scripts/gdb: add container_of helper and convenience function

Provide an internal helper with container_of semantics.  As type lookups
are very slow in gdb-python and we need a type "long" for this, cache the
reference to this type object.  Then export the helper also as a
convenience function form use at the gdb command line.

Signed-off-by: Jan Kiszka <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Jason Wessel <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Ben Widawsky <[email protected]>
Cc: Borislav Petkov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

scripts/gdb/linux/utils.py

@@ -32,3 +32,38 @@ def get_type(self):
             if hasattr(gdb, 'events') and hasattr(gdb.events, 'new_objfile'):
                 gdb.events.new_objfile.connect(self._new_objfile_handler)
         return self._type
+
+
+long_type = CachedType("long")
+
+
+def get_long_type():
+    global long_type
+    return long_type.get_type()
+
+
+def offset_of(typeobj, field):
+    element = gdb.Value(0).cast(typeobj)
+    return int(str(element[field].address).split()[0], 16)
+
+
+def container_of(ptr, typeobj, member):
+    return (ptr.cast(get_long_type()) -
+            offset_of(typeobj, member)).cast(typeobj)
+
+
+class ContainerOf(gdb.Function):
+    """Return pointer to containing data structure.
+
+$container_of(PTR, "TYPE", "ELEMENT"): Given PTR, return a pointer to the
+data structure of the type TYPE in which PTR is the address of ELEMENT.
+Note that TYPE and ELEMENT have to be quoted as strings."""
+
+    def __init__(self):
+        super(ContainerOf, self).__init__("container_of")
+
+    def invoke(self, ptr, typename, elementname):
+        return container_of(ptr, gdb.lookup_type(typename.string()).pointer(),
+                            elementname.string())
+
+ContainerOf()

scripts/gdb/vmlinux-gdb.py

@@ -21,3 +21,5 @@
 except:
     gdb.write("NOTE: gdb 7.2 or later required for Linux helper scripts to "
               "work.\n")
+else:
+    import linux.utils