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Kernel Oops

当我们编写的Linux内核程序含有Bug时会出现下面所示的情况，屏幕输出内核错误信息，我们称之为Oops。此时系统需要重启才能继续使用。

注意，这里有三行十分重要。BUG指出了错误原因，IP寄存器的值则指出了错误位置相对于函数开始位置的偏移量。比如下面的出错位置在距离函数hydra_hook_func_out开始位置偏移量为0xb8的机器代码处。后文还会提到它们。Oops指出了错误代码，含义如下：

  • bit 0 == 0 means no page found, 1 means protection fault
  • bit 1 == 0 means read, 1 means write
  • bit 2 == 0 means kernel, 1 means user-mode
  • bit 3 == 0 means data, 1 means instruction

这里的错误代码 0000 意思是内核数据读错误。 #1 表示这个错误发生一次。

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[  804.963442] BUG: unable to handle kernel NULL pointer dereference at           (null)
[  804.964875] IP: [<ffffffffc07a10b8>] hydra_hook_func_out+0xb8/0x140 [hydra]
[  804.966112] PGD 7af27067 PUD 7bead067 PMD 0 
[  804.966924] Oops: 0000 [#1] SMP 
[  804.967556] Modules linked in: hydra(O) tyz_memfs(O) rfcomm bnep bluetooth snd_ens1371 snd_ac97_codec ac97_bus gameport snd_pcm vmwgfx snd_seq_midi snd_seq_midi_event snd_rawmidi coretemp snd_seq crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel snd_seq_device snd_timer aes_x86_64 ttm lrw snd gf128mul glue_helper ablk_helper cryptd vmw_balloon drm_kms_helper soundcore serio_raw drm 8250_fintek i2c_piix4 shpchp vmw_vmci parport_pc mac_hid ppdev lp parport hid_generic usbhid hid mptspi mptscsih psmouse mptbase e1000 ahci libahci scsi_transport_spi pata_acpi floppy vmw_pvscsi vmxnet3
[  804.978080] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G           O   3.19.0 #1
[  804.979272] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
[  804.981242] task: ffffffff81c1c4e0 ti: ffffffff81c00000 task.ti: ffffffff81c00000
[  804.982511] RIP: 0010:[<ffffffffc07a10b8>]  [<ffffffffc07a10b8>] hydra_hook_func_out+0xb8/0x140 [hydra]
[  804.984235] RSP: 0018:ffff88007f603698  EFLAGS: 00010096
[  804.985195] RAX: 000000000000000c RBX: ffff8800641ccf00 RCX: 0000000000003162
[  804.986422] RDX: 000000000000000a RSI: ffff88007f6036a0 RDI: 0000000000000000
[  804.987635] RBP: ffff88007f6036d8 R08: 0000000000000092 R09: 296c6c756e28203a
[  804.988851] R10: 0000000000000688 R11: ffff88007f6033ee R12: ffffffff816d57f0
[  804.990152] R13: ffff88002dca4000 R14: 00000000000009f8 R15: 0000000000000282
[  804.991415] FS:  0000000000000000(0000) GS:ffff88007f600000(0000) knlGS:0000000000000000
[  804.992798] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  804.993818] CR2: 0000000000000000 CR3: 000000007a402000 CR4: 00000000001407f0
[  804.995087] Stack:
[  804.995447]  ffff88007f613e00 ffff88007f603700 ffffffff810ac912 ffff88007f603780
[  804.997277]  ffffffff816d57f0 ffff88002dca4000 0000000000000000 ffff8800641ccf00
[  804.998657]  ffff88007f603738 ffffffff816ca71a ffff88007f603787 ffffffff81d1f460
[  805.000038] Call Trace:
[  805.000466]  <IRQ> 
[  805.000821]  [<ffffffff810ac912>] ? enqueue_task_fair+0x422/0x6a0
[  805.001986]  [<ffffffff816d57f0>] ? ip_fragment+0x8a0/0x8a0
[  805.002951]  [<ffffffff816ca71a>] nf_iterate+0x9a/0xb0
[  805.003836]  [<ffffffff816d57f0>] ? ip_fragment+0x8a0/0x8a0
[  805.004836]  [<ffffffff816ca7a4>] nf_hook_slow+0x74/0x130
[  805.005768]  [<ffffffff816d57f0>] ? ip_fragment+0x8a0/0x8a0
[  805.006723]  [<ffffffff816d74c2>] ip_output+0x92/0xa0
[  805.007593]  [<ffffffff8101d2c9>] ? sched_clock+0x9/0x10
[  805.008509]  [<ffffffff816d6bd0>] ip_local_out_sk+0x30/0x40
[  805.009480]  [<ffffffff816d6d43>] ip_build_and_send_pkt+0x163/0x220
[  805.010547]  [<ffffffff816f67d5>] tcp_v4_send_synack+0x65/0xc0
[  805.011538]  [<ffffffff816f7d5d>] ? tcp_openreq_init_rwin+0xbd/0x1c0
[  805.012624]  [<ffffffff816e44c5>] tcp_conn_request+0x4f5/0x750
[  805.013620]  [<ffffffff8101c493>] ? nommu_map_page+0x43/0x80
[  805.014586]  [<ffffffff816f42fd>] tcp_v4_conn_request+0x4d/0x50
[  805.015652]  [<ffffffff81765765>] tcp_v6_conn_request+0x65/0x70
