On Thu, 3 Aug 2023 23:30:31 +0900
Rin Okuyama <rokuyama...@gmail.com> wrote:
> On 2023/08/03 23:23, Valery Ushakov wrote:
> > On Thu, Aug 03, 2023 at 13:33:27 +0000, Rin Okuyama wrote:
> >
> >> -Wuse-after-free for GCC 12 is premature. It fires on a common idiom:
> >>
> >> newbuf = realloc(buf, size);
> >> p = newbuf + (p - buf);
> >>
> >> Let shut this up for GCC 12 (with hoping it gets improved for 13!).
> >
> > C99 says
> >
> > J.2 Undefined behavior
> >
> > [#1] The behavior is undefined in the following
> > circumstances:
> > [...]
> > -- The value of a pointer to an object whose lifetime has
> > ended is used (6.2.4).
> >
> >
> > Yes, for the "obvious" implementation of pointers as addresses the
> > above idiom happens to work, but it doesn't make that idiom any less
> > UB.
>
> Ah, I only thought about "obvious" impl. Thank you for kind
> explanation! I will revert them for now.
Hi,
Is this sort of fix acceptable for the above cases?
-Tobias
RCS file: /cvsroot/src/usr.bin/sort/files.c,v
retrieving revision 1.42
diff -p -u -r1.42 files.c
--- files.c 5 Aug 2015 07:10:03 -0000 1.42
+++ files.c 7 Aug 2023 21:53:45 -0000
@@ -199,13 +199,14 @@ seq(FILE *fp, u_char **line)
/* Long line - double size of buffer */
/* XXX: Check here for stupidly long lines */
buf_size *= 2;
+ ptrdiff_t offset = pos - buf;
new_buf = realloc(buf, buf_size);
if (!new_buf)
err(2, "realloc of linebuf to %zu bytes failed",
buf_size);
-
+
end = new_buf + buf_size;
- pos = new_buf + (pos - buf);
+ pos = new_buf + offset;
buf = new_buf;
}
}
