> From: Jim Meyering [mailto:j...@meyering.net]
> Sent: Friday, January 08, 2010 12:56 PM
> To: Alain Magloire
> Cc: bug-gzip@gnu.org
> Subject: Re: gzip use of memcpy
>
> Alain Magloire wrote:
> > Bonjour,
>
> Bonjour Alain ! Bonne anneé !
> It's been too long ;-)
>
8-)
Yes, I agree. My best wishes to you also.
> > The behavior of memcpy is well defined:
> >
> > "Copying overlapping buffers isn't guaranteed to work; use memmove() to
> > copy buffers that overlap"
> >
> > In our case for the SH architecture we have a version of memcpy that
> > takes advantage at some specific instruction and above a certain size
> > the copy will be done in reverse (side effect of the optimization).
> >
> > For overlapping copies, the code should be using memmove() as describe
> > in POSIX.
> ...
> > Index: inflate.c
> ...
> > if (w - d >= e)
> > {
> > - memcpy(slide + w, slide + d, e);
> > + memmove(slide + w, slide + d, e);
>
> Can you give sample values of w, d and e for which this change
> makes a difference? Doesn't the preceding (w - d >= e) guard
> ensure that the source and destination buffers never overlap?
>
Correct, I will try to get you the test case. It was from a bad gzip/tar, let
me see if I can get the tester on my team to give me the values, hold on...
> > Index: deflate.c
> ...
> > - memcpy((char*)window, (char*)window+WSIZE, (unsigned)WSIZE);
> > + memmove((char*)window, (char*)window+WSIZE, (unsigned)WSIZE);
>
> The source and destination buffers do not overlap.
You are correct. I have changed it without thinking.
