When run on an nfs filesystem memcheck/tests/pointer-trace fails because it generates warnings  "connection to image failed". This is caused by trying to mmap a deleted file which the nfs file system represents as a (hidden) regular file. This is normally not a problem except when that file is empty.

Fix this by not trying to check whether a file is an ELF or MACHO against an empty (regular) file in di_notify_mmap. And empty file is never a valid ELF or MACHO file (and cannot be represented as DiImage).

diff --git a/coregrind/m_debuginfo/debuginfo.c b/coregrind/m_debuginfo/debuginfo.c
index 97d0f35c0..2e97fca4d 100644
--- a/coregrind/m_debuginfo/debuginfo.c
+++ b/coregrind/m_debuginfo/debuginfo.c
@@ -1216,8 +1216,14 @@ ULong VG_(di_notify_mmap)( Addr a, Bool allow_SkFileV, Int use_fd )
    }
 
    /* Finally, the point of all this stattery: if it's not a regular file,
-      don't try to read debug info from it. */
-   if (! VKI_S_ISREG(statbuf.mode))
+      don't try to read debug info from it. Also if it is a "regular file"
+      but has a zero size then skip it. Having a zero size will definitely
+      fail when trying to create an DiImage and wouldn't be a valid elf or
+      macho file. This can happen when mmapping a deleted file, which
+      would normally fail in the check above, because the stat call will
+      fail.  But if the deleted file is on an NFS file system then a fake
+      (regular) empty file might be returned.  */
+   if (! VKI_S_ISREG(statbuf.mode) || statbuf.size == 0)
       return 0;
 
    /* no uses of statbuf below here. */