Re: [Xen-devel] [PATCH for-4.10] string: fix memmove when size is 0

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Oct 17, 2017 at 07:00:25AM -0600, Jan Beulich wrote:
> >>> On 17.10.17 at 14:52, <roger.pau@xxxxxxxxxx> wrote:
> > On Tue, Oct 17, 2017 at 01:41:35PM +0100, Andrew Cooper wrote:
> >> There are many passed values which could trigger this warning.  Does
> >> 
> >> diff --git a/xen/arch/x86/string.c b/xen/arch/x86/string.c
> >> index cd85a38..4f55856 100644
> >> --- a/xen/arch/x86/string.c
> >> +++ b/xen/arch/x86/string.c
> >> @@ -47,7 +47,7 @@ void *(memmove)(void *dest, const void *src, size_t n)
> >>          "   rep movsb   ; "
> >>          "   cld           "
> >>          : "=&c" (d0), "=&S" (d1), "=&D" (d2)
> >> -        : "0" (n), "1" (n-1+(const char *)src), "2" (n-1+(char *)dest)
> >> +        : "0" (n), "1" ((uintptr_t)src + n - 1), "2" ((uintptr_t)dest + n 
> >> - 1)
> >>          : "memory");
> >>  
> >>      return dest;
> >> 
> >> work any better?
> > 
> > That does indeed work, but I'm not sure if it would mask legitimate
> > pointer overflows by casting them into integers.
> 
> It certainly would, as the tool can't possibly know that the asm()
> itself then effectively casts the integers back to pointers (i.e. it
> has no basis to try to "look through" the cast and continue analysis).

I assume there are no further steps for me, just wait for Julien's
release Ack.

Roger.

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