Re: [PATCH 1/2] Implement strlcpy and strlcat [BZ #178]

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

On 2023-04-06 17:29, Alejandro Colomar wrote:
> Hi Siddhesh,
> 
> On 4/6/23 16:22, Siddhesh Poyarekar wrote:
> [...]
> 
>>> +size_t
>>> +__strlcpy (char *__restrict dest, const char *__restrict src, size_t size)
>>> +{
>>> +  size_t src_length = strlen (src);
>>> +
>>> +  if (__glibc_unlikely (src_length >= size))
>>> +    {
>>> +      if (size > 0)
>>> +	{
>>> +	  /* Copy the leading portion of the string.  The last
>>> +	     character is subsequently overwritten with the NUL
>>> +	     terminator, but the destination size is usually a
>>> +	     multiple of a small power of two, so writing it twice
>>> +	     should be more efficient than copying an odd number of
>>> +	     bytes.  */
>>> +	  memcpy (dest, src, size);
>>> +	  dest[size - 1] = '\0';
>>> +	}
>>> +    }
>>> +  else
>>> +    /* Copy the string and its terminating NUL character.  */
>>> +    memcpy (dest, src, src_length + 1);
>>
>> size == 0 is undefined anyway; we return without touching the dest
>> because that's convenient for us.  OK.
> 
> Is it really convenient?  What real code benefits of that behavior?
> If we remove the conditional it's one less op.

Hmm, and then maybe abort in __strlcpy_chk for size == 0.

Thanks,
Sid