into asm
On Fri, Mar 08, 2019 at 01:53:02PM -0600, Josh Poimboeuf wrote:
> On Fri, Mar 08, 2019 at 08:48:35PM +0100, Peter Zijlstra wrote:
> > On Fri, Mar 08, 2019 at 12:53:21PM -0600, Josh Poimboeuf wrote:
> > > On Thu, Mar 07, 2019 at 12:45:14PM +0100, Peter Zijlstra wrote:
> > > > /*
> > > > + * Try to copy last bytes and clear the rest if needed.
> > > > + * Since protection fault in copy_from/to_user is not a normal situation,
> > > > + * it is not necessary to optimize tail handling.
> > > > + *
> > > > + * Input:
> > > > + * rdi destination
> > > > + * rsi source
> > > > + * rdx count
> > > > + *
> > > > + * Output:
> > > > + * eax uncopied bytes or 0 if successful.
> > > > + */
> > > > +ALIGN;
> > > > +copy_user_handle_tail:
> > > > + movl %edx,%ecx
> > > > +1: rep movsb
> > > > +2: mov %ecx,%eax
> > > > + ASM_CLAC
> > > > + ret
> > > > +
> > > > + _ASM_EXTABLE_UA(1b, 2b)
> > > > +ENDPROC(copy_user_handle_tail)
> > >
> > > This is an unstructured piece of code rather than a callable function,
> > > END would probably be more appropriate. Or maybe it should just be a
> > > local label (.Lcopy_user_handle_tail) because I don't think the
> > > alignment and ELF symbol size are even needed.
> >
> > ENDPROC makes it STT_FUNC and gets us stricter AC tests.
>
> How so? I would have thought the opposite. Doesn't objtool only follow
> a jump if its destination is to a non-function? Otherwise it's
> considered a sibling call.

Normally yes, but we don't do that for .fixup I think. And by setting
STT_FUNC we enable the 'redundant CLAC' warning, which is ignored for
!STT_FUNC.

\
 
 \ /
  Last update: 2019-03-10 14:23    [W:0.071 / U:3.344 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site