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

[Mark Geisert]

Takashi Yano wrote:
[...]
I think the following patch makes the intent clearer.
What do you think?

 From d0aee9af225384a24ac6301f987ce2e94f262500 Mon Sep 17 00:00:00 2001
From: Takashi Yano <takashi.y...@nifty.ne.jp>
Date: Wed, 8 Dec 2021 17:06:03 +0900
Subject: [PATCH] Cygwin: clipboard: Make intent of the code clearer.

---
  winsup/cygwin/fhandler_clipboard.cc   | 4 ++--
  winsup/cygwin/include/sys/clipboard.h | 1 +
  2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/fhandler_clipboard.cc 
b/winsup/cygwin/fhandler_clipboard.cc
index 05f54ffb3..65a3cad97 100644
--- a/winsup/cygwin/fhandler_clipboard.cc
+++ b/winsup/cygwin/fhandler_clipboard.cc
@@ -76,7 +76,7 @@ fhandler_dev_clipboard::set_clipboard (const void *buf, 
size_t len)
        clipbuf->cb_sec  = clipbuf->ts.tv_sec;
  #endif
        clipbuf->cb_size = len;
-      memcpy (&clipbuf[1], buf, len); // append user-supplied data
+      memcpy (clipbuf->data, buf, len); // append user-supplied data
  
        GlobalUnlock (hmem);
        EmptyClipboard ();
@@ -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, (char *) (clipbuf + 1) + pos, ret);
+         memcpy (ptr, clipbuf->data + pos, ret);
          pos += ret;
        }
      }
diff --git a/winsup/cygwin/include/sys/clipboard.h 
b/winsup/cygwin/include/sys/clipboard.h
index 4c00c8ea1..b2544be85 100644
--- a/winsup/cygwin/include/sys/clipboard.h
+++ b/winsup/cygwin/include/sys/clipboard.h
@@ -44,6 +44,7 @@ typedef struct
      };
    };
    uint64_t      cb_size; // 8 bytes everywhere
+  char          data[];
  } cygcb_t;
  
  #endif

Sigh.  I guess it's not possible to keep rid of a data item like I'd hoped.  At 
least "data[]" is cleaner than the historical "data[1]" here.  If you call the 
item cb_data I can live with it.
Thanks all for the discussion.

..mark