[  805.017675]  [<ffffffff816ebc10>] tcp_rcv_state_process+0x1a0/0xf30
[  805.018771]  [<ffffffff816daf26>] ? __inet_lookup_established+0x46/0x130
[  805.019921]  [<ffffffff816f59da>] tcp_v4_do_rcv+0x15a/0x380
[  805.020903]  [<ffffffff81305036>] ? security_sock_rcv_skb+0x16/0x20
[  805.021977]  [<ffffffff816acb50>] ? sk_filter+0x30/0xe0
[  805.022862]  [<ffffffff816f7158>] tcp_v4_rcv+0x7c8/0x980
[  805.023780]  [<ffffffff816cf8de>] ? ip_route_input_noref+0xaee/0xc10
[  805.024864]  [<ffffffff816d132c>] ip_local_deliver_finish+0xac/0x220
[  805.025957]  [<ffffffff816d1638>] ip_local_deliver+0x48/0x80
[  805.027618]  [<ffffffff816d0fa1>] ip_rcv_finish+0x81/0x360
[  805.028640]  [<ffffffff816d1912>] ip_rcv+0x2a2/0x3f0
[  805.029606]  [<ffffffff81697e92>] __netif_receive_skb_core+0x552/0x790
[  805.030728]  [<ffffffff8104d525>] ? ack_ioapic_level+0x75/0x130
[  805.031782]  [<ffffffff816980e8>] __netif_receive_skb+0x18/0x60
[  805.032790]  [<ffffffff81698153>] netif_receive_skb_internal+0x23/0x90
[  805.033906]  [<ffffffff81698d98>] napi_gro_receive+0xc8/0x100
[  805.034927]  [<ffffffffc04644dd>] e1000_clean_rx_irq+0x2bd/0x4f0 [e1000]
[  805.036159]  [<ffffffffc0464edb>] e1000_clean+0x25b/0x8c0 [e1000]
[  805.037208]  [<ffffffff816985a9>] net_rx_action+0x159/0x340
[  805.038163]  [<ffffffff81078bf4>] __do_softirq+0xe4/0x270
[  805.039101]  [<ffffffff81078fbd>] irq_exit+0x9d/0xb0
[  805.039948]  [<ffffffff817a664a>] do_IRQ+0x5a/0xf0
[  805.040789]  [<ffffffff817a44ad>] common_interrupt+0x6d/0x6d
[  805.041785]  <EOI> 
[  805.042139]  [<ffffffff8105a8f6>] ? native_safe_halt+0x6/0x10
[  805.043206]  [<ffffffff8101e2de>] default_idle+0x1e/0xc0
[  805.044123]  [<ffffffff8101ec5f>] arch_cpu_idle+0xf/0x20
[  805.045037]  [<ffffffff810b4a00>] cpu_startup_entry+0x370/0x3a0
[  805.046294]  [<ffffffff8178c937>] rest_init+0x77/0x80
[  805.047331]  [<ffffffff81d3a0fc>] start_kernel+0x494/0x4a1
[  805.048313]  [<ffffffff81d39a58>] ? set_init_arg+0x55/0x55
[  805.049251]  [<ffffffff81d39120>] ? early_idt_handlers+0x120/0x120
[  805.050308]  [<ffffffff81d395ee>] x86_64_start_reservations+0x2a/0x2c
[  805.051441]  [<ffffffff81d39733>] x86_64_start_kernel+0x143/0x152
[  805.052483] Code: 35 f6 32 f7 ff 49 89 c7 48 c7 c7 95 20 7a c0 31 c0 66 41 c1 c6 08 e8 cb 5c ff c0 48 8b 3d d9 32 f7 ff 48 8d 75 c8 ba 0a 00 00 00 <44> 0f be 2f 48 83 c7 02 e8 7b c7 bf c0 4c 89 fe 49 89 c4 48 c7 
[  805.057417] RIP  [<ffffffffc07a10b8>] hydra_hook_func_out+0xb8/0x140 [hydra]
[  805.058638]  RSP <ffff88007f603698>
[  805.059248] CR2: 0000000000000000
[  805.059822] ---[ end trace d6119da9259d40ec ]---
[  805.060965] Kernel panic - not syncing: Fatal exception in interrupt
[  805.062262] Kernel Offset: 0x0 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[  805.063971] ---[ end Kernel panic - not syncing: Fatal exception in interrupt

获取调试信息

使用printk函数和dmesg命令

这是最基本的用法，把怀疑出错的地方打印出来再检验。假如没有内核没有出错或者已经注释掉可能出错的部分，可以用此法。

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系统环境

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$ cat /etc/issue
Ubuntu 16.04.2 LTS \n \l
$ uname -a
Linux satsuma-pc 4.4.0-62-generic #83-Ubuntu SMP 
Wed Jan 18 14:10:15 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

安装eclipse

有多种方式安装eclipse：

  1. sudo apt-get install eclipse
  2. 利用ubuntu-make安装
  3. 去官网下载安装最新版本。

这里第一种方法安装的eclipse是老版本，3.8.1，不推荐。

第二种方法里ubuntu-make是为开发人员提供快速安装各种开发环境的命令行工具。在github上有维护,地址在这里。安装步骤可以参考github指南。这里需要注意的是最好添加ppa源，以获取最新版本，否则后续安装IDE可能会出错。

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$ sudo add-apt-repository ppa:ubuntu-desktop/ubuntu-make

第三种官网下载，解压后运行即可安装

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./eclipse-inst

本文最终使用第三种方法，这里安装的版本是Neon.2 Release (4.6.2)。

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