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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.10.17 at 12:44, <roger.pau@xxxxxxxxxx> wrote:
> 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.

Plus, considering his earlier comments, preferably a "not-a-nack"
clarification by Andrew.

Jan


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