[PATCH v4 03/13] scripts/gdb: Add lx-symbols command

[Jan Kiszka]

This is probably the most useful helper when debugging kernel modules:
lx-symbols will first reload vmlinux. Then it searches recursively for
*.ko files in the specified paths and the current directory. Finally it
walks the kernel's module list, issuing the necessary add-symbol-file
command for each loaded module so that gdb know which module symbol
correspond to which address.

In addition, the command installs a silent breakpoint in the load_module
function at the point where the module was loaded but not yet
initialized. The breakpoint handler will try to load symbols from the
module files found during lx-symbols execution. This way, breakpoints
can be set to module initialization functions, and there is usually no
need to explicitly call lx-symbols after (re-)loading a module.

Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
---
 scripts/gdb/symbols.py     |  153 ++++++++++++++++++++++++++++++++++++++++++++
 scripts/gdb/vmlinux-gdb.py |    1 +
 2 files changed, 154 insertions(+), 0 deletions(-)
 create mode 100644 scripts/gdb/symbols.py

diff --git a/scripts/gdb/symbols.py b/scripts/gdb/symbols.py
new file mode 100644
index 0000000..c50d5e1
--- /dev/null
+++ b/scripts/gdb/symbols.py
@@ -0,0 +1,153 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  load kernel and module symbols
+#
+# Copyright (c) Siemens AG, 2011-2013
+#
+# Authors:
+#  Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+import os
+import re
+import string
+
+from utils import *
+
+class LinuxSymbols(gdb.Command):
+	__doc__ = "(Re-)load symbols of Linux kernel and currently loaded modules.\n" \
+		  "\n" \
+		  "The kernel (vmlinux) is taken from the current working directly. Modules (.ko)\n" \
+		  "are scanned recursively, starting in the same directory. Optionally, the module\n" \
+		  "search path can be extended by a space separated list of paths passed to the\n" \
+		  "lx-symbols command."
+
+	module_files = []
+	breakpoint = None
+
+	def __init__(self):
+		super(LinuxSymbols, self).__init__("lx-symbols",
+						   gdb.COMMAND_FILES,
+						   gdb.COMPLETE_FILENAME)
+
+	def _load_module_symbols(self, module):
+		module_name = module['name'].string()
+		module_addr = str(module['module_core']).split()[0]
+		module_pattern = ".*/" + \
+			string.replace(module_name, "_", r"[_\-]") + r"\.ko$"
+		module_path = ""
+		for name in self.module_files:
+			if re.match(module_pattern, name):
+				module_path = name
+				break
+
+		if module_path:
+			print "loading @" + module_addr + ": " + module_path
+			if gdb.VERSION >= "7.2":
+				gdb.execute("add-symbol-file " + \
+					    module_path + " " + module_addr,
+					    to_string = True)
+			else:
+				gdb.execute("add-symbol-file " + \
+					    module_path + " " + module_addr)
+		else:
+			print "no module object found for '" + \
+			      module_name + "'"
+
+	if gdb_version >= "7.3":
+		class _LoadModuleBreakpoint(gdb.Breakpoint):
+			def __init__(self, spec, gdb_command):
+				super(LinuxSymbols._LoadModuleBreakpoint,
+				      self).__init__(spec, internal = True)
+				self.silent = True
+				self.gdb_command = gdb_command
+
+			def stop(self):
+				module = gdb.parse_and_eval("mod")
+				self.gdb_command._load_module_symbols(module)
+				return False
+
+		def _find_breakpoint_location(self):
+			breakpoint_match = "^[0-9]*[\t]*err = parse_args\(.*"
+
+			src = gdb.execute("list kernel/module.c:load_module",
+					  to_string = True)
+			done = False
+			lineno = None
+			while not done:
+				src = gdb.execute("list", to_string = True)
+				for line in src.splitlines():
+					if re.match(breakpoint_match, line):
+						done = True
+						lineno = line.split()[0]
+						break
+					elif re.match("^[0-9]*\t}$", line):
+						done = True
+						break
+			return lineno
+
+	def _load_all_module_symbols(self, arg):
+		modules = gdb.parse_and_eval("modules")
+		entry = modules['next']
+		if entry == modules.address:
+			print "no modules found"
+			return
+
+		self.module_files = []
+		paths = arg.split()
+		paths.append(os.getcwd())
+		for path in paths:
+			print "scanning for modules in " + path
+			for root, dirs, files in os.walk(path):
+				for name in files:
+					if re.match(r".*\.ko$", name):
+						self.module_files.append(
+							root + "/" + name)
+
+		module_type = gdb.lookup_type("struct module").pointer()
+
+		while entry != modules.address:
+			module = container_of(entry, module_type, "list")
+			self._load_module_symbols(module)
+			entry = entry['next']
+
+	def invoke(self, arg, from_tty):
+		print "loading vmlinux"
+
+		saved_states = []
+		if (gdb.breakpoints() != None):
+			for breakpoint in gdb.breakpoints():
+				saved_states.append({
+					'breakpoint': breakpoint,
+					'enabled': breakpoint.enabled })
+
+		# drop all current symbols and reload vmlinux
+		gdb.execute("symbol-file", to_string = True)
+		gdb.execute("symbol-file vmlinux")
+
+		self._load_all_module_symbols(arg)
+
+		for saved_state in saved_states:
+			saved_state['breakpoint'].enabled = \
+				saved_state['enabled']
+
+		if gdb_version < "7.3":
+			print "Note: symbol update on module loading not " \
+			      "supported with this gdb version"
+		else:
+			if self.breakpoint != None:
+				self.breakpoint.delete()
+				self.breakpoint = None
+			lineno = self._find_breakpoint_location()
+			if lineno != None:
+				self.breakpoint = self._LoadModuleBreakpoint(
+					lineno, self)
+			else:
+				print "unable to detect breakpoint location " \
+				      "of load module completion"
+
+LinuxSymbols()
diff --git a/scripts/gdb/vmlinux-gdb.py b/scripts/gdb/vmlinux-gdb.py
index 8ef76c9..3553b7d 100644
--- a/scripts/gdb/vmlinux-gdb.py
+++ b/scripts/gdb/vmlinux-gdb.py
@@ -22,3 +22,4 @@ if gdb_version < "7.1":
 	      "to work."
 else:
 	import utils
+	import symbols
-- 
1.7.3.4

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