[PATCH v3 02/13] scripts/gdb: Add container_of helper and convenience function

[Jan Kiszka]

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 <jan.kiszka@xxxxxxxxxxx>
---
 scripts/gdb/utils.py       |   41 +++++++++++++++++++++++++++++++++++++++++
 scripts/gdb/vmlinux-gdb.py |    2 ++
 2 files changed, 43 insertions(+), 0 deletions(-)

diff --git a/scripts/gdb/utils.py b/scripts/gdb/utils.py
index 14e72ec..f97ef79 100644
--- a/scripts/gdb/utils.py
+++ b/scripts/gdb/utils.py
@@ -15,3 +15,44 @@ import gdb
 import re
 
 gdb_version = re.sub("^[^0-9]*", "", gdb.VERSION)
+
+long_type = None
+
+def get_type(type_name):
+	t = gdb.lookup_type(type_name)
+	if t == None:
+		raise gdb.GdbError("cannot resolve type '%s'" % type_name)
+	return t
+
+def get_long_type():
+	global long_type
+	if long_type == None:
+		long_type = get_type("long")
+	return long_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):
+	__doc__ = "Return pointer to containing data structure.\n" \
+		  "\n" \
+		  "$container_of(PTR, \"TYPE\", \"ELEMENT\"): Given PTR, return a pointer to the\n" \
+		  "data structure of the type TYPE in which PTR is the address of ELEMENT.\n" \
+		  "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()
diff --git a/scripts/gdb/vmlinux-gdb.py b/scripts/gdb/vmlinux-gdb.py
index ff75a85..42774d3 100644
--- a/scripts/gdb/vmlinux-gdb.py
+++ b/scripts/gdb/vmlinux-gdb.py
@@ -20,3 +20,5 @@ from utils import gdb_version
 if gdb_version < "7.1":
 	print "NOTE: gdb 7.1 or later required for Linux helper scripts " \
 	      "to work."
+else:
+	import utils
-- 
1.7.3.4

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