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SubjectRe: [PATCH v2 02/36] x86/uaccess: __chk_range_not_ok is unlikely to return true

* Borislav Petkov <bp@alien8.de> wrote:

> On Mon, Oct 05, 2015 at 05:47:50PM -0700, Andy Lutomirski wrote:
> > This should improve code quality a bit. It also shrinks the kernel
> > text.
> >
> > Before:
> > text data bss dec hex filename
> > 21828379 5194760 1277952 28301091 1afd723 vmlinux
> > text data bss dec hex filename
> > 21827997 5194760 1277952 28300709 1afd5a5 vmlinux
> >
> > Signed-off-by: Andy Lutomirski <luto@kernel.org>
> > ---
> > arch/x86/include/asm/uaccess.h | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> > index 3e911c68876e..09b1b0ab94b7 100644
> > --- a/arch/x86/include/asm/uaccess.h
> > +++ b/arch/x86/include/asm/uaccess.h
> > @@ -51,13 +51,13 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
> > * limit, not add it to the address).
> > */
> > if (__builtin_constant_p(size))
> > - return addr > limit - size;
> > + return unlikely(addr > limit - size);
> >
> > /* Arbitrary sizes? Be careful about overflow */
> > addr += size;
> > - if (addr < size)
> > + if (unlikely(addr < size))
> > return true;
> > - return addr > limit;
> > + return unlikely(addr > limit);
>
> It certainly uglifies it though. Are the wins worth the (un-)readability
> hit?

Well, adding likely/unlikely hints in headers is OK I think, especially since
these are performance sensitive user-access routines.

Thanks,

Ingo


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