● Remote debug with gdb hhuu - 荔园在线 | 深圳大学学生论坛,荔园晨风BBS,深大在线网站

荔园之美，在春之萌芽，在夏之绽放，在秋之收获，在冬之沉淀

发信人: jjksam (UNIX+C+XML+??), 信区: Linux
标  题: Remote debug with gdb                  hhuu (转寄)[转载]
发信站: 荔园晨风BBS站 (Wed Apr 17 15:11:05 2002), 转信

【以下文字转载自 jjksam 的信箱】
【原文由 jjksam@smth.org 所发表】
This feature is supported since FreeBSD 2.2, and it's actually a very
neat one.

GDB used to support remote debugging for a long time already. This is
done using a very simple protocol along a serial line. Obviously, and
opposed to the other methods described above, you need two machines
for doing this. One is the host providing the debugging environment,
including all the sources, and a copy of the kernel binary with all
the symbols in it, and the other one is the target machine that simply
runs a similar copy of the very same kernel (but stripped off the
debugging information).

You should configure the kernel in question with config -g, include
DDB into the configuration, and compile it as usual. This gives a
large blurb of a binary, due to the debugging information. Copy this
kernel to the target machine, strip the debugging symbols off with strip
-x, and boot it using the -d boot option. Connect the first serial line
of the target machine to any serial line of the debugging host. Now, on
the debugging machine, go to the compile directory of the target
kernel, and start gdb:

% gdb -k kernel
GDB is free software and you are welcome to distribute copies of it
under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for
details.
GDB 4.16 (i386-unknown-freebsd),
Copyright 1996 Free Software Foundation, Inc...
(kgdb)

Initialize the remote debugging session (assuming the first serial
port is being used) by:

(kgdb) target remote /dev/cuaa0

Now, on the target host (that entered DDB right before even starting the
device probe), type:

Debugger("Boot flags requested debugger")
Stopped at      Debugger+0x35: movb     $0, edata+0x51bc
db> gdb

DDB will respond with:

Next trap will enter GDB remote protocol mode

Every time you type ``gdb'', the mode will be toggled between remote GDB
and local DDB. In order to force a next trap immediately, simply type
``s'' (step). Your hosting GDB will now gain control over the target
kernel:

Remote debugging using /dev/cuaa0
Debugger (msg=0xf01b0383 "Boot flags requested debugger")
    at ../../i386/i386/db_interface.c:257
(kgdb)

You can use this session almost as any other GDB session, including full
access to the source, running it in gud-mode inside an Emacs window
(which gives you an automatic source code display in another Emacs
window) etc.

Remote GDB can also be used to debug LKMs. First build the LKM with
debugging symbols:

# cd /usr/src/lkm/linux
# make clean; make COPTS=-g

Then install this version of the module on the target machine, load it
and use modstat to find out where it was loaded:

# linux
# modstat
Type     Id Off Loadaddr Size Info     Rev Module Name
EXEC      0   4 f5109000 001c f510f010   1 linux_mod

Take the load address of the module and add 0x20 (probably to account
for the a.out header). This is the address that the module code was
relocated to. Use the add-symbol-file command in GDB to tell the
debugger about the module:

(kgdb) add-symbol-file /usr/src/lkm/linux/linux_mod.o 0xf5109020
add symbol table from file "/usr/src/lkm/linux/linux_mod.o" at
text_addr = 0xf5109020?
(y or n) y
(kgdb)

You now have access to all the symbols in the LKM
--
※ 转载:·荔园晨风BBS站 bbs.szu.edu.cn·[FROM: 192.168.0.146]

荔园在线首页友情链接：深圳大学深大招生荔园晨风BBS S-Term软件网络书店