linprocfs: Fix some bugs in the maps file implementation.

- Export the offset into the backing object, not the object size.
- Fix a bug where we would print the previous entry's "offset" when a
  map_entry has no object.
- Try to identify shared mappings.  Linux prints "s" when the mapping
  "may be shared".  This attempt is not perfect, for example, we print
  "p" for anonymous memory that may be shared via
  minherit(INHERIT_SHARE).

PR:		240992
Reviewed by:	kib
MFC after:	1 week
MFC note:	no OBJ_ANON in stable/12
Differential Revision:	https://reviews.freebsd.org/D23062

1 files changed, 9 insertions, 5 deletions

diff --git a/sys/compat/linprocfs/linprocfs.c b/sys/compat/linprocfs/linprocfs.c
index ab41a5a4d934..caa57f160a2a 100644
--- a/sys/compat/linprocfs/linprocfs.c
+++ b/sys/compat/linprocfs/linprocfs.c
@@ -1146,7 +1146,7 @@ linprocfs_doprocmaps(PFS_FILL_ARGS)
 	vm_map_entry_t entry, tmp_entry;
 	vm_object_t obj, tobj, lobj;
 	vm_offset_t e_start, e_end;
-	vm_ooffset_t off = 0;
+	vm_ooffset_t off;
 	vm_prot_t e_prot;
 	unsigned int last_timestamp;
 	char *name = "", *freename = NULL;
@@ -1156,6 +1156,7 @@ linprocfs_doprocmaps(PFS_FILL_ARGS)
 	int error;
 	struct vnode *vp;
 	struct vattr vat;
+	bool private;
 
 	PROC_LOCK(p);
 	error = p_candebug(td, p);
@@ -1186,17 +1187,20 @@ linprocfs_doprocmaps(PFS_FILL_ARGS)
 		e_start = entry->start;
 		e_end = entry->end;
 		obj = entry->object.vm_object;
-		for (lobj = tobj = obj; tobj; tobj = tobj->backing_object) {
+		off = entry->offset;
+		for (lobj = tobj = obj; tobj != NULL;
+		    lobj = tobj, tobj = tobj->backing_object) {
 			VM_OBJECT_RLOCK(tobj);
+			off += lobj->backing_object_offset;
 			if (lobj != obj)
 				VM_OBJECT_RUNLOCK(lobj);
-			lobj = tobj;
 		}
+		private = (entry->eflags & MAP_ENTRY_COW) != 0 || obj == NULL ||
+		    (obj->flags & OBJ_ANON) != 0;
 		last_timestamp = map->timestamp;
 		vm_map_unlock_read(map);
 		ino = 0;
 		if (lobj) {
-			off = IDX_TO_OFF(lobj->size);
 			vp = vm_object_vnode(lobj);
 			if (vp != NULL)
 				vref(vp);
@@ -1233,7 +1237,7 @@ linprocfs_doprocmaps(PFS_FILL_ARGS)
 		    (e_prot & VM_PROT_READ)?"r":"-",
 		    (e_prot & VM_PROT_WRITE)?"w":"-",
 		    (e_prot & VM_PROT_EXECUTE)?"x":"-",
-		    "p",
+		    private ? "p" : "s",
 		    (u_long)off,
 		    0,
 		    0,