Re: [Qemu-devel] [libfdt][PATCH v2] implement strnlen for systems that need it

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Tue, Oct 24, 2017 at 12:16:47AM -0400, Programmingkid wrote:
> 
> > On Oct 22, 2017, at 1:33 AM, David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org> wrote:
> > 
> > On Fri, Oct 20, 2017 at 04:44:58PM -0700, Richard Henderson wrote:
> >> On 10/20/2017 10:55 AM, John Arbuckle wrote:
> >>> +static inline size_t strnlen(const char *string, size_t max_count)
> >>> +{
> >>> +    size_t count;
> >>> +    for (count = 0; count < max_count; count++) {
> >>> +        if (string[count] == '\0') {
> >>> +            break;
> >>> +        }
> >>> +    }
> >>> +    return count;
> >> 
> >> Not to nitpick, but
> >> 
> >>  const char *p = memchr(string, 0, max_count);
> >>  return p ? max_count : p - string;
> > 
> > Richard's right, that's definitely a better implementation.
> 
> I was just wondering, what if we rewrote the code to use strlen()
> instead of strnlen(). Would that be an acceptable solution?

Only if you can do so safely - i.e. without accessing memory beyond
what we're supposed to.  I don't think you'll be able to do that
without effectively re-implementing strnlen(), there's a reason I used
it in the first place, after all.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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