[Qemu-devel] [PATCH] linux-user: fix host_to_target_cmsg in case of multiple headers

["Jonathan Neuschäfer" <j.neuschaefer@gmx.net>]

In the current implementation, __target_cmsg_nxthdr compares a pointer
derived from target_cmsg against the msg_control field of target_msgh
(through subtraction).  This failed for me when emulating i386 code
under x86_64, because pointers in the host address space and pointers in
the guest address space were not the same.  This patch adds a g2h()
address translation around the msg_control value.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
---
 linux-user/syscall_defs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
index edd5f3c..1eaaf2a 100644
--- a/linux-user/syscall_defs.h
+++ b/linux-user/syscall_defs.h
@@ -248,7 +248,7 @@ __target_cmsg_nxthdr (struct target_msghdr *__mhdr, struct target_cmsghdr *__cms
 
   __ptr = (struct target_cmsghdr *)((unsigned char *) __cmsg
                                     + TARGET_CMSG_ALIGN (tswapal(__cmsg->cmsg_len)));
-  if ((unsigned long)((char *)(__ptr+1) - (char *)(size_t)tswapal(__mhdr->msg_control))
+  if ((unsigned long)((char *)(__ptr+1) - (char *)g2h(tswapal(__mhdr->msg_control)))
       > tswapal(__mhdr->msg_controllen))
     /* No more entries.  */
     return (struct target_cmsghdr *)0;
-- 
2.5.0