(
来自Linus Torvalds的讨论:
[url][/url]
又，[url][/url]
)
例如这样的一个Oops：
Oops: 0000 [#1] PREEMPT SMP
Modules linked in: capidrv kernelcapi isdn slhc ipv6
loop dm_multipath snd_ens1371 gameport snd_rawmidi snd_ac97_codec
ac97_bus snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq
snd_seq_device snd_pcm_oss snd_mixer_oss snd_pcm snd_timer snd
parport_pc floppy parport pcnet32 soundcore mii pcspkr snd_page_alloc
ac i2c_piix4 i2c_core button power_supply sr_mod sg cdrom ata_piix
libata dm_snapshot dm_zero dm_mirror dm_mod BusLogic sd_mod scsi_mod
ext3 jbd mbcache uhci_hcd ohci_hcd ehci_hcd
Pid: 1726, comm: kstopmachine Not tainted (2.6.24-rc3-module #2)
EIP: 0060:[
] EFLAGS: 00010092 CPU: 0
EIP is at list_del+0xa/0x61
EAX: e0c3cc04 EBX: 00000020 ECX: 0000000e EDX: dec62000
ESI: df6e8f08 EDI: 000006bf EBP: dec62fb4 ESP: dec62fa4
DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
Process kstopmachine (pid: 1726, ti=dec62000 task=df8d2d40 task.ti=dec62000)
Stack: 000006bf dec62fb4 c04276c7 00000020 dec62fbc c044ab4c dec62fd0 c045336c
df6e8f08 c04532b4 00000000 dec62fe0 c043deb0 c043de75 00000000 00000000
c0405cdf df6e8eb4 00000000 00000000 00000000 00000000 00000000
Call Trace:
[] show_trace_log_lvl+0x1a/0x2f
[] show_stack_log_lvl+0x9b/0xa3
[] show_registers+0xa3/0x1df
[] die+0x11f/0x200
[] do_page_fault+0x533/0x61a
[] error_code+0x72/0x78
[] __unlink_module+0xb/0xf
[] do_stop+0xb8/0x108
[] kthread+0x3b/0x63
[] kernel_thread_helper+0x7/0x10
=======================
Code: 6b c0 e8 2e 7e f6 ff e8 d1 16 f2 ff b8 01 00 00
00 e8 aa 1c f4 ff 89 d8 83 c4 10 5b 5d c3 90 90 90 55 89 e5 53 83 ec 0c
8b 48 04 <8b> 11 39 c2 74 18 89 54 24 08 89 44 24 04 c7 04 24 be
32 6b c0
EIP: [] list_del+0xa/0x61 SS:ESP 0068:dec62fa4
note: kstopmachine[1726] exited with preempt_count 1
1, 有自己编译的vmlinux： 使用gdb
编译时打开complie with debug info选项。
注意这行：
EIP is at list_del+0xa/0x61
这告诉我们，list_del函数有0x61这么大，而Oops发生在0xa处。 那么我们先看一下list_del从哪里开始：
# grep list_del /boot/System.map-2.6.24-rc3-module
c10e5234 T plist_del
c10e53cc T list_del
c120feb6 T klist_del
c12d6d34 r __ksymtab_list_del
c12dadfc r __ksymtab_klist_del
c12e1abd r __kstrtab_list_del
c12e9d03 r __kstrtab_klist_del
于是我们知道，发生Oops时的EIP值是：
c10e53cc + 0xa == c10e53d6
然后用gdb查看：
# gdb /home/arc/build/linux-2.6/vmlinux
(gdb) b *0xc10e53d6
Breakpoint 1 at 0xc10e53d6: file /usr/src/linux-2.6.24-rc3/lib/list_debug.c, line 64.
看，gdb直接就告诉你在哪个文件、哪一行了。
gdb中还可以这样：
# gdb Sources/linux-2.6.24/vmlinux
(gdb) l *do_fork+0x1f
0xc102b7ac is in do_fork (kernel/fork.c:1385).
