Re: memcpy(p,p,len)

[Joe Buck <Joe dot Buck at synopsys dot COM>]

On Fri, Apr 30, 2010 at 07:30:33AM -0700, Mark Mielke wrote:
> Just a quick comment than Jan-Benedict's opinion is widely shared by the 
> specification and by the Linux glibc manpage:
> 
> DESCRIPTION
>         The  memcpy()  function  copies  n bytes from memory area src to 
> memory
>         area dest.  The memory areas should not overlap.  Use memmove(3) 
> if the
>         memory areas do overlap.
> 
> It doesn't matter if it sometimes works. Sometimes works programs are 
> sometimes doesn't work programs. :-)

The typical memcpy function will fail for overlapping but unequal memory
ranges, but will work for src == dst.  Switching to memmove would degrade
performance, and that should only be done if there is an actual, rather
than a theoretical bug.  Note that for this use, it's not possible (if
the program is valid) for the ranges to overlap but be unequal.

Another alternative is that instead of using memcpy, a specialized
function could be used that has the required property (the glibc
memcpy does).