Brian Inglis wrote:
On 2021-12-07 13:18, Thomas Wolff wrote:
Am 07.12.2021 um 15:23 schrieb Corinna Vinschen:
On Dec 7 23:00, Takashi Yano wrote:
- Fix a bug in fhandler_dev_clipboard::read() that the second read
fails with 'Bad address'.
Addresses:
https://cygwin.com/pipermail/cygwin/2021-December/250141.html
---
winsup/cygwin/fhandler_clipboard.cc | 2 +-
winsup/cygwin/release/3.3.4 | 6 ++++++
2 files changed, 7 insertions(+), 1 deletion(-)
create mode 100644 winsup/cygwin/release/3.3.4
diff --git a/winsup/cygwin/fhandler_clipboard.cc
b/winsup/cygwin/fhandler_clipboard.cc
index 0b87dd352..ae10228a7 100644
--- a/winsup/cygwin/fhandler_clipboard.cc
+++ b/winsup/cygwin/fhandler_clipboard.cc
@@ -229,7 +229,7 @@ fhandler_dev_clipboard::read (void *ptr, size_t& len)
if (pos < (off_t) clipbuf->cb_size)
{
ret = (len > (clipbuf->cb_size - pos)) ? clipbuf->cb_size - pos : len;
- memcpy (ptr, &clipbuf[1] + pos , ret);
+ memcpy (ptr, (char *) &clipbuf[1] + pos, ret);
I'm always cringing a bit when I see this kind of expression. Personally
I think (ptr + offset) is easier to read than &ptr[offset], but of course
that's just me. If you agree, would it be ok to change the above to
(char *) (clipbuf + 1)
while you're at it? If you like the ampersand expression more, it's ok,
too, of course. Please push.
In this specific case I think it's actually more confusing because of the type
mangling that's intended in the clipbuf.
At quick glance, it looks a bit as if the following were meant:
(char *) clipbuf + 1
I'd even make it clearer like
+ memcpy (ptr, ((char *) &clipbuf[1]) + pos, ret);
or even
+ memcpy (ptr, ((char *) (&clipbuf[1])) + pos, ret);
If the intent is to address:
clipbuf + pos + 1
use either that or:
&clipbuf[pos + 1]
to avoid obscuring the intent,
and add comments to make it clearer!
Boy am I kicking myself for screwing up the original here and opening this can of
worms. Brian, you'd be correct if clipbuf was (char *) like anything-buf often
is. But here it's a struct defining the initial part of a dynamic char buffer.
So my original
&clipbuf[1]
to mean "just after the defining struct" was OK. But the code needed a ptr to
some char offset after that and
&clipbuf[1] + pos
was wrong. Casting the left term to (char *) would fix it. But I like Corinna's
choice of
(char *) (clipbuf + 1)
to be most elegant and clear of all. Now enclose that in parens and append the
char offset so the new expression is
((char *) (clipbuf + 1)) + pos
and all should be golden. I don't think extra commentary is needed in code.
(I think.)
..mark