1380
1381 static int fork_traceflag(unsigned clone_flags)
1382 {
1383 if (clone_flags & CLONE_UNTRACED)
1384 return 0;
1385 else if (clone_flags & CLONE_VFORK) {
1386 if (current->ptrace & PT_TRACE_VFORK)
1387 return PTRACE_EVENT_VFORK;
1388 } else if ((clone_flags & CSIGNAL) != SIGCHLD) {
1389 if (current->ptrace & PT_TRACE_CLONE)
(gdb)
也可以直接知道line number。
或者：
(gdb) l *(0xffffffff8023eaf0 + 0xff) /* 出错函数的地址加上偏移 */
2, 没有自己编译的vmlinux： TIPS
如果在lkml或bugzilla上看到一个Oops，而自己不能重现，那就只能反汇编以"Code:"开始的行。 这样可以尝试定位到
源代码中。
注意，Oops中的Code:行，会把导致Oops的第一条指令，也就是EIP的值的第一个字节， 用尖括号<>括起来。 但是，有些
体系结构(例如常见的x86)指令是不等长的(不一样的指令可能有不一样的长度)，所以要不断的尝试(trial-and-error)。
Linus通常使用一个小程序，类似这样：
const char array[] = "\xnn\xnn\xnn...";
int main(int argc, char *argv[])
{
printf("%p\n", array);
*(int *)0 = 0;
}
e.g. /*{{{*/ /* 注意， array一共有从array[0]到array[64]这65个元素， 其中出错的那个操作码<8b> == arry[43] */
#include
#include
const char array[]
="\x6b\xc0\xe8\x2e\x7e\xf6\xff\xe8\xd1\x16\xf2\xff\xb8\x01\x00\x00\x00\xe8\xaa\x1c\xf4\xff\x89\xd8\x83\xc4\x10\x5b\x5d\xc3\x90\x90\x90\x55\x89\xe5\x53\x83\xec\x0c\x8b\x48\x04\x8b\x11\x39\xc2\x74\x18\x89\x54\x24\x08\x89\x44\x24\x04\xc7\x04\x24\xbe\x32\x6b\xc0";
int main(int argc, char *argv[])
{
printf("%p\n", array);
*(int *)0 = 0;
}
/*}}}*/
用gcc -g编译，在gdb里运行它：
[arc@dhcp-cbjs05-218-251 ~]$ gdb hello
GNU gdb Fedora (6.8-1.fc9)
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <[url][/url]>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu"...
(no debugging symbols found)
(gdb) r
Starting program: /home/arc/hello
0x80484e0
Program received signal SIGSEGV, Segmentation fault.
注意，这时候就可以反汇编0x80484e0这个地址：
(gdb) disassemble 0x80484e0
Dump of assembler code for function array:
0x080484e0 : imul $0xffffffe8,%eax,%eax
0x080484e3 : jle,pn 0x80484dc <__dso_handle+20>
0x080484e6 : ljmp *
0x080484e8 : rcll (%esi)
0x080484ea : repnz (bad)
0x080484ec : mov $0x1,%eax
0x080484f1 : call 0x7f8a1a0
0x080484f6 : mov %ebx,%eax
0x080484f8 : add $0x10,%esp
0x080484fb : pop %ebx
0x080484fc : pop %ebp
0x080484fd : ret
0x080484fe : nop
0x080484ff : nop
0x08048500 : nop
0x08048501 : push %ebp
0x08048502 : mov %esp,%ebp
0x08048504 : push %ebx
0x08048505 : sub $0xc,%esp
0x08048508 : mov 0x4(%eax),%ecx
0x0804850b : mov (%ecx),%edx
0x0804850d : cmp %eax,%edx
0x0804850f : je 0x8048529
0x08048511 : mov %edx,0x8(%esp)
0x08048515 : mov %eax,0x4(%esp)
0x08048519 : movl $0xc06b32be,(%esp)
0x08048520 : add %ah,0xa70
End of assembler dump.
