Re: [PATCH v2] Cygwin: clipboard: Fix a bug in read().

[Thomas Wolff <towo@towo.net>]

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);

Thomas