strncmp issue

[Olivier Houchard]

On Tue, Apr 28, 2009 at 08:42:07AM -0600, M. Warner Losh wrote:
> In message: <1240918262.85945.1.camel at buffy.york.ac.uk>
>             Gavin Atkinson <gavin at freebsd.org> writes:
> : 
> : This probably belongs on the -arm list, which I'm CCing.
> : 
> : On Tue, 2009-04-28 at 15:22 +0530, Channa wrote:
> : > Hi,
> : > 
> : > I am using the freebsd implementation of strncmp for ARM which is an
> : > assembly implementation.
> : > I have a small doubt, when i tested the strncmp by passing the third argument:
> : > 'n' as -1 the return values is  '0' instead it should '-1'.
> : > When the third argument  to strncmp is as below:
> : > 
> : > ret = strncmp("a","b",-1)
> 
> This is the same as strncnp("a", "b", UMAXINT) because the len
> argument is "size_t" which is unsigned.
> 
> : > I think the assembly implementation in
> : > src/lib/libc/arm/string/strncmp.S file needs
> : > to be modified to take care of the above condition.
> : > 
> : > In the current implementation
> : > /* if ((len - 1) < 0) return 0 */
> : >         subs    r2, r2, #1
> : >         movmi   r0, #0
> : >         RETc(mi)
> : > 
> : > This should be changed to check as below
> : > 
> : > /* if ((len ) < 0) return 0 */
> : > /* Assembly code here */
> : > 
> : > Could anyone help in solving the above issue.?
> 
> This is a bug in your code not in strncmp.
> 
> Warner
> 
> 

Still, strncmp("a", "b", UMAXINT) should not return 0, so if it does, it's
a bug.

Olivier