Re: [PATCH v4] Implement strlcpy [BZ #178]

[Paul Eggert <eggert at cs dot ucla dot edu>]

On 11/03/2015 08:15 AM, Rich Felker wrote:
> I do think this is
> guaranteed by other implementations, in terms of both actual behavior
> and the implicit requirement not to clobber memory the function is not
> specified to clobber.

I don't see any such implicit requirement, so I agree with Florian here.

My impression all along has been that when a function is given an output 
buffer, it can write whatever it likes to the output buffer, so long as 
the buffer has the proper value when the function returns. In 
particular, the caller can't expect the buffer's irrelevant bytes (i.e., 
bytes not part of the output value) to be preserved. I see nothing in 
POSIX or in the BSD documentation that requires preservation of 
irrelevant bytes, either for strlcpy or for POSIX functions in general.  
So, for example, on POSIX implementations where struct timespec has 
padding bytes, a caller cannot expect clock_gettime(CLOCK_REALTIME, &ts) 
to preserve ts's padding bytes, because POSIX doesn't say irrelevant 
bytes are preserved.

> If there's doubt we should clarify with the authors of the original.

This is not an issue that OpenBSD implementers can unilaterally decide 
now. "Ooops, there's an nonobvious strlcpy feature that we forgot to 
write down, but all implementations are required to support it 
anyway."?!? Sorry, but no. That shouldn't work for clock_gettime, and it 
shouldn't work for strlcpy either.