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

[Paul Eggert <eggert@cs.ucla.edu>]

On 2023-04-20 01:07, Florian Weimer wrote:
> * Paul Eggert:
> 
>>> +extern __typeof (strlcpy) __strlcpy;
>>> +libc_hidden_proto (__strlcpy)
>>> +extern __typeof (strlcat) __strlcat;
>>> +libc_hidden_proto (__strlcat)
>>
>> Glibc shouldn't call these functions internally, so let's not export
>> them to elsewhere in glibc.
> 
> strlcpy looks like it could be called for implementing %s in snprintf.
> That seems like a reasonable optimization.

No, because strlcpy must return the length of the source even when it's 
longer than INT_MAX. (This is a botch in the spec which we apparently 
cannot fix.) So there's no way snprintf could use strlcpy without 
hurting worst-case performance.


> Less sure about strlcat, we could drop the PLT avoidance for that, I
> assume.

Let's drop it for both. If there's ever a real need for either (which I 
doubt) we can add it as needed.


> I expect someone to rewrite this using word-size accesses fairly soon.

That would be headed in the wrong direction. We should not waste time 
trying to optimize these functions' copying actions, as the destinations 
are invariably so small that our attempts to "optimize" will likely hurt 
performance.