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

[Florian Weimer]

* Siddhesh Poyarekar:

>> index 673cfd7272..0c78ad2539 100644
>> --- a/include/string.h
>> +++ b/include/string.h
>> @@ -88,6 +88,10 @@ libc_hidden_proto (__stpcpy)
>>   # define __stpcpy(dest, src) __builtin_stpcpy (dest, src)
>>   #endif
>>   libc_hidden_proto (__stpncpy)
>> +extern __typeof (strlcpy) __strlcpy;
>> +libc_hidden_proto (__strlcpy)
>> +extern __typeof (strlcat) __strlcat;
>> +libc_hidden_proto (__strlcat)
>>   libc_hidden_proto (__rawmemchr)
>>   libc_hidden_proto (__strcasecmp)
>>   libc_hidden_proto (__strcasecmp_l)
>
> Do we want to delay doing this until we have an actual internal use of
> these interfaces?

The *_chk functions need these aliases today.

>> +__fortify_function size_t
>> +__NTH (strlcat (char *__restrict __dest, const char *__restrict __src,
>> +		size_t __n))
>> +{
>> +  if (__glibc_objsize (__dest) != (size_t) -1
>> +      && (!__builtin_constant_p (__n > __glibc_objsize (__dest))
>> +	  || __n > __glibc_objsize (__dest)))
>> +    return __strlcat_chk (__dest, __src, __n, __glibc_objsize (__dest));
>> +  return __strlcat_alias (__dest, __src, __n);
>> +}
>> +#endif /* __USE_MISC */
>> +
>
> Couldn't we use the __glibc_fortify macros here?

Do you have a concrete proposal?  I was just following what we have for
stpncpy and other functions.

I don't think it's possible to use the generic macros for
wcslcpy/wcslcat because of the bytes vs wide characters distinction.

>> +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.

size == 0 is defined in OpenBSD via snprintf equivalence, but maybe
that's over-interpreting the manual page.

Thanks,
Florian