(gdb)
OK, 现在你知道出错的那条指令是array[43]，也就是mov (%ecx),%edx，也就是说，(%ecx)指向了一个错误内存地址。
补充：
为了使汇编代码和C代码更好的对应起来， Linux内核的Kbuild子系统提供了这样一个功能： 任何一个C文件都可以单独编译成汇编文件，例如：
make path/to/the/sourcefile.s
例如我想把kernel/sched.c编译成汇编，那么：
make kernel/sched.s V=1
或者：
make kernel/sched.lst V=1
编译出*.s文件
有时侯需要对*.s文件进行分析，以确定BUG所在的位置。 对任何一个内核build目录下的*.c文件，都可以
直接编译出*.s文件。
# make drivers/net/e100.s V=1
而对于自己写的module，就需要在Makefile中有一个灵活的target写法：
# cat Makefile
obj-m := usb-skel.o
KDIR := /lib/modules/`uname -r`/build
traget := modules
default:
make -C $(KDIR) M=$(shell pwd) $(target)
clean:
rm -f *.o *.ko .*.cmd *.symvers *.mod.c
rm -rf .tmp_versions
# make target=usb-skel.s V=1
这样，kbuild系统才知道你要make的目标不是modules，而是usb-skel.s。
另外， 内核源代码目录的./scripts/decodecode文件是用来解码Oops的：
./scripts/decodecode < Oops.txt
(我没用过，就只提一下。)
跟踪module中的oops:
如果是module出现了oops，我们没有编译的内核，不好按照上面的方法跟踪。
Aug 15 15:56:11 localhost kernel: BUG: unable to handle kernel NULL pointer dereference at virtual address 00000004
Aug 15 15:56:11 localhost kernel: printing eip:
Aug 15 15:56:11 localhost kernel: f8922523
Aug 15 15:56:11 localhost kernel: *pde = 00000000
Aug 15 15:56:11 localhost kernel: Oops: 0000 [#1]
Aug 15 15:56:11 localhost kernel: SMP
Aug 15 15:56:11 localhost kernel: last sysfs file: /class/net/eth1/address
Aug 15 15:56:11 localhost kernel: Modules linked in: e1000(U) dum(U) autofs4 hidp rfcomm l2cap bluetooth sunrpc dm_multipath video sbs i2c_ec button battery asus_acpi ac ipv6 parport_pc lp parport intel_rng i2c_i801 tg3 i2c_core serio_raw pcspkr dm_snapshot dm_zero dm_mirror dm_mod ata_piix libata sd_mod scsi_mod ext3 jbd ehci_hcd ohci_hcd uhci_hcd
Aug 15 15:56:11 localhost kernel: CPU: 1
Aug 15 15:56:11 localhost kernel: EIP: 0060:[] Tainted: GF VLI
Aug 15 15:56:11 localhost kernel: EFLAGS: 00010246 (2.6.18-1.2798.fc6 #1)
Aug 15 15:56:11 localhost kernel: EIP is at e1000_unmap_and_free_tx_resource+0x3/0x40 [e1000]
Aug 15 15:56:11 localhost kernel: eax: f4458400 ebx: 00000000 ecx: 00000100 edx: 00000000
Aug 15 15:56:11 localhost kernel: esi: f4458400 edi: 00000001 ebp: f4458000 esp: f7feef20
Aug 15 15:56:11 localhost kernel: ds: 007b es: 007b ss: 0068
Aug 15 15:56:11 localhost kernel: Process events/1 (pid: 9, ti=f7fee000 task=c2f40070 task.ti=f7fee000)
Aug 15 15:56:11 localhost kernel: Stack: f48fb2c0 f8922584 00000034 00000001 f4458400 f8923d45 f4458400 f445849c
Aug 15 15:56:11 localhost kernel: c2f29b40 00000282 f8924e99 00000003 00000092 f44584c8 00000282 00000282
Aug 15 15:56:11 localhost kernel: f4458498 c0433c30 00000000 c2f29b40 c2f29b60 f8924ef0 f4458498 c2f29b60
Aug 15 15:56:11 localhost kernel: Call Trace:
Aug 15 15:56:11 localhost kernel: [] e1000_clean_tx_ring+0x24/0xa0 [e1000]
Aug 15 15:56:11 localhost kernel: [] e1000_down+0x125/0x1b0 [e1000]
Aug 15 15:56:11 localhost kernel: [] e1000_reinit_locked+0x39/0x90 [e1000]
Aug 15 15:56:11 localhost kernel: [] run_workqueue+0x83/0xc5
Aug 15 15:56:11 localhost kernel: [] worker_thread+0xd9/0x10d
Aug 15 15:56:11 localhost kernel: [] kthread+0xc0/0xed
Aug 15 15:56:11 localhost kernel: [] kernel_thread_helper+0x7/0x10
使用gdb加载e1000.ko:
root@dell-desktop:/home/dell/libppf/e1000-7.6.5/src# gdb ./e1000.ko
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...
(gdb) b *e1000_unmap_and_free_tx_resource+0x3b
Breakpoint 1 at 0x260b: file /home/dell/libppf/e1000-7.6.5/src/e1000_main.c, line 2637.
(gdb) l /home/dell/libppf/e1000-7.6.5/src/e1000_main.c:2637
2632 */
2633 #if 0
2634 dev_kfree_skb_any(buffer_info->skb);
2635 #else
2636 if (XXX) {
2637 YYY ();
2640 } else
2641 dev_kfree_skb_any(buffer_info->skb);
我们就找到了出问题的行号了 :-)
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