A script that used by GDB to load the symbols from Linux kernel modules

[Hui Zhu]

Hi,

When use GDB to debug or trace your kernel with KGDB, QEMU debug
interface or KGTP.  You must get some trouble with LKM symbols.  For
example:
(gdb) target remote localhost:12345
Remote debugging using localhost:12345
native_safe_halt () at
/home/teawater/big/kernel/linux-2.6/arch/x86/include/asm/irqflags.h:50
50	}
(gdb) b e100_poll
Function "e100_poll" not defined.
Make breakpoint pending on future shared library load? (y or [n])
This is because GDB didn't get the LKM symbols.  You can do it with
your hand.  But if you have a lot of LKMs, it will need some time.

Now, GDB support python script.  The attachment is a script to load
all symbols from Linux kernel modules to GDB.
For example:
(gdb) target remote localhost:12345
Remote debugging using localhost:12345
native_safe_halt () at
/home/teawater/big/kernel/linux-2.6/arch/x86/include/asm/irqflags.h:50
50	}
(gdb) so ~/kernel/svn/branches/teawater/getmod.py
(gdb) b e100_poll
Breakpoint 1 at 0xc889db40: file
/home/teawater/big/kernel/linux-2.6/drivers/net/e100.c, line 2165.

This script will include in KGTP(https://code.google.com/p/kgtp/) source.

Thanks,
Hui
#!/usr/bin/python

# This script is used by GDB to load the symbols from Linux kernel modules
# GPL
# Copyright(C) Hui Zhu (teawater@xxxxxxxxx), 2011

#Set special mod_search_dir
#set $mod_search_dir="dir"
#Clear special mod_search_dir
#set $mod_search_dir=(void)1

import gdb;
import os;

def format_file(name):
	tmp = "";
	for c in name:
		if c == "_":
			c = "-";
		tmp += c;
	return tmp;

#Get the mod_search_dir
mod_search_dir = gdb.parse_and_eval("$mod_search_dir");
if mod_search_dir.type.code == gdb.TYPE_CODE_ARRAY:
	mod_search_dir = str(mod_search_dir);
	mod_search_dir = mod_search_dir[1:len(mod_search_dir)];
	mod_search_dir = mod_search_dir[0:mod_name.index("\"")];
else:
	mod_search_dir = str(gdb.execute("info files", False, True));
	mod_search_dir = mod_search_dir[mod_search_dir.index("Symbols from \"")+len("Symbols from \""):len(mod_search_dir)];
	mod_search_dir = mod_search_dir[0:mod_search_dir.index("\"")];
	mod_search_dir = mod_search_dir[0:mod_search_dir.rindex("/")];
print "Search modules from "+mod_search_dir+"\n";

mod_list_offset = long(gdb.parse_and_eval("((size_t) &(((struct module *)0)->list))"));
mod_list = long(gdb.parse_and_eval("(&modules)"));
mod_list_current = mod_list;

while 1:
	mod_list_current = long(gdb.parse_and_eval("((struct list_head *) "+str(mod_list_current)+")->next"));

	#check if need break the loop
	if mod_list == mod_list_current:
		break;

	mod = mod_list_current - mod_list_offset;

	#get mod_name
	mod_name = str(gdb.parse_and_eval("((struct module *)"+str(mod)+")->name"));
	mod_name = mod_name[mod_name.index("\"")+1:len(mod_name)];
	mod_name = mod_name[0:mod_name.index("\"")];
	mod_name += ".ko"
	mod_name = format_file(mod_name);

	#get mod_dir_name
	mod_dir_name = "";
	for root, dirs, files in os.walk(mod_search_dir):
		for afile in files:
			tmp_file = format_file(afile);
			if tmp_file == mod_name:
				mod_dir_name = os.path.join(root,afile);
				break;
		if mod_dir_name != "":
			break;

	command = " ";

	#Add module_core to command
	command += str(gdb.parse_and_eval("((struct module *)"+str(mod)+")->module_core"));

	#Add each sect_attrs->attrs to command
	#get nsections
	nsections = int(gdb.parse_and_eval("((struct module *)"+str(mod)+")->sect_attrs->nsections"));
	sect_attrs = long(gdb.parse_and_eval("(u64)((struct module *)"+str(mod)+")->sect_attrs"));
	for i in range(0, nsections):
		command += " -s";
		tmp = str(gdb.parse_and_eval("((struct module_sect_attrs *)"+str(sect_attrs)+")->attrs["+str(i)+"].name"));
		tmp = tmp[tmp.index("\"")+1:len(tmp)];
		tmp = tmp[0:tmp.index("\"")];
		command += " "+tmp;
		tmp = str(gdb.parse_and_eval("((struct module_sect_attrs *)"+str(sect_attrs)+")->attrs["+str(i)+"].address"));
		command += " "+tmp;

	if mod_dir_name == "":
		print "Can find out",mod_name,"from directory.";
		print "Please use following command load the symbols from it:"
		print "add-symbol-file some_dir/"+mod_name+command;
	else:
		#print "add-symbol-file "+mod_dir_name+command;
		gdb.execute("add-symbol-file "+mod_dir_name+command, False, False);